What SA285 Grade C Steel Plate Is
ASME SA285 Grade C is the highest-strength grade in the ASME SA-285/SA-285M carbon steel plate specification, which is technically identical to ASTM A285/A285M. The grade is a carbon steel intended for fusion-welded pressure vessels, boilers and similar containment equipment working at low to moderate pressure. It offers the greatest tensile strength and yield strength of the three SA285 grades while remaining fully weldable without alloy additions, which keeps fabricated cost low for large vessels.
Compared with SA285 Grade A and SA285 Grade B, Grade C allows thinner plate to be used for the same design pressure. The trade-off is slightly lower elongation and a marginally higher carbon level, so forming severity should be reviewed when the plate is to be cold formed into small-diameter shells or dished heads.
Chemical Composition of SA285 Grade C
The heat-analysis limits below apply to SA285 Grade C plate. As with the other grades of the specification, product-analysis tolerances slightly wider than the heat-analysis values are permitted.
| Element | Requirement, % (heat analysis) |
|---|---|
| Carbon, C | 0.28 max |
| Silicon, Si | 0.08 - 0.45 |
| Manganese, Mn | 0.90 max |
| Phosphorus, P | 0.035 max |
| Sulphur, S | 0.035 max |
The carbon ceiling of 0.28 % is the principal difference from Grade B; it is what raises the strength level of the grade. Sulphur and phosphorus are limited to 0.035 % each so that the plate retains adequate toughness after welding and forming.
Mechanical Properties of SA285 Grade C
| Property | Requirement |
|---|---|
| Yield strength, min | 205 MPa |
| Tensile strength | 380 - 515 MPa |
| Elongation, min, 200 mm gauge length | 23 % |
| Elongation, min, 50 mm gauge length | 27 % |
The minimum yield strength is 205 MPa and the tensile strength falls between 380 MPa and 515 MPa, the highest window in the SA285 family. Elongation minima are 23 % on a 200 mm gauge length and 27 % on a 50 mm gauge length, which is still generous enough for most vessel-forming operations.
Grade Comparison and Size Range
| Grade | Yield min, MPa | Tensile, MPa | Carbon max, % |
|---|---|---|---|
| SA285 Grade A | 165 | 310 - 450 | 0.17 |
| SA285 Grade B | 185 | 345 - 485 | 0.22 |
| SA285 Grade C | 205 | 380 - 515 | 0.28 |
Thickness: 5 mm - 300 mm
Width: 1500 mm - 4200 mm
Length: 3000 mm - 18000 mm
Rolling type: boiler plate and pressure vessel plate
Delivery condition: as-rolled, normalised, or stress relieved
Welding, Forming and Applications
SA285 Grade C welds with conventional carbon steel consumables and does not call for preheat in light sections; heavier or highly restrained joints benefit from a controlled preheat and interpass temperature. Cold forming is common for shells and heads, and stress relieving after forming keeps fabricated dimensions stable.
Pressure vessel shells, heads and drums
Storage tanks in petroleum and natural gas service
Chemical, petroleum and gas plant equipment
Boiler components and low-pressure steam equipment
General welded containment structures
Because the grade has no alloy content, it is not intended for elevated-temperature or corrosive service where chrome-molybdenum or manganese-molybdenum plate is normally specified.
Frequently Asked Questions
Q: What is the tensile strength of SA285 Grade C?
The tensile strength range is 380 MPa to 515 MPa, with a minimum yield strength of 205 MPa.
Q: Is SA285 Grade C better than Grades A and B?
It is stronger, not automatically better. Grade C suits higher design pressures through thinner plate, while Grades A and B offer slightly better elongation and are usually cheaper for low-pressure work.
Q: Is SA285 Grade C the same as ASTM A285 Grade C?
Yes. The ASME SA-285/SA-285M and ASTM A285/A285M specifications are technically identical, including the Grade C requirements.
Q: Where is SA285 Grade C normally used?
It is commonly used for pressure vessel shells, storage tanks in the petroleum and natural gas industries, and industrial equipment in chemical and gas plants.
Q: What delivery conditions are available?
Plate is supplied as-rolled, normalised or stress relieved, and the condition must be specified on the purchase order.
Q: Can SA285 Grade C be used at elevated temperature?
It is a plain carbon steel for low to moderate pressure and near-ambient service; elevated-temperature duty is normally handled by SA302 or SA387 grades instead.
