Upgrading the ASME B31.3 Pipe Code to Deal with FRP Pipe

FRP (Fiberglass Reinforced Plastic) pipe, as with other materials, is required to comply with the ASME B31.3 Pressure Process Piping Code. There are deficiencies in the Code relative to FRP. FRP is a unique material in that there are no established pressure-temperature ratings as there are for other materials, e.g. steel, PVC. The Code does provide rules for pressure design of components with no established ratings. However, the rules for FRP can be very confusing and ambiguous. The code provides rules for stress analysis of pipe systems but does not adequately address the unique properties of FRP. The installation and testing requirements for FRP also need to be updated. This paper will summarize the ASME Pressure Piping Code current requirements for the pressure design, stress analysis, and installation of FRP pipe in process applications (excluding gas pressure pipe and non-pressure applications). A Pipe Project Team is currently working under Task Group F of ASME B31.3 to review and revise the Code as it deals with FRP and the paper will also provide an update on the status of that review and recommended changes.

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INTRODUCTION

ASME B31.3, Process Piping, contains mandatory rules for non metallic piping in Chapter VII (ASME B31.1, Power Piping, contains non-mandatory rules in Appendix III and is virtually identical to B31.3 in dealing with FRP pipe. The Code does not properly address allowable stresses for loads other than pressure. Safe and accurate design and analysis of FRP pipe systems requires a more rigorous approach than currently out lined in the code. This paper will clarify the current code requirements, identify potential deficiencies, and provide current recommendations for upgrading the B31.3 based on the work of the ASME project Team.

CURRENT CODE REQUIREMENTS

Pressure/temperature ratings

The Code allows the use of three different pressure-temperature design criteria for pipe and fittings:

1) Listed Components having established pressure-temperature ratings can be used. (Listed Components refers to components for which a standard or specification is listed in Table A326.1 of the Code. The pressure -temperature rating must be included in the standard or specification).

2) Listed Components for which design stresses have been established in accordance with the Code can be used. The Code provides a method for calculating design stress based on ultimate stresses, which have been established in accordance with standards, or specifications listed in Table A326.1 of the code. A pressure design method for calculating minimum pipe wall thickness based on the design stress is included.

3) Unlisted Components can be used if their pressure design satisfies one of the following:

a) They conform to a published specification or standard; and the designer is satisfied they are similar in composition, mechanical properties, and method of manufacture to listed components; and their pressure design satisfies the formulas for pressure design in the code.

b) The pressure design is based on calculation and verified by extensive successful experience under comparable conditions with similarly proportioned components of the same or like material.

c) The pressure design is based on calculation and verified by performance test, which takes into consideration design conditions, dynamic and creep effects, and verifies the suitability of the component for its design life.

Table A 326.1 Component Standards includes ASTM (American Society of Testing Materials), API (American Petroleum Institute), and AWWA (American Water Works Association) standards for FRP, Glass, Thermoplastic, Thermoplastic Lined Steel, and other non-metallic pipe, fittings, an