BS 8701:2016
BSI Standards Publication
Full ring ovalization test for
determining the
susceptibility to cracking of
linepipe steels in sour
service – Test method
BS 8701:2016
BRITISH STANDARD
Publishing and copyright information
The BSI copyright notice displayed in this document indicates when the document
was last issued.
© The British Standards Institution 2016
Published by BSI Standards Limited 2016
ISBN 978 0 580 89474 9
ICS 77.060
The following BSI references relate to the work on this document:
Committee reference PSE/17
Draft for comment 16/30319903 DC
Publication history
First published June 2016
Amendments issued since publication
Date
Text affected
BRITISH STANDARD
BS 8701:2016
Contents
Foreword
iii
Introduction
1
2
3
4
5
6
7
8
9
10
1
Scope 1
Normative references 2
Terms and definitions 2
Principle 5
Reagents 5
Apparatus 6
Samples 6
Surface preparation 7
Procedure for test specimens with internal loading
Expression of results 12
7
Annexes
Annex A (normative) Ultrasonic examination of pipe, plate and welds during
accelerated laboratory tests 13
Annex B (normative) Ring loading 17
Annex C (informative) Typical internal and external load application rigs for use
in the full ring test 27
Annex D (normative) Chemistry of test solutions 28
Annex E (informative) Analysis of test solution – iodimetric titration
procedure 29
Annex F (informative) Illustrated summary of the full ring test procedure 30
Annex G (informative) Hydrogen sulfide (H2S) health and safety
considerations 38
Annex H (informative) Sample identification and test record, Form 1 39
Annex I (informative) Sample identification and test record, Form 2 40
Annex J (informative) Acceptance criteria 43
Annex K (informative) Sulfide stress corrosion (SSC) and hydrogen induced
cracking (HIC) 43
Annex L (informative) Explanatory notes on test method: Galvanic Coupling 45
Annex M (informative) Modified test procedure for externally loaded test
specimens (Diameter <12 in. [305 mm]) 45
Annex N (informative) Magnetic particular inspection (MPI) procedure 46
Bibliography
47
List of figures
Figure 1 – Full ring test using internal loading techniques 8
Figure 2 – Modified full ring test using external loading technique 8
Figure A.1 – Most common crack locations 13
Figure B.1 – Gauge positions for seamless ring specimens 20
Figure B.2 – Gauge positions for ring specimens that contain only a longitudinal
seam weld 21
Figure B.3 – Gauge positions on specimens having a spirally wound seam
only 22
Figure B.4 – Gauge positions for ring specimens that contain only a girth weld
seam 22
Figure B.5 – Gauge positions for ring specimens that contain both
circumferential and longitudinal weld seams and have an angular gap of
between 5° and 175° between longitudinal seams 23
Figure B.6 – Modified gauge positions for ring specimens that contain both
circumferential and longitudinal weld seams and have an angular off-set
of <5° or 175° to 185° between longitudinal weld seams 24
Figure B.7 – Gauge positions on specimens having spirally wound weld seams
combined with a girth weld 24
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Figure B.8 – Gauge positions for ring specimens that contain both
circumferential and longitudinal weld seams where individual plates are of
unequal thickness 25
Figure C.1 – External loading blocks used for ring specimens below 12 in.
(305 mm) in diameter 27
Figure C.2 – Internal loading rig used for ring specimens above 12 in. (305 mm)
in diameter 28
Figure F.1 – Ring machined and grit blasted 31
Figure F.2 – Ring strain gauged 32
Figure F.3 – Application of internal and external loads 32
Figure F.4 – Conversion of ring into test cell 33
Figure F.5 – On-line ultrasonic inspection 34
Figure F.6 – Full ring after test 34
Figure F.7 – Example of ultrasonic indications after test 35
Figure F.8 – Example of recorded permeation data 35
Figure F.9 – Typical HIC crack 36
Figure F.10 – Typical weld SSC 37
Figure F.11 – Typical soft zone crack 37
Figure F.12 – Typical SOHIC 38
Figure H.1 – Sample identification and test record, Form 1 39
Figure I.1 – Full ring test loading data sheets, Form 2 40
Figure L.1 – Typical example of potential change on a girth welded sample 45
List of tables
Table B.1 – Load level ranges 26
Table D.1 – Standard NACE TM0177 solution A composition 29
Table D.2 – Highly buffered solution composition 29
Table F.1 – List of full ring test procedure figures 31
Table G.1 – Chemical and physical properties of hydrogen sulfide
38
Summary of pages
This document comprises a front cover, an inside front cover, pages i to iv,
pages 1 to 48, an inside back cover and a back cover.
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BS 8701:2016
Foreword
Publishing information
This British Standard is published by BSI Standards Limited, under licence from
The British Standards Institution, and came into effect on 30 June 2016. It was
prepared by Technical Committee PSE/17, Materials and equipment for
petroleum, petrochemical and natural gas industries. A list of organizations
represented on this committee can be obtained on request to its secretary.
Use of this document
It has been assumed in the preparation of this British Standard that the
execution of its provisions will be entrusted to appropriately qualified and
experienced people, for whose use it has been produced.
Presentational conventions
The provisions of this standard are presented in roman (i.e. upright) type. Its
methods are expressed as a set of instructions, a description, or in sentences in
which the principal auxiliary verb is “shall”.
Commentary, explanation and general informative material is presented in
smaller italic type, and does not constitute a normative element.
Where words have alternative spellings, the preferred spelling of the Shorter
Oxford English Dictionary is used (e.g. “organization” rather than
“organisation”).
Contractual and legal considerations
This publication does not purport to include all the necessary provisions of a
contract. Users are responsible for its correct application.
Compliance with a British Standard cannot confer immunity from legal
obligations.
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BS 8701:2016
Introduction
Sour service cracking problems in susceptible pipeline steels are caused by the
various forms of hydrogen damage due to the presence of wet hydrogen sulfide
(H2S). The main mechanisms are hydrogen pressure induced cracking (HPIC) [also
called hydrogen induced cracking (HIC) or stepwise cracking (SWC)], sulfide stress
corrosion (SSC) and stress oriented hydrogen induced cracking (SOHIC). An
industry proven technique for assessing pipeline steels is to stress a full ring
specimen in a sour environment.
The advantage of the full ring test specified in this British Standard is that it is
not necessary to pressurize the linepipe full ring specimen to achieve the
required stress loading and residual stresses are retained. Equivalent stresses can
be produced using mechanical means to deform the pipe by ovalization.
Additional advantages are representative sample and single sided exposure.
This test uses well tried experimental procedures to exert a known stress level at
two regions on a full ring section of pipe steel. The pipe specimen is then
exposed internally to the sour test solution, although some cases require the
sour media externally. Ultrasonic monitoring and hydrogen permeation
measurements are conducted regularly during the exposure period. Both crack
initiation and propagation can therefore be monitored. Finally, a metallographic
study of indications is undertaken to classify any defects found by the ultrasonic
survey.
The method has been in use since 1984, but in 1991 a Joint Industry Sponsored
Project was set up with the aim of systematically developing, defining and
validating the full ring test. The resultant test method designed to determine
the susceptibility of pipeline steels, bends, flanges and fittings, including all
associated welds to hydrogen damage caused by exposure to sour environments,
was published by the UK HSE as OTI 95 635 [1] and forms the basis of this British
Standard.
1 Scope
This British Standard gives a method for determining the susceptibility to
cracking of steel pipes in sour service.
This British Standard utilizes a tubular specimen comprising a full circumferential
ring. The test method applies to any pipe with or without seam (longitudinal or
spiral) or girth weld (with or without filler).
NOTE 1 The specimen is usually a pipe but can also consist of flange neck or section
of a bend, or other tubular component or a combination of the above.
This British Standard provides guidance on determination of specimen size to
ensure it retains residual stresses from manufacture and welding.
NOTE 2
See Clause 7 for specimen sizes.
The method utilizes ovalization to simulate hoop stress, using mechanical
loading on a tubular form. The specimen is subjected to single sided exposure to
the sour test environment.
NOTE 3 The test also allows measurement of hydrogen permeation rates which can
provide useful information, such as highlighting the effects of galvanic coupling
between materials of apparent compatibility.
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2 Normative references
The following documents, in whole or in part, are normatively referenced in this
document and are indispensable for its application. For dated references, only
the edition cited applies. For undated references, the latest edition of the
referenced document (including any amendments) applies.
BS EN 12668 (all parts), Non-destructive testing – Characterization and
verification of ultrasonic examination equipment
BS EN ISO 2400, Non-destructive testing – Ultrasonic testing – Specification for
calibration block No.1
BS EN ISO 7963, Non-destructive testing – Ultrasonic testing – Specification for
calibration block No.2
BS EN ISO 8044, Corrosion of metals and alloys – Basic terms and definitions
BS EN ISO 9712, Non-destructive testing – Qualification and certification of NDT
personnel
BS EN ISO 11666, Non-destructive testing of welds – Ultrasonic testing –
Acceptance levels
BS EN ISO 16810, Non-destructive testing – Ultrasonic testing – General principles
BS EN ISO 17640, Non-destructive testing of welds – Ultrasonic testing –
Techniques, testing levels, and assessment
ASTM D1193, Standard Specification for Reagent Water
Other publications
[N1]NACE TM0177, Laboratory Testing of Metals for Resistance to Sulfide Stress
Cracking in H2S Environments. NACE International, PO Box 218340, Houston,
TX. 77218.
3 Terms and definitions
For the purposes of this British Standard, the terms and definitions given in
BS EN ISO 8044 and the following apply.
3.1
ancillary components
parts of the apparatus necessary for the test which are not the loading
components to impart stress
3.2
anodic
reaction involving an oxidation process and conjoint generation of electrons
3.3
cathodic
reaction involving a reduction process with conjoint consumption of electrons
3.4
free corrosion potential
naturally occurring electrode potential measured against a standard reference
adopted by a metal undergoing corrosion in an aqueous environment
3.5
galvanic coupling
electrical contact between two or more materials which exhibit different free
corrosion potentials within the same electrolyte, resulting in a combined mixed
potential and an increased oxidation rate on the anodic material driven by the
more noble material, determined by the relative areas and governed by
efficiency of the cathodic reduction
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girth weld
butt weld joining one pipe to another (or bend or flange)
3.7
hardness
resistance of metal to plastic deformation, usually determined by indentation
3.8
heat affected zone (HAZ)
portion of base metal not melted during brazing, cutting or welding, but whose
microstructure and properties are altered by the thermal cycle of these processes
3.9
hydrogen embrittlement
action of absorbed atomic hydrogen to cause loss of ductility in a metal
NOTE Hydrogen atoms are attracted to grain boundaries and slip plane movement
is reduced.
3.10
hydrogen flux
rate of hydrogen flow per unit area through a material
3.11
hydrogen pressure induced cracking (HPIC)
cracking caused by atoms of hydrogen concentrating at discontinuities and
forming molecular hydrogen within the steel
NOTE 1
The resultant gas pressure induces cracking.
NOTE 2 This is also called hydrogen induced cracking (HIC), stepwise cracking and
blister cracking (HIBC).
3.12
hydrogen permeation
process of atomic hydrogen diffusion through a metal
3.13
longitudinal weld
straight weld running along the longitudinal axis of a pipe
3.14
low alloy steel
steel with a total alloying element content of less than approximately 5% but
more than specified for carbon steel
3.15
measured strain
E1, E2, E3
surface strain as measured by various techniques in one or more of three known
directions at the surface
3.16
microstructure
crystalline structure of a metal as revealed by the microscopic examination of a
suitably prepared specimen
3.17
stress
applied force per unit area existing on any object as a result of external
mechanical or thermal influences acting in that direction
3.18
partial pressure
total pressure multiplied by its mole fraction equal to each component in a gas
mixture
NOTE For an ideal gas, the mole fraction is equal to the volume fraction of the
component.
3.19
plastic deformation
permanent deformation caused by straining beyond the elastic limit
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3.20
Poisson effect
component subjected to loading in one direction causing extension or
compression in that direction, experiencing tangentially a lesser opposing
compression or expansion
3.21
Poisson’s ratio
v
dimensionless material constant (approximately constant for steel) given by the
ratio of contraction/expansion per unit length tangential to the direction of
loading over the expansion/contraction per unit length in the direction of
loading
3.22
principal strain
Ex,y
maximum and minimum strain levels existing at a point on the test surface
acting at 90° to each other as calculated from measured strain values
3.23
residual stress
δres
stress present in a component free of external forces or thermal gradients
3.24
stress oriented hydrogen induced cracking (SOHIC)
staggered small cracks formed approximately perpendicular to the principal
stress (residual or applied) resulting in a “ladder-like” crack array linking
(sometimes small) pre-existing HIC cracks
3.25
sour environment
environment where hydrogen sulfide exists in the presence of water
NOTE
3.26
For steel products a threshold concentration is usually applied.
spiral weld
weld running spirally (helically) around the circumference of a pipe formed from
strip
3.27
strain
E
dimensionless ratio of the change in length per unit length (e.g. mm/mm) and is
normally expressed in parts per million (E × 106) of microstrain (µƐ)
3.28
specified minimum yield strength (SMYS)
relates to the minimum yield strength permitted for a given grade of material in
product specifications
3.29
strain gauge
device using electrical resistance, which changes in proportion to applied strain
3.30
sulfide stress cracking
brittle failure by cracking under the combined action of tensile stress and
corrosion in the presence of water and hydrogen sulfide
3.31
tensile strength
in tensile testing the ratio of maximum load to original cross-sectional area
3.32
tensile stress
net tensile component of all combined stresses
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NOTE These stresses include axial or longitudinal, circumferential or hoop and
residual.
3.33
ultrasonic inspection
inspection of material by ultrasound for the presence of flaws
3.34
welding
joining of two metallic materials, usually by fusion techniques
3.35
yield strength
stress at which a material exhibits a specified deviation from the proportionality
of stress to strain
NOTE The deviation is expressed in terms of strain either by the offset method
(usually at a strain of 0.2%) or the total-extension-under- load method (usually at a
strain of 0.5%) (see ASTM A370).
3.36
Young’s modulus of elasticity
relationship between stress and strain within the limits of elastic behaviour
expressed as
E5
δ
ε
where:
δ
is stress;
ε
is strain.
4 Principle
A full ring section of material of a tubular form shall be mechanically loaded to
a predetermined strain by ovalization and exposed to an agreed sour
environment. Testing shall be undertaken within an enclosure or in a restricted
area.
The specimen shall be monitored throughout the test exposure to determine the
extent of development of environmentally assisted cracking, and then subjected
to post-test destructive examination.
5 Reagents
5.1 A solution made using water type IV in accordance with ASTM D1193, or
purer shall be used.
5.2 Inert gas shall be used for removal of oxygen. Inert gas shall mean high
purity (99.5% or higher) nitrogen, argon, or other suitable nonreactive gas.
5.3 Reagents with high purity of 99.5% or higher shall be used.
5.4
Test solutions and gases
The composition and preparation of solutions shall be carried out in accordance
with Annex D.
NOTE
Three test solutions may be used with this method:
a)
NACE TM0177 [N1] Solution A; The initial pH is between 2.7 and 2.9 rising to
approximately 4 by the end of the 30 day test period;
b)
NACE TM0177 [N1] Solution A buffered to maintain pH 3.2 by addition of acetic
acid/sodium acetate;
c)
field specific test solution.
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6 Apparatus
6.1
6.1.1
Containment materials
Lid and base
Lid and base shall be made of either:
a)
polymethylmethacrylate (also known as acrylic) of appropriate thickness to
avoid deformation with surfaces pre-treated with 50% acetic acid solution,
or;
b)
other material that has been proven not to affect the test solution or be
degraded by the test environment.
The materials and thickness used shall be demonstrated to restrict permeation of
H2S to the atmosphere and O2 contamination of the test environment.
NOTE This should be assessed using a lid and base of the same surface area to
volume ratio as used in the test.
6.1.2
Seal rings
Seal rings shall be made of natural rubber or other material that has been
proven not to affect the test solution, be degraded by the test environment, or
allow permeation of H2S to the atmosphere or O2 contamination of the test
environment.
6.2
Internal loading components
6.2.1
Turnbuckle for internal loading
The turnbuckle shall consist of a barrel with a left and right handed thread bore
into which two sections screw with the appropriate thread.
NOTE 1
Ballistic threading is recommended.
NOTE 2 Austenitic stainless steel has been found to be reusable and has not led to
detrimental galvanic effects.
6.2.2
Load blocks
Load blocks shall consist of a galvanically compatible material to that of the
internal surface of the specimen. The load distribution blocks shall be sufficiently
rigid to ensure that the load is evenly distributed without the blocks bending.
6.3
External loading components
External loading blocks shall be sufficiently rigid to ensure that the load is
evenly distributed without the blocks bending.
6.4
Ancillary components
Ancillary components in contact with or exposed to the test environment, such
as thermowells, shall be compatible with the test solution and not degrade or
affect the solution.
NOTE This may be assessed by visually examining the component or more simply by
selecting corrosion resistant alloys suitable for H2S exposure (see BS EN ISO 15156-3).
7 Samples
The sample(s) shall be typical of the as delivered product and any weld shall be
made using an appropriate welding procedure per client requirements.
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NOTE 1 Additional material is required to provide the tensile specimens for data to
support test configuration.
Test samples that contain a full girth weld shall have the weld positioned at the
mid-length of the test piece. To retain the residual stress produced during
manufacture and welding, the length of the test pipe shall be equal to, or
greater than, the diameter.
If the test piece is to contain a specific region for assessment (e.g. a repair weld
or strained area) then this position shall be clearly marked on the external
surface so that the applied load can be aligned accordingly.
NOTE 2 9.2.2 provides guidance on the alignment of seam welds, repair welds, etc.
to optimize the data generated per test specimen.
The ends of the test piece shall be machined to provide clean, flat surfaces so
that these can be later sealed to form a gas tight fit.
8 Surface preparation
8.1
Surface preparation for carbon steel
Unless otherwise directed by the client, the internal surface preparation by grit
blasting to Sa 21⁄2 using Garnet (20-40 mesh) shall be undertaken using new grit.
The grit shall not be recycled.
NOTE Other surface finishes including as-received may be used by agreement with
the client.
To avoid flash rusting of the cleaned surface, after completion of grit blasting or
other surface preparation, the ring specimen shall be loaded and sealed as soon
as possible or stored in a dry atmosphere.
8.2
Surface preparation for corrosion-resistant alloys
Unless otherwise directed by the client, the internal surface shall be degreased
but otherwise not abraded.
9 Procedure for test specimens with internal
loading
9.1
Ultrasonic inspection
Prior to the section being prepared for test, the external surface shall be 100%
inspected using the ultrasonic test procedure detailed in Annex A. The section
shall be inspected using a compression probe and shear probes of
angles 45°, 60° and 70°. All indications shall be recorded. This technique is very
sensitive and the evidence of pre-test indications shall not be taken as indicative
of problems.
NOTE The purpose of this inspection is to provide a “fingerprint” which will enable
a quantitative comparison to be made with later inspections and to avoid failing a
specimen by considering pre-existing indications to have been produced during the
test.
The couplant used for the ultrasonic inspection shall be silicone-free because
silicone compounds/greases are very detrimental to strain gauge adhesion and
can cause errors in load monitoring (see A.3.2.7).
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9.2
9.2.1
Sample loading
Strain gauge locations
The ring sample shall be loaded by mechanical jacking as illustrated in
Figure 1 and Figure 2. To monitor the load and determine the stress during
application of the load, strain gauges shall be attached to the internal surface,
(see Annex B). The position of these gauges shall be determined according
to 9.2.2 and 9.2.3.
Figure 1
Full ring test using internal loading techniques
Key
1
Load distribution blocks
2
Strain gauges
Figure 2
•
Turnbuckle
Location of maximum tensile stress
Modified full ring test using external loading technique
Key
1
Bolts
2
Threaded block
3
Clearance hole
8
3
4
4
5
6
Strain gauges
Location of maximum tensile strength
Pipe sample
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Load distribution block
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9.2.2
BS 8701:2016
Position of maximum load
Prior to application of strain gauges and actually loading the sample, the two
positions of maximum applied stress shall be selected. The following two criteria
shall be used:
a)
the area adjacent to the seam weld (if present) shall be at maximum stress;
or
b)
any ultrasonic indications found in the girth weld or weld repair shall be at
the position of maximum stress.
NOTE 1 It is therefore useful to consider these points prior to producing the test
piece as it is possible for the repair area in a girth weld to be positioned 180° from a
seam weld, in which case both critical areas can be tested simultaneously.
NOTE 2 It is common industrial practice when lengths of seam welded pipe are
welded together, that the two pipe seam welds are a minimum of 30° apart. For
efficient testing, placing the seam welds 180° apart is useful as both seams can then
be positioned at the location of maximum stress. This is warranted if the two
sections are in some way different. If the sections are identical, a standard
approximately 30° spacing should be made.
NOTE 3 Annex B provides details of the strain gauging technique and also shows
the various combinations of ring samples which can be tested.
9.2.3
Strain gauging
The procedure for strain gauging shall be carried out in accordance with
Annex B.
NOTE 1 The procedure covers eight categories of ring sample, from seamless pipe,
spirally welded pipe to a girth welded sample of unequal wall thickness. In summary,
strain gauges are attached at the positions of maximum stress, with other strain
gauges positioned to monitor the stress distribution. It is essential that the
requirements in Annex B are followed in order that inaccurate loading does not
occur. In addition to single element gauges, several “T” gauges or biaxal gauges are
used in order that compensation for the Poisson effect can be made.
NOTE 2 Annex B also contains an example format for reporting the strain gauging
and loading data.
9.2.4
Loading levels
The loading to be adopted in testing shall be agreed with the user in advance.
NOTE Loading for the test specimen has typically reflected the stress induced under
the design conditions, which is predicated upon the SMYS of the line pipe steel.
During the latter part of the 20th Century, 72% SMYS was a common loading
requirement, although with changes in pipeline design basis, 80% SMYS has become
an increasingly common requirement in the 21st Century.
9.2.5
Loading technique
The loading shall be undertaken using a turnbuckle or external bolting
arrangement and two load distribution blocks as shown in Figure 1 and
Figure 2 respectively.
The face of the distribution block which fits against the ring section shall be
profiled preferably to fit the ring section.
NOTE 1 A range of blocks is required if a number of different diameter pipes are to
be tested.
Loading shall commence once the two loading blocks and turnbuckle/bolting are
in position and the strain gauges are zeroed.
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NOTE 2 For thin walled ring sections, the load can be applied manually by turning
the centre section of the turnbuckle. For thicker sections, a hydraulic jack positioned
under but as near to the turnbuckle as possible should be used. In the latter case, as
the load is applied, the turnbuckle is tightened and locked when the required stress
level is reached. The hydraulic jack is then released. It should be noted that when
using a hydraulic jack, the stress level will drop slightly when the jack is released, a
higher stress level might have to be attained before release so that the final relaxed
stress level is as required. Care should be taken to avoid excessive load increases and
small increments should be applied, e.g. 5%.
Once the load has been applied, data collected from all the strain gauges shall
be recorded and converted into a stress value, usually expressed as% SMYS. The
ring sample shall be left for a minimum of 30 min and monitored to ensure no
relaxation or settling takes place. If this does occur, then the load shall be
corrected. When the final level is achieved, the strain gauges shall be removed,
taking care not to damage or score the surface, and the gauge areas cleaned
and degreased. Any other contaminated areas shall also be cleaned and
degreased.
9.3
Cell containment
The loaded ring sample shall be converted into the test cell by fitting gas tight
lids/seals to each end. There are various methods to achieve this and any
method meeting the following criteria shall be used:
•
the materials used for the lids and seals shall not contaminate the test
solution and extensive use of vulcanized rubber should be avoided
(see 6.1.1);
•
the lids and fittings shall not be so rigid as to contribute to the pipe rigidity,
for instance, a welded steel plate shall not be used;
•
the material shall be strong enough to withstand the small gas pressure
above the liquid environment.
NOTE 1 The lid and base can be attached by drilling and tapping the ring sample
and bolting the lids to the pipe.
NOTE 2 The lid can be easily drilled to provide sampling and access points, etc. In
addition, the lid, being transparent, allows visual checking of solution levels, etc.
In addition the materials and seals shall ensure the test environment remains
isolated from all personnel.
NOTE 3 H2S is an extremely toxic gas and should be handled with care,
see Annex G..
After the test section has been made into the test cell it shall be moved into the
safety enclosure or restricted area where the exposure test shall be undertaken.
The test cell shall then be purged in accordance with 5.2 to protect the clean
inner surface and to remove oxygen to a concentration of less than or equal
to 50ppb (carbon and low alloy steels) or 10 ppb for corrosion resistant alloys
prior to filing with the test solution.
9.4
Hydrogen permeation monitoring
If hydrogen cells are to be fitted they shall be attached after loading and cell
containment. For single material ring tests a single cell attachment shall be
sufficient. For girth welded full rings of differing materials, two cells shall be
required. All cells shall be fitted in areas of low applied stress as the presence of
such cells inhibits ultrasonic inspection of these areas, required during test.
NOTE It is desirable, although not mandatory, that hydrogen permeation
measurements should be made as the data are extremely valuable in test evaluation.
There are several advantages of measuring the hydrogen flux:
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9.5
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•
a comparison can be made with field data (if available) to confirm correct
severity of test;
•
a comparison can be made with existing data; and
•
the effect of galvanic coupling on hydrogen permeation can be assessed for the
two parent materials in a girth weld.
Test duration and solution monitoring
The full ring test duration shall be 30 days.
NOTE 1 If the test environment has been reduced in severity from options a) or b)
in accordance with 5.4,extended test duration may be considered.
NOTE 2 On-line monitoring by ultrasonic and hydrogen permeation measurements
may be used to indicate if an extended test duration is required.
The H2S concentration in solution shall be checked regularly and, for options a)
and b), in accordance with 5.4 maintained at 2 300ppm or greater. The H2S
analysis is very important and should be carried out in accordance with Annex E.
The analysis shall be undertaken daily until the recommended H2S concentration
is reached and every five days thereafter until completion of the test. All data
shall be recorded. The pH shall be measured at the same time as the H2S
sampled.
The full ring test cell shall be controlled at a temperature of (24 ± 3)°C
[(75 ± 4)°F] unless otherwise stipulated by the client. For lined and corrosion
resistant alloys temperature shall be stipulated by the client.
9.6
Test commencement
The test environment shall be introduced after ultrasonic inspection, loading,
sealing and purging with deaeration gas to meet the oxygen concentration
requirements in accordance with 9.3.
Before filling with this solution, the test cell shall be checked for leaks. If the
test cell is gas tight the prepared solution shall be transferred from the mixing
tank to the test cell under a blanket of deaeration gas.
The test gas shall then be introduced into the cell. Continuous bubbling is
required throughout the test duration using an open ended gas inlet.
Tube with a diameter of not less than 5 mm shall be used.
Fritted end tubes shall not be used as they are liable to blockage by corrosion
product during testing.
The H2S concentration in solution shall be measured in accordance with the
procedure given in Annex E. When the H2S concentration reaches or exceeds the
target value in accordance with 9.5, the test shall be deemed to have
commenced.
NOTE 1
This concentration should be reached within 24 h.
NOTE 2 H2S is an extremely toxic gas and should be handled with care,
see Annex G.
9.7
On-line monitoring
The following inspections shall be undertaken during the test exposure:
•
ultrasonic inspection, reporting results every (7 ± 2) days, (see Annex A);
NOTE This inspection generally cannot be undertaken on small diameter pipes
which have been externally clamped.
•
analysis of H2S concentration in solution and pH measurement every five
days after the target has been attained;
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•
if hydrogen permeation cells are attached, a continuous reading e.g.
every 15 min, shall be recorded;
•
the temperature, gas flow and general condition of the test shall be
recorded twice daily.
NOTE 1
An example of a test record is provided in Annex H and Annex I.
NOTE 2 H2S is an extremely toxic gas and should be handled with care,
see Annex G.
9.8
Test cessation
After the full ring test has completed the agreed exposure period, the test cell
shall be drained and unloaded.
NOTE 1 It is recommended that the test solution be purged before draining to
assist in removing H2S and caution taken to ensure that the H2S concentration of the
resultant internal volume is below safe regulatory limits.
A final ultrasonic inspection shall then be undertaken and all indications
recorded, and locations marked on the test specimen. Indications shall be
characterized metallographically, the extent of such evaluation being agreed
with the client. In addition if no indications are found by NDT then the highly
stressed regions shall be examined metallographically in a minimum of two
locations (one from each high stressed area).
NOTE 2 Features associated with this test method are generally revealed at
magnifications up to 400x.
NOTE 3 Magnetic particle inspection (MPI) should be undertaken in accordance
with Annex N.
10 Expression of results
The following data shall be reported:
•
test conditions and loading recorded using Form 1 (see Annex H);
•
pipe dimensions, material identification and loading recorded using
Form 2 (see Annex I);
•
ultrasonic inspection records as specified by the authority undertaking the
inspection. The minimum level of reporting in accordance with Annex A,
shall be used as a mandatory inspection level;
•
metallographic inspection of indications shall be described and evaluation
undertaken, where so agreed;
•
a summary report, detailing pipe dimensions, material identification,
loading, H2S concentrations throughout the test and dates of ultrasonic
inspections is recommended (see Annex H and Annex I).
NOTE
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See Annex J for suggested acceptance criteria.
© The British Standards Institution 2016
BRITISH STANDARD
Annex A
(normative)
A.1
BS 8701:2016
Ultrasonic examination of pipe, plate and welds
during accelerated laboratory tests
Introduction
NOTE 1 Pipelines transporting hydrocarbon fluids could be prone to develop
hydrogen pressure induced cracking (HPIC). This normally occurs in the mid-wall
section of the pipe plate, and through a series of steps, cracking can become surface
emerging.
NOTE 2 Cracking also occurs in the circumferential butt weld, usually transverse,
and eventually becomes surface emerging.
NOTE 3 The longitudinal weld can develop toe cracks usually emanating from the
internal surface.
NOTE 4 The non-destructive testing (NDT) method considered most appropriate for
early crack detection is ultrasonic.
In view of the multiple possible crack orientations, both zero degree
compression and angle shear wave scans shall be used.
Figure A.1
Most common crack locations
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A.2
Purpose
This procedure defines the ultrasonic method and the requirements to be
followed for the inspection of pipe, plate and weld during an accelerated
operating test.
A.3
A.3.1
General requirements
Personnel
The examination shall be performed by personnel qualified in accordance with
BE EN ISO 9712. In addition to knowledge of ultrasonic testing, personnel shall
also be familiar with testing problems specifically associated with the type of
cracking to be selected.
A.3.2
A.3.2.1
Equipment
Ultrasonic flaw detectors
Equipment shall conform to BS EN 12668 (all parts).
A.3.2.2
Ultrasonic probes
Ultrasonic probes shall conform to BS EN 12668-2 and BS EN 12668-3.
A.3.2.3
Zero degree compression probes
Single and/or combined double crystal compression wave probes shall be used.
They shall have a crystal size ranging from 10 mm to 20 mm and a frequency in
the range of 4 MHz to 10 MHz.
Exact probe details shall be specified in the individual report sheets and
technique sheets.
A.3.2.4
Angle shear wave probes
Single and/or combined double crystal 45°, 60° and 70° shear probes shall be
used. They shall have a crystal size of 10 mm and a frequency in the range
of 4 MHz to 5 MHz.
Exact probe details shall be specified in individual report sheets and technique.
A.3.2.5
Calibration reference blocks
The following calibration and reference blocks shall be prepared from a sample
of the pipe material in accordance with:
A.3.2.6
•
BS EN ISO 7963, Block No.2 (IIW-V2); and
•
BS EN ISO 2400, Block No.1 (IIW-V1).
Flaw location aids
Suitable flaw location equipment such as slides shall be available and used at
the time of testing.
A.3.2.7
Couplant
The couplant used shall be silicone-free and shall not adversely affect the strain
gauge adhesion. The coupling media shall be in accordance with
BS EN ISO 16810. The coupling medium used for range and sensitivity setting
and for the test shall be the same.
NOTE Couplants containing silicone have been found to adversely affect adhesion,
leading to inaccurate strain response.
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A.3.3
BS 8701:2016
Surface condition
All surfaces from which scanning is to be carried out shall be prepared such that
satisfactory acoustic coupling can be achieved for the full scan distance. To
achieve this, the scanning surface shall be free from loose oxide scale, weld
spatter and other surface irregularities.
The entry and back surfaces of the component shall be sufficiently smooth to
maintain a first back wall echo amplitude of greater than 50% full screen height
while scanning an area which does not contain significant reflectors.
No weld dressing shall be permitted without prior agreement of the client. The
scanning surface finish of the item under examination shall be 6.3 micrometre
Ra (250 microinches CLA) or finer.
NOTE
A.3.4
This can usually be achieved by gritblasting.
Scope of examination
A.3.4.1 The ultrasonic examination shall be performed on the pipe prior to test
commencement and during the test at regular intervals.
A.3.4.2 The weld volume, heat affected zone and adjacent parent material shall
be scanned using zero degree compression wave techniques where possible.
A.3.4.3 The entire weld volume, including the heat affected zone and also any
regions in the parent plate where indications have been detected by the zero
degree compression wave technique, shall be examined using angle shear wave
technique.
A.4
A.4.1
Examination procedure
Weld examination
Unless otherwise requested, the weld examination shall be performed in
accordance with BS EN ISO 17640. In accordance with A.3.4, the weld cap shall
not be dressed without prior agreement of the client.
A.4.2
Determination of scanning sensitivity – zero degree compressional
wave
A.4.2.1 The scanning sensitivity shall be defined by the reference level plus 6 dB.
A.4.2.2 The reference level shall be set on an area of the base material free from
imperfections such that the second backwall echo is displayed at full screen
height.
A.4.2.3 Alternative method if requested, using a standard reference block
containing flat bottomed/side drilled holes at a depth nominally equal to or
greater than the product thickness, at one half (\2) and one quarter (\4) of the
product thickness can be used; the standard reference blocks shall be of the
same material as the component tested.
A.4.2.4 A distance amplitude curve (DAC) shall be constructed using the standard
reference block. The reference level shall be based on the DAC curve.
A.4.2.5 When the reference block is different from the test component, a
transfer correction shall be considered. This shall be carried out in accordance
with BS EN ISO 17640.
A.4.3
Determination of scanning sensitivity – angle shear wave
A.4.3.1 The scanning sensitivity shall be determined using the reference blocks as
described in A.4.2.3 containing side drilled holes at a depth nominally equal to
or greater than the product thickness.
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A.4.3.2 The scanning sensitivity shall be set such as the maximized signal echo
from the side drilled hole at a depth of product thickness is set at full screen
height plus 6 dB.
A.4.3.3 Alternatively a reference level based on a DAC curve can be used; the
construction of the DAC curve shall be carried out in accordance with
BS EN ISO 17640.
A.4.3.4 When the reference block is different from the test component, a
transfer correction shall be considered. This shall be carried out in accordance
with BS EN ISO 17640.
A.4.3.5 The scanning sensitivity shall be set at DAC reference level plus 6 dB.
A.5
A.5.1
Scanning
Zero degree compression wave – base material examination
The entire external surface of the pipe plate shall be examined in two directions
using compression wave techniques to detect imperfections and also to ascertain
the exact wall thickness of the material.
Any imperfections within the volume of base material, through which angle
shear wave examinations are to be carried out, i.e. an area of 5.5 times the
material thickness plus 30 mm on each side of the weld, shall be noted.
A.5.2
Zero degree compression wave – weld volume examination
The weld volume and heat affected zone shall be examined using zero degree
compression wave techniques where access, surface condition and weld
configuration allow in order to ensure complete coverage. In accordance with
A.3.4, the weld cap shall not be dressed without prior agreement of the client.
A.5.3
Angle shear wave – base material examination
Scanning of base material shall be carried out where imperfections were found
by zero degree compression wave technique and shall be carried out using angle
beam search units of at least two different refracted angles. The differences
between the angles shall be at least 15°, normally 45°, 60° and 70° refracted
angles being used.
The scanning shall be carried out to determine whether the imperfections are
laminar or stepwise.
A.5.4
Shear wave – weld volume examination
Scanning of welds shall be carried out in accordance with BS EN ISO 16810 and
BS EN ISO 17640.
A.6
A.6.1
Evaluation of indications
Zero degree compression wave
Evaluation of indications shall be performed at reference level.
Maximum signal amplitude equal of exceeding 15% full screen height at
reference level shall be evaluated.
A.6.2
Angle shear wave
Indications presenting maximum signal amplitude greater or equal to the
evaluation level defined in accordance to BS EN ISO 11666 shall be evaluated in
accordance to BS EN ISO 17640.
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A.7
BS 8701:2016
Acceptance and recording standards
A factual report detailing all indications having a response in excess of the
recording level defined in BS EN ISO 11666 shall be produced in accordance to
BS EN ISO 17640.
A.8
Reporting
The examination report shall contain at least the information specified in
BS EN ISO 16810 and BS EN ISO 17640.
A.9
Deviation
If the NDT operative is unable to comply with this procedure, then guidance
shall be sought from the client. Any agreed deviation shall be documented and
referenced for NDT departmental records.
Annex B
(normative)
Ring loading
COMMENTARY ON ANNEX B
This Annex incorporates the strain gauging technique as a means of pre-tensioning
full ring test specimens of 3 in. to 46 in. diameter prior to sour testing.
B.1
Introduction
A strain gauge is a precision device and the technique described shall be
conducted by competent personnel.
B.2
Ring specimens
Neglecting ring diameters; specimens fall into 8 categories which shall be
designated as:
a)
seamless specimens;
b)
specimens containing a longitudinal weld seam only;
c)
specimens containing a spirally wound weld seam only;
d)
specimens containing a girth weld seam only;
e)
specimens having either longitudinal or spirally wound weld seams
connected by a girth weld seam, wall thicknesses either side of the girth
weld seam being equal;
f)
as in e) but with wall thicknesses either side of the girth weld seam being
unequal;
g)
seamless specimens girth welded to specimens containing a longitudinal
weld seam, wall thickness either side of the girth weld being equal;
h)
as in g) but with wall thicknesses either side of the girth weld seam being
unequal.
Each of these cases shall be treated separately with regard not just to strain
gauging but also the mode of loading.
B.3
Load application
Load application shall be accomplished by one of two methods depending
principally on the diameter of the ring specimen under test.
For rings having a diameter of no greater than 12 in. (305 mm), the specimen
shall be loaded externally using the form of loading rig shown in Figure 2
NOTE This takes the form of two substantial loading blocks interconnected by six
loading screws that apply and distribute the load evenly.
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The specimen ring shall be placed between the loading blocks to achieve peak
tensile stress internally at the two points of contact with the blocks.
For ring specimens which are not less than 12 in. (305 mm) in diameter, the
typical form of rig shown in Figure 1 shall be utilized. In this rig, loading shall
be applied internally using a turnbuckle via two loading blocks. Here, loading
shall be applied 90° and 270° remote from the position of peak internal stress.
Due to ring specimen size, initial loading shall be applied through a hydraulic
jack situated below the turnbuckle. The turnbuckle shall then be tightened
before removing the hydraulic loading.
B.4
Loading rig treatment
Both forms of rig shall be designed for repeated use. At the conclusion of
chemical treatment of any ring specimen, any rig component that has been
submerged within the treatment area shall be thoroughly wire brushed and,
where practicable, submerged in oil until next required. On removal from the
oil, the components shall be degreased. At no time shall components of either
form of rig come into contact with copper (Cu) or molybdenum (Mo) greases.
B.5
Surface preparation of ring specimens
For the purpose of strain gauge application and subsequent chemical testing,
the internal surface of any ring specimen shall be grit blasted to Sa 2 1⁄2 using
Garnet (20-40 mesh) without recirculation. To reduce contamination through
oxidation, the pipe sample shall be stored under a dry atmosphere until loading
is performed.
NOTE
Alternative surface finishes can be agreed with the client.
Persons responsible for conducting surface processes on any ring subject to
subsequent strain gauge testing shall ensure that all products used in such
processes are free from silicone compounds.
All areas intended for subsequent strain gauge application shall be thoroughly
degreased using Propan-2-ol or similar degreasing agent.
Gauge positions shall be marked out initially using French chalk with the
markings extending approximately 100 mm beyond the gauge position in all
directions. An area approximately (25 × 25) mm centred on each gauge position
shall be lightly ground using a 180/240 grit wheel and then hand polished
using 320/400 grit. This latter operation shall be conducted using rotary motion
to prevent producing linear stress raisers. Where such positions encroach on
weld seams, it shall be ensured that the grinding and polishing extends across
the toe of the weld and on to weld metal. Such operations shall be completed
using light pressure to reduce introduction of residual stress.
Each gauge position shall then be finally marked out using a 2H grade pencil
and the positions additionally treated in the manner described by the gauge
manufacturer.
B.6
Strain gauges
Strain gauges of the electrical resistance foil type shall be used. Such gauges
shall be of 120 Ω nominal resistance and shall have nominal gauge lengths
of 1 mm for ring diameters of 6 in. or less and 2 mm for ring diameters greater
than 6 in.
NOTE 1
Other strain gauge lengths can be used with client agreement.
NOTE 2 For the purpose of static measurement, the following forms of gauge are
recommended:
18
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a)
single element;
b)
90° stacked rectangular/ T gauge/ biaxial;
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BRITISH STANDARD
BS 8701:2016
c)
45° stacked rosette.
The strain gauges shall be self-temperature compensated appropriate to the ring
test material and shall have stability within the range -10°C to +30°C.
Strain gauges shall be applied with one element orientated m the hoop axis of
the ring specimen.
The centres of gauge grids shall normally be positioned at a nominal distance
of 3 mm to 3.5 mm from the toe positions of any welds seams where
encountered.
B.7
Strain gauge adhesives
The adhesive used in strain gauge bonding to the test surface shall be
compatible with the applied gauges. It shall be of the cyano-acrylate type and
capable of withstanding strain levels of the order of 2% strain (20000 µƐ).
B.8
Strain gauge wiring
All wiring to strain gauges shall be made up from 3-core, 0.08 mm Cu/PVC
sheathed cable and connected to instrumentation using 3-wire quarter-bridge
configuration.
Principal output wiring shall be connected to composite gauge wiring via
suitable tab terminals.
Solders utilized shall be compatible with the applied strain gauges. All soldering
shall be free of solder spikes and cold joints and be cleared of any residual flux
on completion.
B.9
Strain gauge tests
All strain gauges shall, immediately following application, be checked with
a purpose-designed strain gauge installation test instrument to ensure that the
following are achieved or the gauge shall be replaced:
B.10
a)
nominal gauge resistance deviation is less than 1%;
b)
insulation resistance to earth exceeds 2 kMO;
c)
an effective bond exists at the gauge glue line.
Strain gauge data acquisition
After acceptance of strain gauge tests, the fitted gauges shall be connected to a
suitable strain gauge test instrument.
NOTE The instrument should be suitably calibrated and have a measurement
resolution of ±1µƐ.
B.11
Potential sources of loading errors
There are a number of factors that might introduce the following errors into the
loading system and due care shall be taken to reduce these to a minimum:
a)
misalignment of the loading blocks along the 90°/270° longitudinal axes of
the ring specimen;
b)
misalignment of the turnbuckle across the centreline of the girth weld
where present;
c)
off-centre guide cups in the loading blocks for location of the turnbuckle
screw heads;
d)
the loading blocks should be radiused to match the ring internal diameter
to reduce the tendency for blocks to dig into the ring wall and thereby
redistribute the overall stresses, over a period days, from loading;
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e)
where internal ring wall mis-match occurs, it is essential to produce accurate
shimming between the ring wall and loading blocks to prevent
redistribution of stresses with time as in d);
f)
misalignment of strain gauges in respect to the ring longitudinal and
circumferential axes;
g)
use of incorrect instrument gauge factor settings and the gauge factors of
the strain gauges used. This includes the use of strain gauges where the
stipulated gauge factor is only quoted as ’nominal’ and it is recommended
that such gauges are not used in full ring testing;
h)
settlement of load distribution about the threads of the turnbuckle
following loading will tend to relax load at the loading blocks and, hence,
also throughout the ring.
These are the principle areas that might cause serious error and great care shall
be taken in reducing these to a minimum when undertaking loading of ring
specimens using the strain gauge technique.
B.12
B.12.1
Strain gauge positions on full ring specimens (internal)
General
Eight forms of ring specimen are described in this Clause wherein the minimum
number of gauges which shall be used in order to achieve acceptable
pre-loading within the agreed bounds of experimental error are described.
B.12.2
Seamless specimens
Biaxial gauges shall be located as shown in Figure B.1, along the central
circumference of the ring.
Figure B.1
Key
1
2
3
4
5
20
•
Gauge positions for seamless ring specimens
T = 90° Rectangular, S = Single
Gauge 1T
Gauge 2T
Optional gauges S
Internal view
© The British Standards Institution 2016
BRITISH STANDARD
BS 8701:2016
NOTE Where doubt exists as to the position of loading points in relationship to the
target (0°) pre-tensioning zone, it might be necessary to apply two single element
gauges; one either side of one of the 90° rectangular gauges so that any imbalance
can be quickly observed and rectified by repositioning the applied load. These added
gauges should be equidistant from, and within 25 mm of the 90° rectangular gauge,
and applied in the same circumferential axis.
B.13
Longitudinal weld seam specimens
Gauges of the 90° rectangular type shall be positioned as shown in Figure B.2,
on the central circumference of the ring.
Figure B.2
Key
1
2
3
4
5
Gauge positions for ring specimens that contain only a longitudinal seam weld
T = 90° Rectangular, S = Single
Gauge 3T
Gauge 1T
Gauge 2T
Optional gauges S
6
Internal view
NOTE 1 ln this form of ring specimen, gauges are again located in the central
circumferential axis.
The target pre-tensioning position (0°) shall lie immediately to one side of the
longitudinal seam toe of weld.
NOTE 2 Again, where there are any doubts as to position of loading points in
relationship to the target pre-tensioning zone, then the additional single element
gauges should be applied in the 180° axis equi-spaced not greater than 25 mm
either side of the 90° rectangular gauge.
B.14
Spirally wound weld seam specimens
Ring specimens of the spirally wound form might still be encountered and here
a combination of 90° rectangular and 45° rosette type gauges shall be used as
shown in Figure B.3.
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BS 8701:2016
Figure B.3
Key
1
2
3
4
5
BRITISH STANDARD
Gauge positions on specimens having a spirally wound seam only
T = 90° Rectangular, R = 45° Rosette
Gauge 1R
Gauge 6T
Gauge 4T
Gauge 3R
B.15
6
7
8
9
Gauge 7T
Gauge 5T
Gauge 2R
Internal view
Girth weld seam specimens
Usually confined to ring specimens of small diameter, gauges of the 90°
rectangular form shall be used at positions shown in Figure B.4.
NOTE Doubts might arise as to the position of loading points relative to the target
(0°) pre-tensioning zone. Where practicable, additional single element gauges may
be placed as shown, but this will depend upon available space for such gauges to be
applied at less than 15° either side of the datum.
Figure B.4
Key
1
2
3
4
22
•
Gauge positions for ring specimens that contain only a girth weld seam
T = 90° Rectangular, S = Single
Option gaugesS
Gauge 1T
Gauge 3T
© The British Standards Institution 2016
5
6
7
Gauge 2T
Gauge 4T
Internal view
BRITISH STANDARD
B.16
BS 8701:2016
Girth weld specimens combined with longitudinal or spiral
welds – all plates of identical wall thickness
This form of ring specimen has a wide variety of geometries as shown in
Figure B.5, Figure B.6, Figure B.7 and Figure B.8. In general, the longitudinal
weld seams can be displaced by between 30° and 180°.
In some cases, the secondary weld seam might come into contact with one of
the loading beams. In such cases it is necessary to grind back the weld cap of
the longitudinal weld seam flush with the internal ring surface.
Figure B.5
Gauge positions for ring specimens that contain both circumferential and longitudinal
weld seams and have an angular gap of between 5° and 175° between longitudinal seams
Key
1
2
3
4
5
6
7
Gauge 1T
Gauge 2T
Optional 3S
Gauge 4T
Optional 5S
Gauge 6T
Gauge 7T
NOTE
Gauges are of the 90° rectangular type except for single element optionals.
8
9
10
11
12
13
40° / 70° Typical
Optional 8S
Gauge 9T
Optional 10S
Internal View
T = 90° Rectangular , S = Single
Should the angular gap between longitudinal weld seams be of the order of 0°
to 5° or 175° to 185°, then additional gauging in the target zone (and
about 180°) shall be provided as shown in Figure B.6.
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BS 8701:2016
Figure B.6
Key
1
2
3
4
5
6
7
BRITISH STANDARD
Modified gauge positions for ring specimens that contain both circumferential and
longitudinal weld seams and have an angular off-set of <5° or 175° to 185° between
longitudinal weld seams
T = 90° Rectangular
Gauge 1T
Gauge 9T
Gauge 7T
Gauge 5T
Gauge 3T
Gauge 2T
8
9
10
11
12
13
Gauge 10T
Gauge 8T
Gauge 6T
Gauge 4T
0° to 5° Typical
175° to 185° Typical
NOTE Gauges 3 and 4 stand for all cases. If welds overlap, gauges 7 and 10 may be omitted. If secondary weld
overlaps 180° then gauges 5 and 6 are omitted and gauge 3 lies on the 180° axis.
In the case of the spirally wound specimens containing a girth weld seam,
gauging as shown in Figure B.7 shall be applied.
Figure B.7
Gauge positions on specimens having spirally wound weld seams combined with a girth
weld
Key
1
Gauge 3R
2
Gauge 1R
3
Gauge 11T
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8
9
10
© The British Standards Institution 2016
Gauge 2T
Gauge 12T
Gauge 10T
BRITISH STANDARD
BS 8701:2016
Figure B.7 Gauge positions on specimens having spirally wound weld seams combined with a girth
weld
4
5
6
7
Gauge 5T
Gauge 7T
Gauge 9T
Gauge 4T
11
12
13
14
B.17
Gauge 8T
Gauge 6T
Internal view
T = 90° Rectangular, R = 45° Rosette
Girth weld specimens combined with longitudinal spiral
welds – plates of unequal wall thickness
NOTE Occasionally, risers and similar sections come under test and, in such cases,
the thickness of ring sections either side of the girth weld seam can vary
considerably. In most cases with this form of girth juncture, the ring wall thickness
difference is taken upon the internal bore diameter. Hence the internal ring wall is
stepped. In some cases this step is unequal, which gives rise to different widths of
gap behind the loading blocks at the larger inside diameter ring.
Packer shims of correct thickness shall be produced for behind each loading
block to ensure an even distribution of load throughout the ring assembly.
Figure B.8
Key
1
2
3
4
5
6
7
8
NOTE
Gauge positions for ring specimens that contain both circumferential and longitudinal
weld seams where individual plates are of unequal thickness
Thin plate
Gauge 3T
Gauge 1T
Gauge 11T
Gauge 10T
Gauge 8T
Gauge 6T
Gauge 4T
9
10
11
12
13
14
15
16
T = 90° Rectangular
Gauge 2T
Gauge 12T
Gauge 9T
Gauge 7T
Gauge 5T
Thick plate (sometimes seamless)
Internal view
Gauges are 90° rectangular type throughout.
B.18
Seamless rings combined with longitudinal weld specimens
These are essentially similar to the case just described. In the case of rings
having similar thickness refer to Figure B.8 and omit or optionally use
gauges 3, 4, 5, 8, 9 and 10 using single element gauges. For rings of dissimilar
thickness employ Figure B.8 without change.
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B.19
Ring pre-tensioning stress/strain calculations
These are principally as shown on the specimen data record sheet included at
the end of this procedural document.
NOTE The data record sheet provided is “tentative” only and at present test data
and diagrams of the ring and strain gauging are provided in accordance with
individual test needs.
It has been shown that the strain at the 0° and 180° axes can increase with time
under constant load by as much as 2% where the pre-tensioning load is set
at 72% specified minimum yield strength (SMYS). Where higher pre-tensioning
values are set, this factor shall be taken into consideration.
The actual loading level shall be defined by the purchaser and test agency
bearing in mind ultimate design requirements. In general, however, load levels
fall into the ranges given in Table 1 and are dependent upon final use.
Table B.1
Load level ranges
Load level
%
30
60
72
B.20
Range
On land
Risers
Offshore
Reporting of ring specimen loading
Principal dimensional information, together with material properties of the ring
specimen undergoing loading shall be provided. Such information shall be
produced on a Full Ring Testing - Loading Data Sheet. The form shall also detail
the required pre-tensioning level and provide for the required calculation of
strain required to achieve this. An opened- out plan of the internal ring surface
shall be provided so that weld detail can be outlined, together with gauge
positions and numbering. A section shall be provided so that all strain gauge
readings can be tabulated, together with final calculations of principal hoop
strain and achieved stress levels. Finally, any procedural deviations shall be
recorded.
This form shall be accompanied by copies of certification for applied strain
gauges.
NOTE
B.21
An example is shown in Annex H.
Secondary testing
NOTE 1 On occasions it is necessary to re-test a ring specimen at a higher
percentage of SMYS. To carry out such a procedure requires reapplication of the
strain gauges after suitable surface re-preparation, followed by the complete
off-loading of the ring. After off-loading, it is usual to find some degree of
permanent set in the ring, indicating the introduction of permanent residual strain.
The degree of residual surface strain shall be evaluated prior to a re-loading.
NOTE 2 It is unlikely that any significant residual strain will be present in the
longitudinal axis of the ring and, therefore, single element strain gauges may be
used at all positions originally gauged during loading.
Surfaces shall, be thoroughly cleaned and prepared prior to gauge application.
On removal of the load, the strain values obtained at each gauge shall be noted
and, in final re-loading, such values removed from the calculated strain levels
required to attain the new percentage SMYS. Separate test result sheets shall be
produced for both the off-loading and re-loading phases when issuing the final
report.
26
•
© The British Standards Institution 2016
BRITISH STANDARD
Annex C
(informative)
BS 8701:2016
Typical internal and external load application rigs
for use in the full ring test
Figure C.1 shows the external loading blocks used for ring specimens
below 305 mm in diameter.
Figure C.2 shows the loading rig for the full ring test.
Figure C.1
External loading blocks used for ring specimens below 12 in. (305 mm) in diameter
Key
1
Loading block with M23 tapped holes
2
Radius longitudinal slot on inside face of both loading blocks having a radius of 1.2 times the
anticipated maximum ring diameter to be loaded
3
Ring specimen
4
M23 H.T. bolts screwed full length
5
Loading block with M23 clearance holes for bolt insertion
© The British Standards Institution 2016
•
27
BS 8701:2016
Figure C.2
Key
1
2
3
4
BRITISH STANDARD
Internal loading rig used for ring specimens above 12 in. (305 mm) in diameter
Pipe inside diameter >300mm
Closed jack position
Load beam
Turnbuckle
Annex D
(normative)
D.1
5
6
7
8
Weldment
Hydraulic jack
Spacer block
Height adjustable supports
Chemistry of test solutions
NOTE As acetic acid (and thio compounds such as thioacetic acid) are volatile, care
should be taken not to lose them during deaeration.
NACE TM0177 solution A
The solution composition for NACE TM0177 [N1] shall be as given in Table D.1.
28
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© The British Standards Institution 2016
BRITISH STANDARD
BS 8701:2016
Table D.1 – Standard NACE TM0177 solution A composition
Chemical
in 1 kg solution
g
sodium chloride
acetic acid
distilled water
50
5
945
D.2
Method of preparation
Distilled water shall be deaerated with nitrogen for at least 24 h. Into this water
the correct amounts of sodium chloride and acetic acid shall be added. These
reagents shall then be dissolved and dispersed into the water with as little
turbulence as practically possible. The solution shall then be deaerated with a
slow bleed of nitrogen for 30 min.
NOTE
D.3
The pH of the resultant solution should be 2.7 to 2.9.
Highly buffered solution composition
The solution composition for the highly buffered solution shall be as given in
Table D.2.
Table D.2 – Highly buffered solution composition
Chemical
Amount in the 1 kg solution
g
sodium chloride
acetic acid
distilled water
50
50
900
D.4
Method of preparation
The highly buffered solution shall be prepared in accordance with D.2.
NOTE The initial pH of this solution is lower than that of NACE solution due to the
larger amount of acetic acid, but its pH can be raised by sodium hydroxide or
sodium acetate additions to a level of 3.2.
D.5
Saturation with H2S
The solutions shall be saturated with H2S.
NOTE
This is best achieved in situ in the test cells or pipes.
The temperature of the solution shall be maintained at (24 ± 3)°C [(75 ± 4)°F]
throughout the test period.
Annex E
(informative)
E.1
Analysis of test solution – iodimetric titration
procedure
General
An aliquot of H2S containing solution should be added to iodine solution. The
sulfide is oxidized to sulfur by the iodine and the residual iodine is titrated
against 0.05 N sodium thiosulfate. This enables calculation of the sulfide
content.
© The British Standards Institution 2016
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BS 8701:2016
BRITISH STANDARD
a)
Accurately measure the volume (about 10 mL) of the sample solution into
a 250 mL conical flask. A measuring cylinder (not a pipette) should be used
for this.
b)
Add the sample to a flask containing 10 mL of the standardized 0.1 N iodine
solution and mix thoroughly.
c)
Add about 1 mL of 10% hydrochloric acid.
d)
Titrate by adding 0.05 N sodium thiosulfate by means of a burette until a
pale straw colour is reached.
e)
Add about 1 mL of starch solution and mix to produce a dark blue colour.
Then titrate until this blue colour is just discharged.
parts per million of H2S =
17000
(a.b2c.d)
e
5
共a×b2c×d兲
3
×17000
(E.1)
where:
E.2
a
is normality of iodine;
b
is volume of iodine (mL);
c
is normality of sodium thiosulfate;
d
is volume of sodium thiosulfate (mL);
e
is volume of sample solution (mL).
Preparation of standard solutions
0.05 N sodium thiosulfate solution.
Dissolve 12.409 g sodium thiosulfate pentahydrate Na2S2O3.5H20 in 1 L of water.
Store in a dark glass bottle.
E.3
Standardization of iodine solution
The iodine solution should first be standardized as follows.
a)
Add l mL of 10% hydrochloric acid to 10 mL of a 0.1 N iodine solution.
b)
Titrate with 0.05 N sodium thiosulfate until the solution is pale straw colour.
c)
Add I mL of starch solution to produce a dark blue colour, and then titrate
until this colour is just discharged.
iodine normality =
0.05×
vT
10
(E.2)
where:
vT
Annex F
(informative)
30
•
is volume of thiosulfate
Illustrated summary of the full ring test procedure
The test method is summarized in a series of steps as listed in Table F.1, together
with Figure F.1 to Figure F.12 that assist understanding.
© The British Standards Institution 2016
BRITISH STANDARD
Table F.1
BS 8701:2016
List of full ring test procedure figures
Step
Description
Figure number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Machine ring ends to provide clean flat ends
Grit blast to required finish
Full pre-test ultrasonic inspection
Strain gauge inside surface
Apply internal load
Convert ring into test cell
Position in secondary safety tank
Affix hydrogen permeation cells
Purge ring with nitrogen
Fill ring with deaerated solution
Charge with H2S gas, monitor H2S level by sampling
Ultrasonically inspect at approximately 7 day intervals
After 30 days, drain ring and unload
Final ultrasonic inspection
Produce hydrogen permeation data
Metallographically examine any significant ultrasonic indications. There are
four main type of crack illustrated in Figure F.10 to Figure F.13.
F.1
F.1
—
F.2
F.3
F.4
—
—
—
—
—
F.5
F.6
F.7
F.8
F.9, F.10, F.11 and
F.12
Figure F.1
Ring machined and grit blasted
© The British Standards Institution 2016
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31
BS 8701:2016
Figure F.2
Ring strain gauged
Figure F.3
Application of internal and external loads
a) Application of internal load
32
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© The British Standards Institution 2016
BRITISH STANDARD
BRITISH STANDARD
Figure F.3
BS 8701:2016
Application of internal and external loads
b) Application of external load
Figure F.4
Conversion of ring into test cell
© The British Standards Institution 2016
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33
BS 8701:2016
Figure F.5
On-line ultrasonic inspection
Figure F.6
Full ring after test
34
•
© The British Standards Institution 2016
BRITISH STANDARD
BRITISH STANDARD
Figure F.7
Figure F.8
BS 8701:2016
Example of ultrasonic indications after test
Example of recorded permeation data
Key
X
Time (hrs)
Y
Mico amps/cm2
© The British Standards Institution 2016
•
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BS 8701:2016
Figure F.9
36
•
Typical HIC crack
© The British Standards Institution 2016
BRITISH STANDARD
BRITISH STANDARD
Figure F.10
BS 8701:2016
Typical weld SSC
Figure F.11
Typical soft zone crack
© The British Standards Institution 2016
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BS 8701:2016
Figure F.12
BRITISH STANDARD
Typical SOHIC
Annex G
(informative)
G.1
Hydrogen sulfide (H2S) health and safety
considerations
General
Hydrogen sulfide is a colourless gas with a strong characteristic odour of rotten
eggs. Other chemical and physical properties of hydrogen sulfide are listed in
Table G.1.
Table G.1
Chemical and physical properties of hydrogen sulfide
Chemical and physical category
Property
Molecular weight
Specific gravity
Melting point
Boiling point
Flammable limits in air
Auto ignition temperature
Vapour pressure
Solubility
Weak acid
34.08
1.19 (air-1)
-82.9 °C
-60.33 °C
4.3% – 45% (by volume)
260 °C
17.38 bar (g)
437 mL in 100 mL water @ 0°C 180 mL in I 00 mL water @ 40°C
H2S↔HS2 1 H1 pKa = 6.88
HS2↔S2−+H1 pKa = 14.15
38
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© The British Standards Institution 2016
BRITISH STANDARD
BS 8701:2016
Dry hydrogen sulfide is not particularly reactive to common metals. It is much
more reactive at higher temperatures and moist conditions, and the presence of
carbon dioxide also increases the reaction rate. It forms characteristic shallow
pits and can induce various forms of cracking in steels.
G.2
Potential physiological effects of working with hydrogen
sulfide
Hydrogen sulfide is an extremely toxic substance and working with it needs
careful planning, monitoring and control.
NOTE Attention is drawn to the Control of Substances Hazardous to Health
Regulations 1988 (COSHH) [2] for the use of hydrogen sulfide in the workplace.
Additional information on the toxicity of hydrogen sulfide can be obtained by
consulting the Material Safety Data Sheet provided by the manufacturer or
distributor and from consulting sources such as Dangerous Properties of
Industrial Materials [3].
G.3
Fire and explosion hazards
Hydrogen sulfide is a flammable gas, yielding poisonous sulfur dioxide as a
combustion product. Sulfur dioxide is the result of combustion in air.
Appropriate precautions should be taken to prevent these hazards from
developing.
A secondary containment chamber should be used for conducting full ring tests.
However, for large diameter sections, where a large volume of H2S saturated
liquors are used, a separate safety enclosure, sealed from leaks and monitored,
should be used.
Annex H
(informative)
Figure H.1
Sample identification and test record, Form 1
Figure H.1 is the sample identification and text record (Form 1) that can be used
for data recording.
Sample identification and test record, Form 1
SAMPLE IDENTIFCATION AND TEST RECORD
(SOUR) DATE:………..
Job No.
Company
Ident
Project Name
Type of Test
Welds Present
L
Client & Source
No. of Samples
Wall Thickness
Sample
Width
Sample
Thickness
Test Material
Sample
Length
Load/Stress
Level
Client Ident
Sample
Height
Sample OD
Test Duration
Start pH
G
H2S Concentration
Test Solution
H2 Permeation
Cell Type
Gas Line In
Gas Flow Rate mL/min
Gas Line
Out
Test
Location
N2 On
Temperature
Solution
In
H2S
On
Blow
Down
© The British Standards Institution 2016
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BS 8701:2016
BRITISH STANDARD
Figure H.1 Sample identification and test record, Form 1
SAMPLE IDENTIFCATION AND TEST RECORD
(SOUR) DATE:………..
ULTRASONIC SURVEYS
Survey
Date
Initial
1
2
3
4
FINAL
By
H2S and Ph Levels
Date
H2S
pH
Date
H2S
pH
Comments
Annex I
(informative)
Figure I.1
Sample identification and test record, Form 2
Figure I.1 is the full ring test loading data sheets (Form 2) that can be used for
data recording.
Full ring test loading data sheets, Form 2
FULL RING TEST - LOADING DATA SHEETS
JOB REFERENCE:
CLIENT:
ITEM IDENTITY:
TEST DATE:
40
•
TEST AGENCY: INTERNAL
STAFF/CONSULTANCY
PRINCIPAL RING DIMENSION BEFORE AND AFTER LOADING
© The British Standards Institution 2016
BRITISH STANDARD
Figure I.1
BS 8701:2016
Full ring test loading data sheets, Form 2
DIMENSION
METRIC
IMPERIAL
RING SPECIMEN DEFECTS AND/OR
REPAIRS
DT
DB
TT
TB
H
W1-W2
CE
W1i
W1e
W2i
W2e
Lmax
Lmin
RING LOADING WAS BY INTERNAL TURNBUCKLE/ETERNAL LOADING PLATES
LOADING INSTRUCTIONS: Load to % of SMYS or
NOMINAL
0.2% YIELD
RING
STRENGTH (MPa)
VALUES
YOUNG’S MODULUS
(GPa)
CERTIFIED VALUES
POISSON’S RATIO
MATERIAL
PROPERTIES
From the above data,
STRESS STRAIN CALCULATIONS
% SMYS is equivalent to MPa
This is the principle hoop stress (σp )which is derived from the formula:
Principle hoop stress 共σp兲 5
E
1−v2
×(E1+vE2)
(I.1)
Where E is the Young’s Modulus, v is Poisson’s Ratio and E1 and E2 are the measured strain level
values at 90° rectangular type strain gauge placed in the hoop and longitudinal axes respectively.
Hence, the principal hoop strain required 共E1 + vE2) or Ep is given using the formula:
Principle hoop strain Ep=
1−v2σP
E
(I.2)
which in this instance computes to a value of µε
In some instances, it is required to load the ring specimen to give a nominal hoop stress based upon a
stipulated internal pressure.
In such cases, the following formula may be used to compute the principle hoop stress required:
Principle hoop stress 共σp兲 5
pD
2t
(I.3)
Where p is the quoted internal pipe pressure, D is the diameter of the ring and t is the ring wall
thickness.
In meeting this load requirement, the principle hoop stress has been computed to a value of
…….MPa. Substituting this value in the Formula (I.2) above, the principle hoop strain computes to a
value of µε .
© The British Standards Institution 2016
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41
BS 8701:2016
Figure I.1
BRITISH STANDARD
Full ring test loading data sheets, Form 2
STRAIN GAUGE POSITIONS AND NUMBERING
GAUGE
NO.
TABLE OF PRETENSIONING STRAIN LEVELS REACHED AT EACH GUAGE POSITION
GAUGE
ANGLE
RECORDED STRAIN (%)
PRETENSIONING AS%
TYPE
FROM 0°
OF SMYS
WELD
HOOP
45°
LONG
(%)
AXIS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
PROCEDURAL DEVIATIONS AGREED BY THE PRINCIPALS
DEVIATION NO.
DESCRIPTION OF PROCEDURAL DEVIATION
DATED
SIGNATURE
DEVIATION NO.
DESCRIPTION OF PROCEDURAL DEVIATION
DATED
SIGNATURE
DEVIATION NO.
DESCRIPTION OF PROCEDURAL DEVIATION
DATED
SIGNATURE
DEVIATION NO.
DESCRIPTION OF PROCEDURAL DEVIATION
DATED
SIGNATURE
42
•
© The British Standards Institution 2016
BRITISH STANDARD
Figure I.1
BS 8701:2016
Full ring test loading data sheets, Form 2
DEVIATION NO.
DATED
SIGNATURE
DEVIATION NO.
DATED
SIGNATURE
DEVIATION NO.
DATED
SIGNATURE
Annex J
(informative)
DESCRIPTION OF PROCEDURAL DEVIATION
DESCRIPTION OF PROCEDURAL DEVIATION
DESCRIPTION OF PROCEDURAL DEVIATION
Acceptance criteria
COMMENTARY ON Annex J
The recommendations in this Annex apply to environments (a) and (b) but not (c)
(see 5.4).
J.1
HIC
A crack area ratio of 5% measured by ultrasonic techniques is acceptable. Levels
greater than this are to be open to discussion. If the cracks are laminar with no
stepwise component, a level of 15% can be accepted.
NOTE For internally loaded test pieces, the area occluded by the load distribution
blocks is not taken into consideration.
J.2
SSC
No SSC cracks greater than 0.5 mm·in depth (characterized as cracking not
pitting) to be allowed.
J.2.1
SOHIC
The evidence and growth of SOHIC is to be confirmed by metallographic
inspection. If SOHIC is proven, then the material is deemed to fail.
If the cracking level obtained is “borderline”, a fracture mechanics study is to be
undertaken to ascertain if the exhibited cracks are stable under continued
hydrogen charging conditions. This analysis will confirm acceptance or rejection
of the material under test.
Annex K
(informative)
Sulfide stress corrosion (SSC) and hydrogen
induced cracking (HIC)
Sulfide stress corrosion (SSC) requires the combined action of tensile stress
(residual and/or applied) and the corroding environment, namely wet H2S acting
upon a susceptible material. The tensile stresses can cause failure at levels well
below the yield stress of the material.
SSC failures in some alloys result from hydrogen embrittlement, but since the
hydrogen is produced by the reduction reaction balancing the oxidation reaction
(corrosion) in an aggressive aqueous environment containing dissolved hydrogen
sulfide, the phenomenon is deemed to be SSC. In some cases failure might be
the result of localized anodic corrosion processes where hydrogen might or
might not be involved.
Such failures might, at times, fall into the category of SSC even though their
cause might not be hydrogen.
© The British Standards Institution 2016
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BS 8701:2016
BRITISH STANDARD
HIC needs only the corrosive environment and the damage is induced in the
absence of stress.
In these cases where damage is due to hydrogen embrittlement, the hydrogen
ions are reduced to adsorbed atomic hydrogen, which in other systems might
predominantly combine to form molecular hydrogen that can then evolve from
the surface into the aqueous environment in gaseous form. However, absorption
of this atomic is enhanced in wet hydrogen sulfide and can have several effects
depending upon the composition and microstructure of the steel and the
characteristics of the environment.
The hydrogen evolution reaction takes place in two stages:
a) Stage 1: 2H1 1 2e2→2Hads (hydrogen ions reduced to adsorbed atomic
hydrogen); and,
b) Stage 2: 2Hads→H2(g) (evolved molecular hydrogen gas)
Each stage has its own activation energy and rate constant (K1 and K2
respectively) with the slower stage being the rate determining step of the
overall hydrogen evolution process. So, if Stage 2 becomes the controlling step,
then atomic hydrogen can accumulate at the surface to the extent where it
might induce diffusion into the metal crystals producing catastrophic results such
as embrittlement. The presence of sulfides tends to increase the concentration
of atomic hydrogen available. This reaction is brought about by the presence of
the HS–.ion which exists in equilibrium with the H2S: H2SPHS2 1 H1 .
The lattice spacing for iron alloys is such that hydrogen atoms are able to
diffuse through the lattice as an interstitial element. The rate of diffusion is
highly dependent upon temperature.
In cases of SSC, the hydrogen atoms diffuse into the steel and tend to migrate
to regions of high stress and high hardness. This then leads to interaction with
the strain field and results in cracking via hydrogen embrittlement (several
theories exist on the specific mechanism which is beyond the scope of this
document).
However, in other cases, hydrogen atoms tend to recombine at dislocations and
at non-metallic inclusions or voids within the steel lattice forming pockets of
molecular hydrogen gas under pressure. If the stresses created in the
surrounding steel cannot be relieved by movement of dislocations, fracture
occurs. There are many terms used to describe failures of this kind, including:
a)
hydrogen induced cracking (HIC);
b)
hydrogen pressure induced cracking (HPIC);
c)
blister cracking (HIBC); and
d)
stepwise cracking (SWC).
SOHIC is a combination of SSC and HIC and generally needs some element of
stress, together with the sulfide containing environment. SOHIC starts by the
initiation of hydrogen induced cracks referred to as “latent initiants”. These are
linked by secondary SSC across the wall thickness. SOHIC develops in the through
thickness direction across the wall.
SOHIC is most likely to occur close to a weld due to residual stress effects,
although coupling effects due to minor differences in chemistry might also be a
contributory factor.
44
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© The British Standards Institution 2016
BRITISH STANDARD
Annex L
(informative)
BS 8701:2016
Explanatory notes on test method: Galvanic
Coupling
During development and in a number of tests it has been noted that a galvanic
couple can be produced when two sections of pipe from different sources are
welded together to form the test piece, for example pipe/bend, pipe/flange,
pipe A/pipe B. It is therefore useful to note the relevant potentials of each
section by inserting a Luggin probe through the lid and measuring the free
corrosion potential along the length of the test specimen. These data are
particularly useful when the two half sections appear to behave differently.
NOTE See Figure L.1 for a typical example of potential change on a girth welded
sample.
Figure L.1
Typical example of potential change on a girth welded sample
Key
X
Location along length of test piece
Y
Potential
1
Weld location
Annex M
(informative)
Modified test procedure for externally loaded test
specimens (Diameter <12 in. [305 mm])
A modified technique has been developed for smaller diameter sections and is
applicable to sections of 12 in. diameter or less.
It is generally accepted that in sour service testing there is a minimum surface
area to volume ratio which should be achieved. This is nominally 5 cm3 volume
to 1 cm2 of surface area. If small diameter sections are to be examined this ratio
might not be achieved within the test specimen alone due to the surface area of
the turnbuckle and blocks. Therefore, a modified loading technique is
recommended in which the ring section is externally squeezed.
With the exception of the loading method all other parameters of the full ring
test remain unchanged.
© The British Standards Institution 2016
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45
BS 8701:2016
BRITISH STANDARD
For very small diameter sections of 6 in. diameter or below, it is advisable to
have a separate reservoir of test solution and slowly circulate the solution
around the test piece by means of a peristaltic pump. This ensures that sufficient
volume/surface area ratio is achieved.
NOTE The area of ultrasonic inspection is limited due to the presence of the
external clamping system.
Annex N
(informative)
Magnetic particular inspection (MPI) procedure
The procedure employed for MPI should be documented and carried out by
competent personnel, in accordance with BS EN ISO 9712.
NOTE See also all relevant national and international standards, e.g.
BS EN ISO 9934 (all parts).
All aspects of the procedure should be appropriate for the geometry of the pipe
being inspected and the procedure should be performance tested against a pipe
sample of comparable dimensions with flaws of known size. Details of the
performance test sample should be reported in the test report.
The MPI procedure should include the following:
46
•
a)
the lab should have a procedure;
a)
the procedure should conform to the appropriate standard;
b)
the operator should be competent to perform the tests;
c)
the procedure should be performance tested against a representative pipe
before each test specimen inspection;
d)
the performance test part should be reported together with the test results,
so there is a record of the “established” performance.
© The British Standards Institution 2016
BRITISH STANDARD
BS 8701:2016
Bibliography
Standards publications
For dated references, only the edition cited applies. For undated references, the
latest edition of the referenced document (including any amendments) applies.
Standards publications
BS EN ISO 9001, Quality Management Systems – Requirements
BS EN ISO 9002, Specification for Manufacture and Installation
BS EN ISO 9934 (all parts), Non-destructive testing – Magnetic particle testing
BS EN ISO 16811, Non-destructive testing – Ultrasonic testing – Sensitivity and
range settings
BS EN ISO 15156-3, Petroleum and natural gas industries – Materials for use
in H2S-containing environments in oil and gas production – Part
3: Cracking-resistant CRAs (corrosion-resistant alloys) and other alloys
ASTM A370, Standard Test Methods and Definitions for Mechanical Testing of
Steel Products
Other publications
[1] OTI 95 635, A test method to determine the susceptibility to cracking of
linepipe steels in sour service. HMSO: Norwich, 1996.
[2] GREAT BRITAIN. Control of Substances Hazardous to Health
Regulations 1988 (COSHH). London: The Stationery Office.
[3] Lewis, Richard J Sr. Dangerous Properties of Industrial Materials 12th edition.
Wiley-Blackwell, 2012.
© The British Standards Institution 2016
•
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