61
Coverage of non-metals in the ASME B31.3 Chemical
Plant and Petroleum Refinery Piping Code
W E Short 11, MS(Eng), BS(MechEng),PEng
ICI Americas Inc., ICI Engineering North America, Wilmington, Delaware, USA
The chemical and petrochemical industries have decades of experience in specifying metallic piping lined with non-metals as a cost
effective alternative to high-priced alloy materials of construction for piping in corrosive service. Early on, application of plastic piping
was essentially limited to atmospheric chemical sewage service and to above-ground vents and drains. However, applications and usage
of plastic piping continue to increase as engineers become more confident in specifying plastic materials and mechanical contractors
gain experience with their installation. Nun-metallic materials are being developed that are not only corrosion resistant but also have
increasingly higher pressure and temperature capabilities. Plastic double-containment piping has experienced tremendous growth for
handling hazards and toxic ,fluids. In the United States, recent dramatic growth of plastic double-containment piping applications has
been, to a large extent, for compliance with the Environmental Protection Agency (EPA) regulations of the 1976 Resource Conservation and Recovery Act (RCRA). Related E P A regulatory efforts were accelerated in I988 by more stringent amendments to this
legislation. industry in the United States must comply with these E P A regulations by December I998.
Plastic piping and metallic piping lined with non-metals have been covered to some extent by the A S M E B31.3 Chemical Plant and
Petroleum Refinery Piping Code for several years. The distinctive requirements of nonmetallic piping and piping lined with non-metals
were incorporated into the 1980 edition as a separate Chapter VZZ,which is dedicated to this growing area of interest in piping.
This paper provides an overview of the present coverage of non-metallic piping lined with non-metals in the A S M E 831.3 Chemical
Plant and Petroleum Refinery Piping Code (1).Some topics that warrant further investigation are presented as well.
1 INTRODUCTION
Non-metallic piping and metallic piping lined with nonmetals have been used for years as a cost effective
alternative to high-priced alloy piping in applications
where high corrosion rates are experienced or rigid
cleanliness standards are required.
Not too surprisingly, the first water supply piping
was made of wood, a non-metallic material. Holes were
bored through wood logs and the joints were nipples
made of wood or metal (2).
Plastic polyethylene piping has been widely used for
gas distribution where a high mechanical integrity
piping system is required. In the United Kingdom, 80
per cent of the low-pressure natural gas mains and more
than 95 per cent of local gas service piping installed
annually is polyethylene. Polyethylene has been used for
gas distribution piping in Scandinavia and West
Germany as well. Presently, about 18 per cent of the
natural gas distribution piping in the United States is
plastic, predominantly polyethylene (3). Other sources
have advised that about 85 per cent of new natural gas
mains and 95 per cent of new natural gas service lines
installed throughout the United States are polyethylene
piping. This trend towards the use of plastics appears to
be steadily increasing for a variety of other industrial
and chemical plant piping applications as well (3).
In the late 1970s, the semiconductor industry experienced occasional leaks in underground transfer piping
used to handle highly corrosive process wastes, as well
as toxic fluids. Such leaks eventually lead to problems
with groundwater contamination. Double-containment
piping systems constructed of various plastic materials
were installed to address this problem. Materials of construction consisted of combinations of FRP, PVC, polyethylene, polypropylene and PVDF. Today in the
United States, plastic double-containment piping
systems are commonly used in response to growing government legislation and regulations aimed at protecting
the environment and to satisfy increasingly more stringent insurance requirements (4).
There is considerable experience in the speciality
chemical industry with metallic piping lined with
thermoplastics, such as carbon steel piping lined with
PTFE, PVDF or PVC (Table 1). Borosilicate glass
piping has been used to handle corrosive fluids at relatively low pressures. Reinforced thermosetting resin
(that is FRP) piping has been used successfully in a
variety of corrosive service applications. In recent years,
more widespread use of plastic piping has been experienced for industrial applications (2).
Essentially all plastic materials can be produced in
the form of pipe. Commercially available plastic pipe
materials have been limited by practical manufacturing
considerations as well as by the properties of the
various plastic materials (2).
Plastics are high polymers that can be separated into
two distinct groups, namely thermoplastic materials and
thermosetting materials (2, 5). In general, non-metallic
Table 1 Some common thermoplastic materials
used for piping or linings in piping
Abbreviation
Term
ABS
CAB
CPVC
FEP
PB
PE
PFA
PP
PTFE
PVC
PVDC
PVDF
Acrylonitrile-butadiene-styrene
Cellulose acetate-butyrate
Chlorinated polyvinyl chloride
Perfluor0 ethylene-propylene
Polybutylene
Polyethylene
Poly peduoroalkoxy alkane
Polypropylene
Polytetrafluoroethylene
Polyvinyl chloride
Polyvinylidene chloride
Polyvinylidene fluoride
The M S was receiwd on 2 October 1990 and wus ucrepted for publication on 13
September 1991.
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piping and metal piping lined with non-metals can be
classified into one of the following categories:
1.
2.
3.
4.
Thermoplastics
Reinforced thermosetting resins
Miscellaneous non-metals
Non-metallic lined metal
Thermoplastic piping is made of plastic materials that
can be repeatedly softened by heating and then hardened by cooling. In the softened state, thermoplastics
can be fused or shaped by flow. Thermoplastic materials
are available in a great number of different types (2, 5).
The approximate temperature limits for some thermoplastics used as linings are listed in Table 2 (6, Table
A323.4.3).
Thermosetting plastics are composite structures, composed of multi-component laminents or blends of
polymer and particulate or fibrous fillers. Thermosetting plastics cannot be fused without experiencing
thermal or mechanical degradation. Thermosetting
materials are available in only a few types, and the
material in itself lacks strength (2, 5). The approximate
temperature limits for some thermosetting resin pipe are
listed in Table 3 (6, Table A323.4.2C). Reinforced
thermosetting resin (RTR) pipe is made of cured epoxy
or polyester resins reinforced with glass fibre or other
fibres. Reinforced plastic mortor (RPM) pipe consists of
fibrous reinforcement and aggregate embedded in or
surrounded by cured thermosetting resin (7, 8). RTR
and RPM piping are produced by centrifugal casting,
hand lay-up (that is contact moulding) or filament
winding (2,5,8).
Miscellaneous non-metallic piping includes piping
manufactured of materials such as reinforced concrete,
vitrified clay and borosilicate glass.
The more widespread usage of plastics demands
closer attention to safety in the design of such piping
systems. Safe design rules and guidelines are set forth in
the ASME B31.3 Piping Code (6). As the Code is
adapted into legislation, the importance for piping engineers to ensure compliance with its requirements
grows accordingly.
Table 2 Approximate temperature limits for some thermoplastics used as linings (6)
Minimum temperature
Materials
"F
"C
PFA
FEP
PP
PTFE
PVDC
PVDF
- 325
325
0
- 325
0
0
~
Maximum temperature
"F
"C
- 198
500
- 198
- 198
400
225
500
- 18
18
175
275
260
204
I07
260
79
135
-18
~
Table 3 Approximate temperature limits
thermosetting resin pipe (6)
Materials
for
some
Minimum
temperature
Maximum
temperature
Resin
Reinforcine
"F
"C
"F
"C
Polyester
Furan
Glass fibre
Carbon
Glass fibre
-20
-20
-20
-29
-29
-29
200
200
200
93
93
93
Furan
The 1980 edition of the ANSI/ASME B31.3 Chemical
Plant and Petroleum Refinery Piping Code Section was
reorganized to place the requirements for non-metals
into a separate Chapter VII, titled 'Nonmetallic piping
and piping lined with nonmetals'. This subject had been
generally covered in the previous editions of the Code
(6) since 1976, but the requirements for non-metals were
scattered throughout the various chapters.
Organization of Chapter VII in the Code parallels
that of the first six chapters, which is referred to as the
Base Code. Corresponding text in the Base Code and
Chapter VII have the same paragraph designations,
except that each paragraph in Chapter VII begins with
the prefix 'A.
In the following paragraphs of this paper, the use of
the term Code refers to the ASME B31.3 Piping Code
(6). The applicable paragraph in Chapter VII of the
Code is referenced in brackets.
2 CHAPTER VII APPLIED TO METALLIC PIPING
LINED WITH NON-METALS
For metallic piping lined with non-metals, the metal
piping provides the structural strength required for
pressure containment. As such, the Code provides that
the outer metallic piping portion must be designed to
comply with the Base Code requirements. Typically, the
liner is considered primarily for corrosion resistance,
and no credit is given to the liner for withstanding pressure. However, the Code provides that the properties of
both the outer metallic and the lining materials, as well
as the bond between them, must be considered in establishing the design temperature. Also, consideration must
be given to the liner for external pressure or vacuum
design (6, A323.4.3).
Allowances for pressure and temperature variations
on metallic pipe lined with non-metals are permitted if
the lining material is suitable for the increased conditions (6, A302.2.4).
In addition to the general requirements for welding
set forth in the Base Code, Chapter VII specifies some
welding requirements intended to maintain the integrity
of the lining (6, A329).
The Code does not specifically limit the fluid services
for metallic piping lined with non-metals. The fluid
service limitations for non-metals in Chapter VII do not
apply to the materials used as linings. However, the
outer metal material must comply with the Base Code
(6, A323.4.3).
3 CHAPTER VII APPLIED TO NON-METALLIC
PIPING
Chapter VII requires that the following points be considered in the selection of materials, design and manufacturing of non-metallic piping systems (6, A302.1):
1. Tensile, compression, flexural and shear strength,
and elastic modulus at design temperature
2. Creep rate at design conditions
3. Design stress and basis of design stress
4. Ductility and plasticity
5. Impact and thermal shock properties
6. Temperature limits
7. Transition temperature of melting and vaporization
8. Porosity and permeability
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COVERAGE OF NON-METALS IN THE ASME 8 3 1 3 CP AND PR PIPING CODE
9. Testing methods
10. Methods of making joints, and the joint efficiency
11. Possibility of deterioration in service
Listed components are piping components based
upon standards or specifications that are referenced in
the Code. Table A326.1 in Chapter VII of the Code lists
component standards for non-metallic piping. Listed
non-metallic components that do not have specific
pressure-temperature ratings must be rated by the Code
pressure design rules. Design stresses have not been
developed for some non-metallic components that do
not have pressure-temperature ratings. The Code
requires that such unlisted piping components must be
qualified by extensive successful service experience or
performance tests (6, A302.2, A304.7).
Unlike the Code requirements for metallic piping,
allowances for pressure and/or temperature variations
above the design conditions are not permitted for nonmetallic piping. The design conditions are established
by the most severe coincident pressure and temperature
conditions (6,A302.2.4).
The Code lists allowable stresses for various nonmetals. For thermoplastics, the hydrostatic design stress
(HDS) is provided for various materials (6, Table B-1).
The HDS is the maximum continuous stress due to
internal pressure used in the design of plastic piping.
The HDS is determined from selected properties of
plastic piping materials, referred to as the hydrostatic
design basis (HDB) by use of a design service factor.
The basis for determining the HDS is described in
ASTM D2837 (9).
The design stress (DS) for the laminated reinforced
thermosetting resin materials listed in the Code (6,
Table B-2) are established at one-tenth times the
minimum tensile strengths presented in ASTM C582 (9)
and are limited to design temperatures within the range
- 29-82°C (- 20-180°F).
For the filament-wound RTR and centrifugally cast
RPM materials listed in the Code (6, Table B-3), the
hydrostatic design basis stress (HDBS) is established by
the procedures set forth in ASTM D2992 (9), but is
limited to a design temperature of 23°C (73°F). Typically, the recommended temperature limits for RTR and
RPM are much higher, 93-149°C (200-300°F) (6, Table
A323.4.2C). The designer should consult with the manufacturer for specific applications, particularly as the
temperature limitations are approached. The initial
set-up costs and associated time to satisfy the ASTM
D2992 procedures can be somewhat expensive. HDBS
is determined by the piping manufacturer.
The HDS is obtained by the following equation:
HDS
where
=
F (HDBS)
F = design service factor from ASTM D2992 (9)
F < 0.5 for the static HDBS and F < 1 for the cyclic
HDBS (6, A302.3.2).
At present, the Code does not provide design rules for
external pressure of non-metallic piping. Stresses from
uniform external pressure of the components are qualified by extensive service experience or performance
tests.
External loading stresses are based on ASTM D2321
(9) or AWWA C900 (9) for thermoplastic piping and
69
ASTM D3839 (9) or AWWA C950 (7) for RTR and
RPM piping. Also for non-metallic piping, diametric
deflection from external loading is limited to 5 per cent
of the pipe inside diameter (6, A302.3.3). Occasional
loads are considered to act concurrently with any external loading. Test conditions are not subject to these
stress limits (6, A302.3.4).
4 PRESSURE DESIGN RULES FOR NON-METALLIC
PIPING
For non-metallic straight pipe under internal pressure,
the design thickness is determined by the following
equations, using the appropriate Code stress values (6,
A304.1):
For thermoplastic pipe:
PD
2s + P
t=-
For RTR pipe (laminated) :
t=-
PD
2s P
+
For RTR and RPM pipe (filament wound and centrifugal cast):
t=
PD
2SF + P
where
t = pressure design thickness (inches)
F = design service factor (dimensionless)
P = internal design pressure (lb/in2 gauge)
D = pipe outside diameter (inches)
S = design stress (lb/in2)
The minimum required thickness of non-metallic
straight pipe is determined by the following equation:
t,=t+c
where
t,
t
c
= minimum required thickness (inches)
= pressure design thickness (inches)
= sum of mechanical allowances plus
corrosion
and erosion allowances
Where excess wall thickness is not available in the pipe
for an intersecting branch connection, the amount of
additional reinforcement must be qualified.
The Code allows plastic flanges for use with flat ring
gaskets to be designed in accordance with Appendix 2
of the ASME BPV Code Section VIII, Division 1 (lo),
but the allowable stresses and temperature limits of
Chapter VII apply. For plastic flanges using full face
gaskets, the design rules of Appendix Y of the ASME
BPV Code (10) apply.
5 FLEXIBILITY OF NON-METALLIC PIPING
While some general guidance is provided to assure adequate flexibility, the Code does not provide any specific
stress-limiting criteria nor methods for stress analysis of
non-metallic piping systems. This is because of the significant difference of the stress-strain behaviour of nonmetals in comparison to metals. In particular, Poisson’s
ratio varies greatly for the various plastic materials and
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2. Name of the employer who qualified the bonder or
bonding operator
3. Date of the qualification
4. Date the bonder or bonding operator last bonded
pressure piping under the performance qualification
Bonders or bonding operators must be separately qualified for any different BPS. The bonding qualification
requirements per the Code apply to the circumferential
joints.
To comply with the Code, joints for plastic piping are
permitted to be made only in accordance with a qualified written BPS. The bonders or bonding operators
who are performing the bonding must have passed a
performance qualification test that was performed in
accordance with a qualified BPS. Each pressurecontaining bond is stenciled nearby with the identification symbol of the bonder or bonding operator. While
the employer of the bonder or bonding operator is
responsible for ensuring the quality of the production
joints, it is the owner’s responsibility to require that
such joints must comply with the requirements in
Chapter VII of the Code.
Some specific requirements for preparation and procedure of the following joints are covered in Chapter
VII :
temperatures, and the simplified formulae used as the
Code design basis for stress analysis of metallic piping
may not be valid for some non-metals (6, A319).
Thc Code requires that substantial flexibility must be
provided by the piping system layout to ensure that displacement stresses are minimized (6, A3 19). While this
approach should allow for a high degree of safety, it is
not always cost effective for industry (4).
6 BONDING REQUIREMENTS
Chapter VTI of the Code requires that a written
bonding procedure specification (BPS) must be prepared for bonding joints of thermoplastic, RTR and
RPM piping. The BPS must be qualified, and the performance of bonders and bonding operators must be
qualified to that BPS (6, A328). The BPS must specify:
1. Procedure for making the bonds
2. Tools and fixtures required
3. Care and handling of tools and fixtures
4. Temperature, humidity and calibration requirements
5. Joint preparation
6. Dimensional requirements and tolerances
7. Cure time
8. Protection of work
9. Tcsts and examinations required
10. Acceptance criteria for the completed test assembly
Typical solvent cemented and heat fusion joints in
thermoplastic piping are shown in Fig. 1, while typical
adhesive and butt-and-wrapped joints in thermosetting
piping are shown in Fig. 2.
Acceptance criteria for bonded joints are summarized
in Table 4 (6, Table A341.3.2). The completed non-
Qualification of the BPS and of the bonders and
bonding operators is documented by a performance
qualification record (PQR) which verifies:
1. Name of the bonder or bonding operator and the
BPS that was qualified
Socket joint
Solvent cemented joint
R T R and R P M piping
Adhesive joints
Butt-and-wrapped joints
Thermoplastic piping
Hot gas welded joints
Solvent cemented joints
Heat fusion joints
Socket joint
Butt joint
Heat fusion joints
Fig. 1 Typical thermoplastic piping joints (6)
Table 4 Acceptance criteria for bonded ioints (6)
Thermoplastic
Imperfection
Hot gas
welded
Solvent
cemented
Heat
fusion
RTR and RPM
Adhesive
cemented
Crack 9
Unfilled areas in joint
Unbonded areas in joint
Inclusions of charred material
Unfused filler material inclusions
Protrusion of material into pipe bore, % of pipe wall
thickness
None permitted
None permitted
Not applicable
None permitted
None permitted
Not applicable
Not applicable
None permitted
None permitted
Not applicable
Not applicable
Cement, 50%
Not applicable
None permitted
None permitted
Not applicable
Not applicable
Fused material, 25%
Not applicable
None permitted
None permitted
Not applicable
Not applicable
Adhesive, 25%
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COVERAGE OF NON-METALS IN THE ASME B31.3 CP A N D PR PIPING CODE
Overwrapped
bell-and-spigot joint
Butt-and-wrapped joint
71
Fully tapered joint
Fig. 2 Typical thermosetting piping joints
metallic piping system must be leak pressure tested to
ensure tightness. The hydrostatic test should be to a
minimum 1.5 times the design pressure, but not greater
than 1.5 times the maximum rated pressure of the
lowest rated component (6, A345).
7 SPECIAL LIMITATIONS
The use of plastic piping in Category M service is
limited to RTR piping, which also must be safeguarded
when used in toxic or flammable service (6, MA323.4.2,
A323.4.2).
Thermoplastic and RPM piping must be safeguarded
when used in other than Category D service. The Code
prohibits the use of thermoplastic piping in aboveground flammable service (6, A323.4.2).
Borosilicate glass piping must be safeguarded for
toxic or flammable services and for large, rapid temperature changes (6, A323.4.2).
The jurisdiction of local statutes and building regulations must be observed for all Code piping categories.
8 PRECAUTIONARY CONSIDERATIONS
The Code identifies some special considerations when
using non-metallic piping. For thermoplastics, safeguarding should be considered for above-ground compressed gas service. The lack of ductility and its poor
resistance to thermal and mechanical shock should be
taken into account for borosilicate glass piping.
Methods to minimize the buildup of potentially dangerous electrostatic charges should be considered in the
design of non-metallic piping systems that handle electrically non-conductive fluids (6, FA323.4).
9 FUTURE CODE CONSIDERATIONS FOR
NON-METALLIC PIPING
In many areas of non-metallic piping, Code progress is
at a standstill. To a large extent, this is due to lack of
standardization for plastic piping components. Insufficient information about the properties of various plastic
materials is also a contributing factor.
Some areas of research that could lead to improved
coverage of non-metallic piping in Chapter VII of the
Code include :
1. Development of HDS for thermoplastic piping
materials above 38°C (100°F)
2. Development of HDBS for RTR piping materials
above 23°C (73°F)
3. Standardization of dimensions for non-metallic
flanges
4. Establish pressuretemperature ratings for nonmetallic flanges and flanges on metallic piping lined
with non-metals, considering:
(a) flange type
(b) flange face configuration
(c) pipe size
(d) bolting torque, sequence and lubrication
(e) gasket selection
5. Develop external pressure limits and procedures for
plastic piping
6 . Investigate the reaction of non-metals to cyclic and
non-cyclic thermal stress and develop stress intensification factors for non-metallic pipe and fittings
Also, the Code should incorporate coverage for plastic
double-containment piping systems. With expanded
safeguarding, non-metallic piping should be considered
for possible increased acceptability in Category ‘M’
fluid service.
The ASME has provided some funding for the Pressure Vessel Research Council (PVRC) of the Welding
Research Council (WRC) to address concerns of the
ASME B31 Section Piping Code regarding
advancement and improved coverage of non-metals.
The PVRC task group on polymers for pressure components has been established to investigate the various
concerns about non-metallic piping. Several activities
have been initiated for plastic piping, including testing
of thermoplastic pipe at various temperatures, development of a test plan to assess external pressure limits,
review of international plastic standards and a literature
search (11).
In order to carry out all the research and engineering
to make the necessary advancements in the area of non-
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metallic piping, financial support of the research programmcs and continued sponsorship of qualified
engineers to participate will be required from industry
as well.
5
6
ACKNOWLEDGEMENTS
This paper is an updated version of a previous paper,
based on the 1987 edition of the ASME B31.3 CP&PR
Piping Code and prepared as an ASME publication in
1989 (12). Significant changes in the coverage for nonmetals in the 1990 edition of the ASME B31.3 CP&PR
Piping Code are incorporated. Also, additional current
references have been included as appropriate.
I
8
9
10
REFERENCES
1 ASME B31.3 chemical plant and petroleum re3nery piping, 1990
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Mechanical Engineers, New York).
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3 Watson, M. N. Welding plastics pipes. The Welding Institute Bulletin, Cambridge, March-April 1988.
4 Ziu, C. G. Flexibility and stress analysis of thermoplastic doublecontainment piping systems. Codes and standards and applications
JOT design and analysis of pressure vessel and piping components-
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1989, ASME PVP-Vol. 161, July 1989, pp. 91-98 (American
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Mallison, J. H. Chemical plant design with reinforced plastics, 1969,
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(American Society of Mechanical Engineers, New York).
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York).
Leon, G. F. Design of plastic piping and fittings-A PVRC
program. Advances in bolted joint technology-1989, ASME PVPVol. 158, July 1989, pp. 81-86 (American Society of Mechanical
Engineers, New York).
Short 11, W. E. Overview of Chapter VII, ‘Nonmetallic piping and
piping lined with nonmetals’, in the ASME 831.3 CP&PR piping
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Part E:Journal of Process Mechanical Engineering
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