ASME B31.1 vs B31.3 Piping: Which Code Governs Your Valve Installation

The Short Answer

ASME B31.1 and B31.3 are two different power and process piping codes published by ASME, and the valve installation question comes down to which code the plant is designed under. B31.1 covers power piping, typically in utility and industrial boiler plants, while B31.3 covers process piping, typically in refineries, chemical plants, and similar process facilities. The two codes differ in design basis, material selection logic, pressure-temperature rating philosophy, and inspection expectations, and a valve that is acceptable under one code may not carry the documentation required under the other. The practical rule for a buyer is to identify the governing code for the plant before ordering, because the valve pressure class, material certification, and test documentation all follow from that decision.

What B31.1 and B31.3 Each Cover

B31.1, the Power Piping Code, applies to piping in electric generating stations, industrial and institutional plants, and central and district heating systems, including boiler external piping. Its focus is reliability under sustained high-temperature and high-pressure steam service, where a failure has large consequences. B31.3, the Process Piping Code, applies to piping in chemical and petroleum plants and other process facilities, and it is more flexible in design because process plants run a wide range of media, temperatures, and pressures. The two codes are separate by design, and a piping system is typically built to one code or the other, not both, although a single facility may have areas governed by each.

How the Codes Treat Valves

Aspect	B31.1 Power Piping	B31.3 Process Piping
Typical service	Steam, high temperature water, boiler systems	Process fluids, chemicals, hydrocarbons
Design philosophy	Conservative, sustained-load oriented	Service-condition driven, flexible
Material documentation	Strict traceability expectations	Service-class dependent
Valve relevance	Pressure class and material verification matter	Material compatibility often decides

The table captures typical orientation; the detailed requirements differ by chapter and by the specific service conditions, and the current edition of each code should be checked for the exact rules.

Why the Distinction Matters for Valve Selection

The code tells the valve specifier what the valve needs to prove. In a B31.1 power piping installation, the dominant questions are pressure-temperature rating, material traceability, and documentation, because the steam service rewards conservative, verifiable choices. In a B31.3 process line, the dominant questions shift to material compatibility with the media, sealing performance, and the pressure-temperature class for the specific fluid, because a corrosive or toxic process fluid changes the risk profile entirely. The same nominal valve class can be a correct choice in one plant and the wrong one in the other, not because the valve differs, but because the acceptance criteria differ. Buyers who carry a valve from a process plant into a power plant, or the reverse, without rechecking the code requirements are the ones who get caught at inspection.

Documentation and Certification

The practical burden of the code shows up in the paperwork. Power piping installations generally expect material test reports and traceability for pressure-containing components, and the valve body and bonnet material records need to line up with the requirements. Process piping installations ask similar questions but the depth depends on the fluid service class, and a low-hazard service may need far less documentation than a high-pressure toxic service. The broader logic of how standards interact for valves is covered in the ANSI versus API valve standards guide, and for pipeline service specifically the API 6D pipeline valve standard explains where that product standard fits relative to the piping codes. When the valve documentation does not match the governing code, the safest move is to confirm the requirement with the plant’s piping engineer before the valve reaches the site.

Where to Start on a New Project

On a new project the code decision is usually made by the piping and process engineers early in the design, and the valve list simply inherits it. On a replacement or expansion project, the existing plant code is the starting point, and changing the governing code is a design decision, not a procurement shortcut. Either way, the valve specification should state the governing code and edition explicitly, because the manufacturer uses that statement to decide which documentation to provide. A specification that says only “per ASME” leaves the material certification and test evidence open to interpretation, and the inspection stage is the wrong place to discover the mismatch.

Code Edition and Plant Boundaries

Two practical traps deserve attention. The first is the code edition: ASME publishes revised editions of B31.1 and B31.3, and the requirements in force depend on the edition the plant was designed to and any jurisdictional adoptions in the region. A valve documentation package that satisfied an older edition may not cover what a newer edition asks for, and the project should name the edition in the specification. The second trap is the boundary inside a single facility. A refinery, for example, typically runs its process units under B31.3, but a powerhouse or boiler area within the same site may be under B31.1, so the same plant can legitimately use both codes in different areas. The valve specifier needs to know which area the valve serves, because the paperwork and acceptance criteria travel with the code, not with the site name.

Engineering Judgment

For a buyer or specifier, the decision sequence is short. Identify the governing piping code, confirm the pressure class and material expectations under that code, and then verify the valve’s documentation against those expectations before ordering. The mistake is to treat B31.1 and B31.3 as interchangeable labels when they are separate design frameworks with different inspection cultures. Where the plant engineer is unsure which code applies, the boundary usually falls along the process versus power line, and the plant’s design basis document settles it. The code edition matters as well, because requirements are revised, and the project should record the code edition that governs so the documentation matches the standard that was actually in force.

Sources & Further Reading: ASME

This article provides general educational knowledge only and is not professional engineering advice.

Tags: Valve Standards