4S Group Conference
Stockholm
Wednesday 15th October 2014
A Training and Certification Standard
for Fusion Welding of PE Pipes
Edward Ingham (Exova Utilities)
Introduction
• Failure statistics for PE joints in the UK Water Industry
• Causes of failure of PE joints
• Auditing of the welding process
• On site assessment of weld integrity
Destructive testing
Non- Destructive Testing (NDT)
• Training and Development of a UK National Training Standard
UK National Mains Failure Database (NMFD)
• Analysis of UK NMFD indicates 3.5 failures/100km/year for PE
• Rates possibly higher as repairs made without reporting
• Failures of service pipes not included in database
• Observed failures are not always correctly reported
• Reporting protocols often adapted from those for metal pipes
Polyethylene Materials
•
Lessons learnt from problems with early low toughness materials
•
Early PE materials (service pipes water) suffered from poor slow crack growth
resistance
•
Continuous development of PE 80 and PE 100 materials since 1960s
•
Current PE materials have exceptional SCG and RCP resistance
•
PE 100 materials tested to requirements in excess of current standards
•
PE 100+ Association encourages high performance and consistency
•
Exova research indicates PE 100 lifetime >200 years
Standardisation for PE Pipes and Fittings
•
EN 12201 series of standards for PE pipe/fittings are satisfactory
•
Some UK WIS requirements covered in National Foreword
•
Certain areas are not adequately addressed
•
Fusion lengths specified for electrofusion are minimum
•
No tolerances for ovality of coiled pipes
•
No contamination test for electrofusion fittings (WIS 4-32-08)
•
Fittings >630mm (e.g. stub flanges not covered)
•
Important tests (e.g. AREL) not covered in standards for mechanical fittings
A
PV
C
ne
Ir
on
Ir
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th
as
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ye
C
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C
em
Po
l
D
st
sb
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Failures/100km/ Year
UK National Mains Water Failure Database (<300mm)
30
25
20
15
10
5
0
UKWIR Report: Large PE Trunk Main Failures
>300mm Diameter
16
Burst Rate (Failures/100km/Year)
14
12
10
8
6
4
These companies appear to
have the correct approach
2
0
J
I
F
K
H
E
M
D
L
Company
Extremely variable performance - How can this be improved?
Methods of Jointing of PE Pipe Systems
•
Butt Fusion Welding (Above ground)
•
Extremely reliable technique-historically extremely low number of failures
•
Electrofusion Welding (In trench)
•
More appropriate for installation in urban areas
•
More sensitive to site conditions- disproportionate number of failures
•
Failures due to misalignment, contamination, poor pipe surface preparation
•
Jointing of coiled pipes significantly more difficult than straight lengths
•
Mechanical Jointing (In trench)
•
Reliable technique, but failures do occur due to poor assembly
C
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nt
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Pi
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Pi
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Fe
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Lo
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itu
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um
Number of Failures (%)
UK National Mains Failure Database for Polyethylene
45
40
35
30
25
20
15
10
5
0
Butt Fusion Weld Failures
Extremely reliable technique
Failures extremely rare
• Contamination
• Pressure issues
• Insufficient heating
Heat Affected Zone in Weld
Excessive pressure
(single pressure)
Typical weld bead
Failure of Mechanical Fittings
B
A
Leakage
C
Mechanical Fittings -Correct Assembly
Good all round access to
clamp bands
On Site Welding Conditions
Suppliers’ ‘Vision’ of
a typical trench
The reality!
Manchester in Summertime
Causes of Failure – Misalignment
Causes of Electrofusion Failures –Scraping of Pipe
Poor scraping of pipe surface
Hand scraping can leave areas
of pipe surface intact
Mechanical scraping ensure consistent/even
removal of pipe surface
Causes of Electrofusion Failures -Contamination
Particulate contamination due
to poor site hygiene
Incorrect use of welding wipes
Correct use of welding wipes
Jointing of Coiled Pipes
Large forces required to
straighten pipe
Pipe ovality causes gaps
Two joints of potentially poor integrity
Solutions for Jointing of Coiled Pipes
Reduce ovality at manufacture
Inserts to correct ovality
Coil straightener to correct curvature
Assuring Good Workmanship
Train
Audit
Continuous
Improvement
Analyse
Test
Structured PE Competence Programme
PE competence programme containing three elements that together
address the root causes of poor joint quality
Recommended frequency
Awareness
Training
Site Assessment
On-site Joint Tests
Every 3 years
Every quarter
Every quarter
Issues Addressed


Use of incorrect equipment


Poor equipment maintenance


Lack of awareness & competence
Commercial or time pressures
Pipe and fittings issues




On-Site Joint Testing
Demonstrate
The implications of deviations from best
practice (misalignment, poor scraping,
etc)
Give Immediate Feedback
Provide advice on equipment and
procedures to ensure joint quality
Provide Positive Feedback
Where correct equipment and procedure
is used
Destructive Testing of Butt Fusion Welds
ISO and Gas Geometry
WIS 4-32-08
Force / Deflection Data: Ductile & Brittle Welds
160
140
Brittle
120
Ductile
Force (kN)
100
80
60
40
20
0
0
5
10
15
20
25
Displacement (mm)
30
35
Strength is equal, Energy (area under curve) is different
40
Assessment of Electrofusion Joints
Hydrostatic Pressure Tests
Double Cantilever Beam (DCB)
G
P
H
P
P
Cold Zone
Starter
Crack
F
F
Side Grooves to
‘encourage’ cracking
Shear Test – full or part samples!
Failure Modes of Electrofusion Couplers DCB Test
Ductile
Brittle
Mixed
Voiding
Destructive Testing of Electrofusion Joints
Site Audit Data
All joints made specifically for audit purposes
Welders were aware the joints would be tested
Destructive Testing of Electrofusion Joints
Production Joint Data
All joints taken at random from installed system prior to commissioning
NDT Testing of BF Welds (Very simple form)
Twist bead an inspect for signs of splitting
NDT Testing- Microwave (MW) Imaging
•
Material under inspection is bathed in
microwave energy of an essentially
constant frequency (≈ 25GHz)
•
Energy is reflected from each interface of
differing dielectric constants within
specimen
•
The reflected energy creates a resulting
signal measured in volts
General Probe Configuration
•
The resulting voltage is sampled at discreet
locations across sample to create an image
•
Volumetric inspection technology: will view
the entire thickness of the piece at once
Channel A & B are a ¼ wavelength apart
NDT (Microwave) Evaluation of PE joints
•
State of the art NDT methods available to inspect
plastic joints in the field
•
NDT techniques has been verified by mechanical
testing
•
Removes the need to cut out and destructively test
joints.
•
Immediate feed back regarding quality of joint.
•
Testing can be done on new or in-service
pipelines.
•
The system can be used in conjunction with current
site auditing practices to further improve the
reliability and quality assurance of PE joints in the
field.
•
Fast assessment of joints
NDT microwave results of butt fusion joints
PASS
FAIL
Assessment of Weld Quality using Voltage Threshold
NDT Phased Array Results for Butt Fusion Joints
Well fused region of EF joint
PA-UT Field equipment
Lack of fusion observed in EF joint
Issues with Current Training and Certification
• Some training courses based on UK WIS 4-32-08
• Lack of National standard causes inconsistencies in training and hence
competence
• Training is classroom based rather than under true site conditions
• All practical assessments use relatively small diameter pipes
• Practical assessments are on straight pipe and not coils
• Theory examinations too easy (everyone passes)
• No time limit before re-training/refresher training is required
• No system to address poor workmanship/or ensure corrective training is
taken
Stakeholders
• Water UK
• Water Utilities
• PE pipe and fittings manufacturers
• Welding equipment suppliers
• Installation contractors of PE pipes
• Training companies
• Engineering Contractors
Administration of Standard and Qualification
• Expert group to be set up by Water UK
• Will review effectiveness of training and make change if necessary
• National database holding qualifications- held by UKAS accredited body
• Accreditation body to be appointed by Water UK
Structure of Specification
Training
Area
EF1
(20-180mm)
EF2
(200-315mm)
Electrofusion


Butt Fusion
-
-
Service Pipes

Distribution Pipes
EF3
(≥355mm to
710mm)
BF1
(63-355mm)
BF2
(>355mm
to 900mm)
-
-
-


-
-
-
-





Straight Pipe





Coiled Pipe

-
-

-
Barrier Pipe

-
-

-
Co-extruded Pipes

Branch Saddles


Skinned Pipe


-
-
-
Range of Qualification
•
Standard will be for welding personnel and supervisors of welding personnel
•
Aim to make personnel self supervising
•
Supervisors retain status by continuous record of competency and on site
welding every 6 months
•
3 Qualifications for electrofusion and 2 for butt Fusion
•
Qualification will be modular (i.e. to gain EF3 a welder must hold a current
version of EF1 and EF2)
•
For EF>710mm and BF >900mm specialist training from the fitting/equipment
supplier and certificate of competence required
•
Qualification valid for a period 3 years
•
Training for Electrofusion Welding
Introduction
Health and safety relevant to the welding process and working in the field
Relevant standards (WIS 4-32-08)
Pressure rating and SDR rating for pipes and fittings
Correct storage for pipes and fittings
The consequences of producing a poor quality weld
The different types of PE (PE 80 and PE 100) and how these materials differ from Polypropylene and
Polyvinylchloride (PVC)
The effect of ovality and pipe end reversion
Techniques for destructive and non-destructive testing (NDT) of welds
Pupped bends and fittings (potential issues regarding clamping)
The commissioning pressure tests and pressure tests for electrofusion top tee and saddles
Importance of machine calibration and periodic checks on pipe surface preparation tools
Welding Equipment
Generator and use of power ratings relevant to the procedure being undertaken
Control box
Pipe surface preparation tools for conventional pipes, pipes with a peelable skin, barrier pipes and
coextruded pipes.
Pipe clamps for re-rounding and restraining pipes and positioning electrofusion tapping tees and saddles
Ancillary Equipment
Welding shelter, pipe support Rollers, coil straightening equipment.
Techniques for lifting of pipes, pipe cutters, PI tape, marker pen (for marking insertion depths)
Isopropanol cleaning wipes and pipe end plugs
Checking of pipe/ fittings (markings, damage or ovality)
Training for Electrofusion Welding
Site Preparation
Erecting the shelter, preparing the excavation, siting of equipment
Appropriate ambient temperature for welding and control of ambient temperature
Checks for generator, control box and tooling
Production of Electrofusion Welds (Straight Lengths)
Importance of site hygiene, Cleaning/preparation of pipe surface (conventional pipes)
Cleaning/preparation of pipe surface (pipes with protective skin)
Clamping, re-rounding of pipe and dealing with end reversion
Operation of the control box, Making the weld
Production of Electrofusion Welds (Coiled Pipes)
All of the elements for straight lengths plus the following
Understanding of difficulty and safety issues with coiled pipes
Specialist equipment (coil straighteners) for welding of coiled pipes
Techniques for welding of coiled pipes, Making the weld, Rejection of unsuitable welds
Assessment of Weld Quality
Alignment of weld and evidence of gaps, check for axial movement of pipe relative to fittings
Observation of melt indicators.
Maintenance
Maintenance of equipment, servicing and calibration of equipment
Records
Welding records, job supervision records and certification information for welding personnel
Training for Butt Fusion Welding
Introduction
Health and safety relevant to the welding process and working in the field
Relevant standards (WIS 4-32-08)
Differences between manual, semi automatic and automatic machines
Pressure rating and SDR rating for pipes and fittings
Correct storage for pipes and fittings
The consequences of producing a poor quality weld
The different types of PE (PE 80 and PE 100) and how these materials differ from Polypropylene and
Polyvinylchloride (PVC)
The effect of ovality and pipe end reversion
Techniques for destructive and non-destructive testing (NDT) of welds
Pupped bends and fittings (potential issues regarding clamping)
The commissioning pressure tests and pressure tests for electrofusion top tee and saddles
Importance of machine calibration and periodic checks on pipe surface preparation tools
Welding Equipment
Generator and use of power ratings relevant to the procedure being undertaken
Control box, machine chassis and clamps, hydraulic unit/control box, trimming tool and heater plate
Ancillary Equipment
Welding shelter, pipe support rollers, coil straightening equipment, techniques for lifting of pipes,
pipe cutters, PI tape, marker pen, Isopropanol cleaning wipes, digital thermometer and probe, timer,
bead measurement gauge, pipe end plugs, tools for de-beading the weld
Site Preparation
Preparing the excavation, erecting the shelter, siting of equipment, checking the equipment
use of ground sheets or baseboards
Appropriate ambient temperature for welding and control of ambient temperature
Training for Butt Fusion Welding
Preparation for welding
Cleaning the trimming tool, cleaning/washing the heater plate
Checking the pipe (for damage and excessive ovality)
Production of Butt Fusion Welds
1. Clamping
Positioning of the pipe, clamping of the pipes
2. Trimming
Using the trimming tool, Removing the pipe shavings from the machine
Checking the pipe ends (misalignment and mismatch)
3. Making the Weld
Dummy welds, Single pressure and dual pressure welding
Applying the heater plate, initial bead-up pressure and heater plate removal
Rejection of unsuitable welds
Assessment of Weld Quality
Removal and identification of internal and external weld beads and applying the twist test to weld beads
Maintenance
Maintenance of equipment and servicing and calibration of equipment
Records
Welding records, job supervision records, certification information for welding personnel
Calibration records, databases for recording welding production and location of welds
Theory Exam
• To ensure knowledge safe working/ production of high quality welds
• Separate exam for each qualification
• Exam will be 1 hour in duration with 20 multiple choice questions
• Failure to answer key questions will result in failure of whole exam
• Score of 80% required to proceed to the practical exam
Practical Test
• Carried out under site rather than classroom conditions
• Welding area set up in accordance with best safety and site practice
• Test to include welding of different pipe diameters
• Demonstrate ability to weld coils and handle long pipe lengths
• Welder and joints will be visually assessed
• Joints produced will be destructively tested
Welding Test Certificate
• Details of qualifications held on National database
• Welder provided with identity card containing qualification information
Retention of qualification provided:
• Welding undertaken with regular frequency (no inactivity>1 year)
• No issue regarding knowledge or practical ability of the welder
• Employer shall establish the competency of the welder on an annual
basis
Conclusions
• Draft specification well advanced. Publication hopefully in 2014
• Strong basis on practical competency under site conditions
• Theoretical exam will be more demanding that at present
• Practical test ensures competency in joining coiled pipe
• Welders must show competency in welding large diameters before
they are permitted to install these pipes on site
• Utilities can ensure competency of workforce by specifying the training
standard in their procurement documents
• Standard will improve quality of installation and reduce leakage