company news about Flange Inspection and Documentation: PMI, Hydrostatic Testing and EN 10204 3.1 Certificates

Most flange disputes do not start with a failed forging. They start with a certificate that cannot be tied to the part in the crate, or a heat number nobody checked against the stamp on the rim. This guide covers a practical incoming inspection sequence for stainless and alloy steel flanges: what to verify physically, how PMI fits in, what a hydrostatic test proves, and how to read an EN 10204 3.1 certificate without assuming that a document equals conformity.

Why Flange Inspection Is Not a Checklist

Inspection is a chain of evidence, and each step answers a different question. Markings answer "is this the part that was ordered?" Dimensions answer "will it fit and seal?" PMI answers "is it the alloy that was ordered?" Pressure and non-destructive testing answer "is the material sound?" Documentation answers "can we still prove all of this in three years?"

The most common failure is not a missing test. It is a review that stops after step one: the certificate is filed, the packing list is signed, and the part is never compared against either. Separating document review from physical verification catches the mix-ups a paper check passes.

What to Verify on a Stainless Flange

Markings and heat identification

Check the grade, pressure class, nominal size, manufacturer's mark and heat number, and confirm they are legible and consistent. The heat number on the flange is the only reliable link to the certificate, so record it at receiving rather than trusting the tag on the bundle. Paint, protective coating, passivation residue and heavy handling marks are the usual reasons a stamp becomes unreadable — read it before the part goes into storage, not after.

Dimensions and facing

For NPS 1/2 to NPS 24, ASME B16.5 fixes the outside diameter, bolt circle, bolt hole count and diameter, thickness, raised face height and bore. Check the dimensions that decide whether the joint assembles: bolt circle and hole spacing, thickness, facing or ring joint groove, and bore concentricity. A flange can measure within tolerance and still fail because the facing was damaged in transit.

Material identity by PMI

Positive material identification confirms that the alloy in your hand is the alloy on the purchase order. On stainless flanges it separates grades that look and machine identically but behave very differently in service. PMI is a chemistry check; it does not confirm heat treatment, mechanical properties or grain size, and it does not replace the certificate.

Surface condition and weld preparation

Look for laps, seams, forging cracks, rolled-in scale and deep tool marks, particularly at the hub-to-flange transition and on weld bevels. On weld neck flanges, verify bevel angle, root face and bore taper against the drawing; on socket weld flanges, verify socket depth and bore. Protective covers on machined faces should be left in place until the joint is made.

PMI: Coverage, Method and Limits

PMI is carried out with handheld X-ray fluorescence (XRF) or optical emission spectrometry (OES). XRF is fast, non-destructive and well suited to verifying chromium, nickel and molybdenum — the elements that separate 304 from 316, or 2205 from 2507. Its limitation matters: XRF does not measure carbon reliably, and carbon is what distinguishes 316 from 316L. If the low-carbon grade is a requirement, ask for OES or rely on the mill analysis in the certificate, and treat XRF as confirmation of alloy family rather than of grade.

Coverage is a commercial decision that belongs in the purchase order. One hundred percent PMI is common where several grades of similar appearance are bought together, where duplex and super duplex are in scope, or where the flange will be welded into a system that cannot be re-verified later. Sampling is defensible on a single-grade order from one heat, provided the plan, instrument and acceptance criteria are recorded. An undocumented PMI result is not evidence.

Hydrostatic Testing: What It Proves and What It Does Not

Flanges are not individually pressure tested as a routine production step; the pressure boundary is proven when the assembled piping system is tested. ASME B31.3 sets the hydrostatic test of a piping system at 1.5 times the design pressure, subject to the code's provisions for temperature correction, test medium and alternative test pressure where the system cannot safely be filled with water.

That test proves the assembled joint — gasket, bolting, facing condition and installation practice — holds. It does not prove the internal soundness of each forging, and it does not substitute for material certification. Where an individual shell test is required, the purchase order must state the test pressure, hold time and acceptance criteria. Control the chloride content of the test water, then drain and dry the system: residual chloride on austenitic stainless is a stress corrosion cracking risk that appears months later, not during the test.

NDT: When Radiography or Penetrant Testing Is Justified

Liquid penetrant and magnetic particle testing find surface-breaking defects; ultrasonic testing finds internal ones; radiography is rarely applied to flanges and is usually disproportionate to the risk. NDT is justified when a supplementary requirement in the material specification is invoked, when the service is critical, or when a previous lot from the same source showed defects. The purchase order must state the method, the extent, the acceptance criteria and who witnesses the test. "NDT performed" without acceptance criteria is not a result, it is a claim.

Certificate Types: 2.1, 2.2, 3.1 and 3.2

EN 10204 defines four inspection document types. Buyers often order a "3.1 certificate" and then accept paperwork that is actually a 2.2.

Reading an EN 10204 3.1 Certificate Line by Line

A 3.1 certificate should let a stranger reconstruct the part. Check that it cites EN 10204 3.1 and the product standard — for forged stainless flanges, typically ASTM A182/A182M — together with the grade, the heat number, the heat treatment condition and the quantity or weight covered by the document. Then compare the chemistry against the specification limits element by element, and the mechanical results (tensile strength, yield strength, elongation, hardness) against the grade requirements.

Confirm the heat number matches the stamp on the flange. Check that results are stated as measured values rather than specification minima, that the certificate covers the lot actually delivered, and that it carries a date and an identifiable signatory. A document that reproduces the specification minima exactly, across several heats, is worth questioning. Where NDT, a shell test or a PMI report was required, those results belong on or with the certificate; if they are absent, the package is incomplete.

A Practical Inspection Sequence for a Purchase Order

• Review the purchase order before shipment: agree the certificate type, PMI coverage, NDT extent and any individual test requirement in writing.
• On arrival, reconcile the packing list, the quantity and the markings against the order.
• Read the heat number on each flange and match it to the certificate before the parts are unpacked into storage.
• Verify the critical dimensions and the sealing face; photograph any damage before it is attributed to installation.
• Carry out PMI to the agreed coverage, recording instrument, operator and results by heat number.
• Cross-check certificate chemistry and mechanicals against the specification, not against the supplier's summary.
• Witness or review NDT and pressure testing where specified, against written acceptance criteria.
• File the complete dossier — order, certificate, PMI, dimensional record, test reports — under the heat number, and quarantine anything nonconforming before it reaches the pipe rack.

Conclusion

Inspection is not a single event at the end of production. It begins when the purchase order states what evidence is required, and ends only when that evidence has been reconciled with the parts in the warehouse. Three questions matter: does the marking match the certificate, does the chemistry match the grade, and does the dossier survive an audit two years from now?

If you are sourcing stainless or alloy steel flanges with a defined documentation package, send the specification, size, pressure class, facing and required certificate type. Our team will confirm the technical route and the inspection records available for the order. Contact us with your flange schedule, or review the alloy steel flange range and our quality control process.

Frequently Asked Questions

Does every stainless flange need PMI?

No. PMI is a risk-control measure, not a universal requirement. It is most valuable when several grades that look alike are bought together, when duplex or super duplex material is involved, or when the flange will be welded into a system where the alloy can no longer be verified. Single-grade orders from one heat can be covered by documented sampling.

Is an EN 10204 3.1 certificate the same as a mill test certificate?

Not exactly. A mill test certificate is a general industry term; EN 10204 3.1 is a defined document type that must carry specific test results for the delivered lot and be issued by the manufacturer's inspection representative, independent of the manufacturing departments. The two are often the same document in practice, but only the EN 10204 designation tells you what the paper actually guarantees.

Can a stockist or trader issue a 3.1 certificate?

A 3.1 certificate originates with the manufacturer of the product. A stockist or trader can pass on the original certificate for material it resells, but it cannot issue a 3.1 certificate in its own name for material it did not produce. If the document in the crate is headed by a trading company, ask for the original manufacturer's certificate behind it.

At what pressure should a flange joint be hydrotested?

For a piping system designed to ASME B31.3, the hydrostatic test pressure is normally 1.5 times the design pressure, adjusted for test temperature and subject to the code's limits on stresses and on the test medium. Where a system cannot be water tested, the code allows alternatives, but those must be agreed and documented rather than assumed.

How long should flange inspection records be kept?

Retention is set by the project specification, the end user's quality system and any applicable regulatory regime, and it often runs for the life of the installation. Keep the full dossier — certificate, PMI, dimensional record and test reports — linked to the heat number, so a future inspection can retrieve it without reconstructing the purchase.

This article provides general information only. Final material selection, inspection scope and acceptance criteria must be based on the applicable codes and standards, the project specification, and confirmation by qualified engineering personnel.