MTC for Carbon Steel Pipes: Key Values
The MTC for carbon steel pipes reports the chemical composition, mechanical properties, and test results that confirm compliance with the applicable material specification. For the most commonly used grades in oil and gas piping, including ASTM A106 Gr. B, ASTM A333 Gr. 6, and API 5L Gr. B, specific key values on the mill test certificate must be reviewed and verified before the pipe is accepted for fabrication or installation.
Carbon Steel Pipe MTC: Key Values to Verify
| Parameter | ASTM A106 Gr. B | ASTM A333 Gr. 6 | API 5L Gr. B (PSL2) |
|---|---|---|---|
| Carbon (C) max | 0.30% | 0.30% | 0.24% (seamless) |
| Manganese (Mn) max | 0.29-1.06% | 0.29-1.06% | 1.20% |
| Phosphorus (P) max | 0.035% | 0.035% | 0.025% |
| Sulfur (S) max | 0.035% | 0.035% | 0.015% |
| Silicon (Si) max | 0.10% min | 0.10% min | 0.45% |
| Carbon equivalent (CE) | Not required | Not required | 0.43% max (IIW formula) |
| Yield strength min | 240 MPa (35 ksi) | 240 MPa (35 ksi) | 245 MPa (35.5 ksi) |
| Tensile strength min | 415 MPa (60 ksi) | 415 MPa (60 ksi) | 415 MPa (60 ksi) |
| Elongation min (2 in.) | 30% (standard specimen) | 30% | Per API 5L Table 7 |
| Impact test | Supplementary only | Mandatory at -46 deg. C | Mandatory (PSL2) |
| Hardness max (sour service) | 22 HRC / 248 HBW | 22 HRC / 248 HBW | 22 HRC / 248 HBW |
| Hydrostatic test | Mandatory | Mandatory | Mandatory |
Key Points for MTC Review
Chemistry verification: Cross-check every reported element against the ASTM or API standard limits. Pay particular attention to carbon, sulfur, and phosphorus, as values exceeding the maximum indicate non-conformance. For sour service applications per NACE MR0175, additional restrictions apply: carbon equivalent must be calculated (CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15) even when not required by the base standard.
Mechanical properties: Verify that yield strength, tensile strength, and elongation all meet or exceed the minimum values in the standard. For carbon steel pipe materials, also check that the yield-to-tensile ratio does not exceed 0.93 for API 5L PSL2, as an excessively high ratio indicates reduced ductility.
Heat treatment condition: The MTC must state the heat treatment condition. ASTM A106 pipes are supplied hot-finished or cold-drawn with a normalizing heat treatment. Verify that the reported condition matches the purchase order requirement, as this directly affects mechanical properties and weldability.
Low-temperature service: ASTM A333 Gr. 6 requires Charpy impact testing at -46 deg. C with minimum absorbed energy of 18 J (individual) or 20 J (average). Verify these values on the MTC for any low-temperature piping application. Pipes without documented impact test results cannot be used in services below -29 deg. C.
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