What Documentation Is Required for Steel Flanges in ASME B31.3 Piping Systems?

When a process piping system is designed to ASME B31.3, every flange bolted into the line has to be traceable back to a specification. The paperwork behind a flange is not an afterthought: it is how the engineer, the inspector and the owner confirm that the component is the right material, made to the right dimensions and capable of the pressure and temperature the design demands. Knowing what documentation is required for steel flanges in ASME B31.3 piping systems saves you from accepting a batch that later fails a hydrotest or a material audit.

This article breaks down the documents you should expect for steel flanges under B31.3, separates what the code itself demands from what owners and project specifications usually add, and gives you a practical checklist to run before flanges leave the supplier or enter the laydown yard.

1. What ASME B31.3 Actually Requires

A common misconception is that B31.3 demands a thick folder of certificates for every flange. In fact, the code's minimum requirement is comparatively lean. Under B31.3, pressure-retaining components such as flanges must be identified so that the material specification, grade and heat or lot can be traced, and the component must carry the markings required by its governing standard. For a steel flange made to ASME B16.5, that means permanent identification showing the manufacturer, the material grade and the pressure class.

The code does not, as a minimum, require a Certificate of Conformance or an independent certification body stamp on every flange. What it does require is that the flange be identifiable and that its material be verified against the design specification. The gap between this code minimum and what actually arrives on site is usually filled by the owner's project specification, which is where most of the documentation you will handle comes from.

2. The Material Test Report: The Backbone of Traceability

The single most important document for a steel flange is the Material Test Report (MTR), also called a mill test certificate or certified material test report (CMTR). It is issued by the material producer and states the chemical composition and mechanical properties of the heat from which the flange was forged. For a flange, the MTR should tie back to the forging lot, and the heat number on the certificate must match the heat number stamped on the flange itself.

When you review an MTR for a flange, check three things in particular:

Chemical composition – every element listed must fall within the limits of the governing material specification, for example ASTM A105 for carbon steel or ASTM A182 for alloy and stainless grades.
Mechanical properties – tensile strength, yield strength and elongation should meet the specification's minimum values, and hardness should sit within the permitted range.
Heat treatment – the report should record the heat treatment condition, such as normalised for A105N, because it directly affects the flange's mechanical performance.

3. Flange-Specific Checks Beyond the Mill Certificate

A mill certificate proves the raw material, but it does not prove the finished flange. That is why project specifications typically add documents that verify the flange as a manufactured component:

Dimensional inspection report – records the flange outside diameter, bolt circle, bolt hole size and count, raised face diameter, thickness and bore against ASME B16.5 or the applicable standard. This is a direct measurement check, not a certificate of intent.
Positive Material Identification (PMI) – a non-destructive test, usually by X-ray fluorescence, that confirms the alloy composition of the finished flange. It is commonly required for alloy and stainless flanges where a mix-up would be hard to spot by eye.
Hardness test report – often required for carbon steel flanges in sour service, where the specification limits hardness to control cracking risk.
Pressure test certificate – where the project requires it, confirming the flange or flange assembly has been hydrostatically tested and held pressure without leakage.

4. Code Minimums vs. Owner and Project Specifications

The distinction between what the code requires and what the owner requires is worth spelling out, because it decides how much documentation you must collect. B31.3 sets the floor: identifiable components, verified material, and markings per the governing standard. Owners and EPC contractors then raise the bar in their project specifications. It is common to see requirements for full CMTRs on every flange, 100% PMI on alloy and stainless flanges, third-party inspection with a release note, and retention of records for the life of the plant or a defined period after handover.

If you are the buyer, read the project specification before you order and list every document it names. If you are the supplier, quote the documentation package up front so there are no surprises at inspection. Either way, the documents you need for steel flanges in a B31.3 system are defined more by the project spec than by the code itself.

5. A Receiving Inspection Checklist for Steel Flanges

Documentation only earns its keep when it is checked against the physical component. Before you accept a delivery of steel flanges, run through this list:

Markings match the paperwork – the heat number, grade and class stamped on each flange should match the MTR and the purchase order.
Dimensions are measured, not assumed – spot-check the bolt circle, bolt holes and facing against the standard.
PMI results are recorded – for alloy and stainless flanges, confirm the report is traceable by heat number.
Special requirements are covered – if the line is in sour service or low temperature, confirm the hardness and impact test documents are present.
Non-conformances are quarantined – anything that does not match should be set aside and flagged to the supplier, not mixed into the laydown.

6. Getting Steel Flanges with the Right Paperwork

Because documentation is only as good as the production behind it, the supplier you choose matters as much as the checklist you run. A manufacturer with controlled forging, heat treatment and inspection should be able to supply steel flanges with full material test reports, dimensional verification and, where required, PMI and pressure test certificates.

EZ Steel Industrial supplies pipe flanges and related piping components for oil and gas, petrochemical and industrial projects. Its production covers carbon, alloy and stainless steel flange materials, and its quality system includes hydrostatic testing, ultrasonic inspection and mill test certificates. Rather than accepting a certificate at face value, you can review its inspection records and project supply documentation to confirm that what is delivered matches what you specified for your B31.3 system.

Before you approve any steel flange for an ASME B31.3 line, ask how the material was verified, request the MTR and any PMI or dimensional reports, and confirm the heat numbers line up. A few minutes of document review at the point of supply is far cheaper than pulling a flange out of a tested line because the paperwork could not be matched to the metal.