Every pressure vessel plate you order to SA-516, SA-537, SA-204, SA-387, or any other ASME Section II plate material specification is governed by two standards simultaneously: the product spec that gives it its grade and properties, and ASTM A20, which establishes the general requirements for how that plate is tested, documented, and certified.
If your MTC for SA-516 Grade 70 doesn't reference ASTM A20 (or its ASME equivalent, the Section II general requirements for carbon steel plate), your cert is missing its governing framework. The ASME authorized inspector will find this, and the conversation will not be brief.
What ASTM A20 Actually Covers
ASTM A20 / ASME SA-20 is the general requirements standard for steel plates used in pressure vessel fabrication. It covers:
Mechanical testing requirements. A20 specifies test frequencies, specimen orientation (longitudinal vs. transverse), specimen dimensions, and the test temperatures for impact testing. For each plate product, A20 defines how many tension tests per heat are required, whether tests must come from each plate or per heat, and how samples must be cut and oriented.
Heat treatment documentation. When a product spec requires heat treatment — normalizing, quenching and tempering, or stress relieving — A20 specifies what the MTC must document: the heat treatment process applied, the temperature range, and the condition (normalized, Q&T). This documentation is mandatory. A cert that says "as-rolled" for a product spec that requires normalized delivery is nonconforming regardless of what the mechanical values show.
Chemistry certification requirements. A20 requires product analysis (heat analysis plus product check analysis or waiver) to be reported on the cert. For most standard orders, heat analysis is sufficient. When supplementary requirement S18 (product analysis) is invoked, the mill must perform and report product analysis for each plate.
Marking requirements. A20 specifies how pressure vessel plate must be marked: the ASTM/ASME designation, grade, heat number, plate number, heat treatment condition, mill name, and applicable supplementary requirement designations.
Permissible variations. Thickness tolerances, flatness tolerances, length and width tolerances for pressure vessel plate — these live in A20, not in the product spec. If you're disputing a dimensional tolerance issue with a supplier, A20 is where the acceptance criteria come from.
Mandatory Supplementary Requirements: S1 Through S14
A20 includes 18 supplementary requirements (S1–S18) that buyers can invoke on their PO. When invoked, these must be documented on the MTC:
S1 — Vacuum treatment: The steel was vacuum-degassed, reducing hydrogen content. Required for many hydrogen service applications and high-alloy grades.
S4 — Charpy V-notch impact testing: The specific test temperature and minimum absorbed energy must appear on the cert. If your PO specifies impact testing at -40°F with 15 ft-lbf minimum transverse average, those results must be on the MTC.
S5 — Ultrasonic examination: Each plate was examined by UT per the referenced standard (A578). The cert should reference the examination standard, the acceptance level, and confirm compliance.
S7 — Carbon equivalent requirement: The carbon equivalent formula (typically Pcm or IIW formula) must be reported. Required by many pipeline and pressure vessel specs for weldability assurance.
S9 — Simulated post-weld heat treatment of mechanical test coupons: The mechanical properties on the cert were obtained from specimens that have been heat-treated to simulate PWHT. Required when your fabrication PWHT might affect properties.
When your PO invokes supplementary requirements and the MTC doesn't reference them, one of three things happened: the mill didn't perform the testing, the service center sourced from stock that wasn't ordered to those requirements, or the cert was issued without including the supplementary results. All three are problems. The resolution requires either a supplemental cert from the mill confirming the testing was done, or rejection and reorder.
What a Compliant A20 Cert Looks Like vs. a Generic Cert
A generic pressure vessel plate cert might show: material description, heat number, chemistry, yield/tensile/elongation. That's the minimum data many mills put on a cert for stock material.
A compliant A20 cert for a specific PO shows: ASTM A516 Grade 70 / ASME SA-516 Grade 70, heat number, plate number, heat treatment condition (normalized), heat analysis chemistry against A516 Table 1 limits, mechanical test results with specimen orientation and gauge length, test frequency compliance (per A20 testing requirements), applicable supplementary requirements with test results for each, authorized mill certification signature, and A20 / SA-20 reference.
The difference is not just completeness. A properly A20-compliant cert documents the chain of custody from the melting heat through the mechanical test report. When the ASME authorized inspector reviews the material cert package for a Section VIII vessel, they are checking that the cert demonstrates compliance to the complete standard — not just the product spec values.
What ASME Inspectors Check
ASME Authorized Inspectors (AIs) reviewing cert packages for pressure vessel Code stamps follow a standard review sequence. For plate material:
- Material spec and grade match the design document
- A20 / SA-20 referenced (or applicable ASME general requirements)
- Heat number present and traceable to the vessel traveler
- Heat analysis chemistry within product spec limits
- Mechanical test results present with test conditions
- Heat treatment condition documented if required by product spec
- Supplementary requirements invoked on PO present on cert with results
- Mill certification signature present
A cert that fails any of these checks is an NCR against the vessel job. The AI won't stamp the vessel with open NCRs. Resolution takes time, and if the material needs to be rejected and reordered, it takes much more than time.