What ASME SA612 Plate Is Designed For
ASME SA612/SA612M covers killed carbon manganese silicon steel plates intended for welded pressure vessels operating at moderate and lower temperatures. It is the ASME Section II material specification and is identical in technical content to ASTM A612/A612M, the letter M marking the metric edition of the combined designation. Ordinary structural carbon plate is not intended for pressure retaining service and is not qualified against the same requirements, which is the reason this specification exists.
Mechanical Properties Compared with Standard Carbon Plate
The grade is fully killed and made to a fine austenitic grain size, which is what gives it notch toughness at low temperature together with a strength level above the ordinary pressure vessel carbon steels.
| Property | ASME SA612/SA612M | Structural carbon plate (A283 Grade C type) |
|---|---|---|
| Minimum yield strength | 345 MPa (50 ksi) | 205 MPa (30 ksi) |
| Tensile strength | 570-725 MPa (81-105 ksi) | 380-515 MPa (55-75 ksi) |
| Deoxidation and grain size | Fully killed, fine austenitic grain size | Not specified |
| Impact testing | Required by the specification | Not a standard requirement |
| Design framework | ASME BPVC Section VIII, allowable stresses from Section II Part D | Structural design codes |
The specification limits plate thickness to 25 mm (1 in.). Thicker material in the same strength class must be ordered to a different specification, and that limit is a frequent surprise when the grade is written into the design of a heavy wall drum.
Chemistry and How It Is Controlled
The chemistry is deliberately simple: low carbon with a manganese range for strength and silicon for deoxidation, held to low phosphorus and sulphur limits so that toughness and weldability are preserved. Heat analysis limits include carbon 0.25 percent maximum, manganese 1.00 to 1.50 percent, silicon 0.15 to 0.50 percent, phosphorus 0.025 percent maximum and sulphur 0.025 percent maximum, with copper, nickel, chromium, molybdenum and vanadium each held to residual maxima. The heat analysis is reported on the mill certificate and the product analysis is verified against the specification limits, because on a pressure vessel the certificate forms part of the design documentation rather than routine shipping paperwork.
Fabrication, Welding and Inspection
SA612 plate is designed for welded construction. Low carbon combined with fully killed fine grain practice keeps the heat affected zone narrow and reduces the risk of cold cracking, while low sulphur and phosphorus reduce the risk of lamellar tearing in restrained joints. Preheat is not normally required for thin plate in mild workshop conditions, but thick sections, high restraint and low ambient temperature call for a preheat consistent with the qualified welding procedure. Consumables are selected to match the strength of the plate so that the weld metal does not undermatch it, and any weld repair on the plate itself, before or after delivery, must follow ASME SA20/SA20M and be approved by the authorised inspector.
Plates are supplied under the general requirements of ASME SA20/SA20M, which govern testing, retesting, dimensional tolerances, marking and repair procedures. The delivery condition should be stated on the order: as-rolled, normalised, stress relieved, or normalised and stress relieved. Each plate carries the specification designation, grade, heat number, size and manufacturer identification, and those markings must match the mill certificate and the order. Dimensions are checked against the tolerance tables, the surface is examined for laminations, seams and handling damage, and ultrasonic examination is ordered where the design requires it.
Frequently Asked Questions
Q: Is SA612 the same as A612?
A: The technical content is identical. A612 is the ASTM designation and SA612 is the ASME designation assigned to the same specification for use under the ASME Boiler and Pressure Vessel Code, with the M suffix marking the metric edition.
Q: Why choose SA612 instead of ordinary carbon steel plate for a pressure vessel?
A: It offers a specified minimum yield strength of 345 MPa against about 205 MPa for structural carbon plate, it is fully killed and fine grained, and it is impact tested and documented under the pressure vessel general requirements. Thinner plate can therefore be used for the same design pressure with a documented safety margin.
Q: What is the maximum thickness covered by the specification?
A: Plate up to 25 mm (1 in.) in thickness. Heavier plate in the same strength class must be ordered to another specification, so the limit should be checked before the grade is written into a design.
Q: Does the upper limit of the tensile range apply?
A: Yes. The specified tensile range of 570 to 725 MPa has both a minimum and a maximum, and a plate that tests above the maximum is not acceptable under the specification.
Q: Which general requirements apply to SA612 plates?
A: ASME SA20/SA20M, covering testing, retesting, dimensional tolerances, quality, repair of defects and marking. The heat analysis is reported on the mill certificate, and the certificate is retained with the vessel records.
Q: Can SA612 plate be stress relieved after fabrication?
A: Yes. Normalised, stress relieved, or normalised and stress relieved plate can be ordered as the delivery condition, and post weld heat treatment after fabrication is carried out in accordance with the design code and the qualified procedure.
