ASME B31.3 Process Piping: Valve Requirements and Procurement Guide

ASME B31.3 Process Piping is the most widely referenced piping code for refineries, chemical plants, pharmaceutical facilities, and industrial processing worldwide. When an EPC or owner specifies B31.3 compliance, they are invoking a comprehensive set of requirements that govern not only the design and fabrication of piping but also the materials and quality requirements for valves within that piping system. Understanding what B31.3 requires of valves — and what documentation must accompany compliant supply — is essential for procurement teams.

Scope of B31.3 for Valves

ASME B31.3 para. 300.1 states the code applies to all piping within the scope of process plants. Valves are pressure-containing components and are subject to all applicable requirements. The code classifies piping components (including valves) into listed and unlisted categories, and piping into normal fluid service and several special categories (Category D, Category M, High Pressure, High Purity). Most process plant valves fall under normal fluid service.

Listed vs Unlisted Valve Components

Listed Components

A listed valve is one manufactured to a standard explicitly listed in ASME B31.3 Table 326.1 — such as API 600, API 6D, ASME B16.34, API 602, API 603, MSS SP-42, or BS 5352. Listed valves are presumed to comply with B31.3 material and pressure-temperature requirements when used within the standard's rated conditions. The purchaser is not required to perform separate pressure calculations; the listed standard's tables govern.

Unlisted Components

A valve manufactured to a non-listed standard, or a special design not covered by any listed standard, is an unlisted component. For unlisted valves, the engineering designer must perform design calculations per B31.3 para. 304 to verify pressure-containing wall adequacy, and the valve must be pressure-tested per B31.3 para. 345. On large petrochemical projects, unlisted components require additional documentation review and owner/engineer approval — a significant procurement complication to avoid where possible.

Material Requirements

B31.3 para. 323 governs material requirements. Key points for valve procurement:

• Valve bodies must be made from materials listed in ASME B31.3 Table A-1 (metallic) or A-3 (bolting) — or qualified by the procedures in para. 323.1.2.
• Cast iron is permitted for normal fluid service below Class 125 flanged connections; it is prohibited for Category M fluids (highly toxic) and for temperatures below -29 degrees C or above 232 degrees C.
• Low-temperature service requires impact testing per B31.3 para. 323.2.2 — specify the minimum design temperature (MDT) at procurement; the valve manufacturer must provide impact test results.
• For high-temperature service (typically above 425 degrees C for carbon steel), alloy steel body materials (WC6, WC9, C12A) must be used; carbon steel loses strength progressively above this temperature.
• ASME B31.3 para. 323.3 prohibits use of certain materials in specific services — e.g., copper alloys in ammonia service, unlined cast iron in Category M service.

Examination Requirements

B31.3 para. 341 specifies examination requirements. For valves as standard components, the primary obligation is on the manufacturer to perform examinations per the listed standard (e.g., API 600 requires wall thickness dimensional inspection, hydrostatic shell test, and API 598 seat test). The owner or EPC may impose additional examinations through the purchase specification:

• Radiographic testing (RT) of body castings — typically required for Class 600 and above, or for Category M service.
• Ultrasonic testing (UT) of forgings — required for high-alloy or heavy-wall valves.
• Positive Material Identification (PMI) — increasingly standard on all alloy steel (WC9, P91, SS 316L, duplex) valves; verifies heat chemistry matches the MTC.
• Hardness testing — required for NACE MR0175/ISO 15156 compliance (sour service); also used to verify PWHT effectiveness.
• Magnetic particle testing (MT) or liquid penetrant testing (PT) — for weld repairs and non-magnetic materials respectively.

Pressure Testing per B31.3

B31.3 para. 345 requires pressure testing of installed piping systems. For individual valves, the pressure test is typically performed by the valve manufacturer per the relevant valve standard (API 598 for most valve types). The manufacturer's certificate of hydrotest is a required document in the B31.3 valve documentation package. The installed system hydro test is a separate requirement performed by the contractor after erection.

Required Documentation Package

A complete B31.3-compliant valve documentation package typically includes:

• Material Test Certificates (MTCs) to EN 10204 3.1 for pressure-containing parts (body, bonnet, trim) — showing chemical analysis and mechanical properties.
• EN 10204 3.2 (third-party witness) for Category M or Class 900+ applications.
• Hydrostatic shell test certificate — per API 598 or equivalent.
• Seat leakage test certificate — per API 598 (Rate A, B, or D as specified).
• Dimensional inspection report — confirming face-to-face, flange dimensions per applicable standard.
• NDE reports (RT, UT, MT, PT) as required by specification.
• PMI report — for all alloy steel and stainless steel valves.
• PWHT records — for alloy steel valves where body welding or repair welding has been done.
• API monogram certificate (if API monogram is specified on the PO).
• Material identification/traceability marking on the valve — typically stamped or nameplate; must match MTC heat number.

Special Fluid Service Categories

Category M (highly toxic, immediately dangerous to life) and High Purity services impose additional valve requirements: 100% RT of body casting, 3.2 material certificates, zero permissible leakage on seat test, and additional examination hold points. For Category M, valves with cast iron bodies are prohibited entirely. For High Purity (semiconductor, pharmaceutical) service, all internal surfaces must meet surface finish and cleanliness requirements specified by the owner — electropolishing to Ra 0.25 micron is typical for pharmaceutical water-for-injection (WFI) systems.