What Is ASTM A202 Grade A Steel Plate?
ASTM A202 is a specification for chromium-manganese-silicon alloy steel plates intended mainly for welded boilers and other pressure vessels. The standard covers two grades, A and B, each treated as a separate material with its own chemistry and strength limits, and it fixes the maximum plate thickness at 2 in. [50 mm].
ASTM A202 Grade A is also approved for rivets: when the steel is used for that purpose, the bars supplied must meet the additional requirements for hot rolled bars given in the same specification. This dual role makes the grade useful for boiler drums, shells, headers and similar pressure retaining parts where plate and rivet material come from the same specification.
Scope and Thickness Limits of ASTM A202
The specification defines chromium-manganese-silicon alloy steel plates with the following scope:
Standard: ASTM A202 / A202M
Grades covered: Grade A and Grade B
Intended service: welded boilers and other pressure vessels
Maximum plate thickness under the specification: 2 in. (50 mm)
Delivery condition: as rolled, or normalised when ordered
Rivet application: Grade A bars supplied to the hot rolled bar requirements of the specification
Plate outside this thickness range falls under other specifications, so purchase documents should state the thickness and the standard together. A mill may be able to roll and supply wider or heavier plate from the same steel family, but that product is not covered by the A202 thickness limit.
Chemical Composition of A202 Grade A
| Element (%) | C max | Si | Mn | P max | S max |
|---|---|---|---|---|---|
| A202 Grade A | 0.17 | 0.54-0.90 | 0.97-1.52 | 0.035 | 0.035 |
The chemistry is built around manganese and silicon with a cap on carbon. Low carbon keeps the plate weldable and tough after welding, manganese provides solid solution strengthening and hardenability, silicon supports strength at temperature, and chromium in the alloy system improves resistance to oxidation and scaling in boiler service.
For pressure vessel design, the carbon equivalent is used to judge weldability and to plan preheating. It is calculated as Ceq = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15, expressed in percent.
Mechanical Properties of A202 Grade A
| Thickness (mm) | Min yield strength (MPa) | Tensile strength (MPa) | Min elongation (%) |
|---|---|---|---|
| 6-50 | 310 | 515-655 | 19 |
| 50-100 | 310 | 515-655 | 16 |
The specified tensile range is narrow by pressure vessel standards, which keeps design calculations predictable. Elongation requirements fall as thickness increases, reflecting the lower through thickness ductility of heavier plate. Yield strength is quoted as a minimum, so the designer can rely on at least 310 MPa while the actual value is normally higher.
Fabrication of A202 Grade A Plate
Cutting: plasma, laser, waterjet or machining, with edges cleaned before welding
Forming: cold forming is possible for moderate radii; hot forming needs temperature control to avoid property loss
Welding: low hydrogen consumables, preheat based on carbon equivalent and thickness, and interpass temperature control
Heat treatment: normalising is used when the specification or the purchaser requires it
Inspection: chemical analysis, tensile testing and, when specified, impact and hardness testing
Because these plates operate under pressure, welding procedure qualification and non-destructive examination of the joints are as important as the plate properties themselves. Fabricators normally work to a construction code that defines the preheat, the consumables and the extent of radiography or ultrasonic testing for each joint type.
Typical Applications
ASTM A202 Grade A plate is used for shells and heads of welded boilers, pressure vessel drums, headers, accumulators, storage tanks for non corrosive service, and heavy fabricated structures that combine pressure with mechanical load. Rivet and stay bolt applications in older boiler designs also fall within the scope of the grade.
Service temperature and the corrosivity of the process fluid decide whether the steel is suitable. A202 plates are intended for moderate temperature pressure service, and where aggressive media or high temperature creep conditions apply, a different specification should be selected at the design stage.
Frequently Asked Questions About ASTM A202 Grade A
Q: What is ASTM A202 Grade A steel used for?
It is a chromium-manganese-silicon alloy steel plate designed mainly for welded boilers and other pressure vessels, and Grade A is also suitable for rivets when the bars meet the hot rolled bar requirements of the specification.
Q: What is the maximum thickness allowed by ASTM A202?
The specification limits plate thickness to 2 in. [50 mm]. Materials above that thickness must be ordered under a specification that covers them.
Q: What are the typical mechanical properties of A202 Grade A?
Minimum yield strength of 310 MPa with a tensile strength range of 515-655 MPa and a minimum elongation of 19 % for 6-50 mm plate, falling to 16 % elongation for heavier material.
Q: How does the carbon equivalent affect fabrication?
The carbon equivalent calculated from carbon, manganese, chromium, molybdenum, vanadium, nickel and copper indicates how the steel will behave during welding. Higher values call for more preheat and tighter heat input control.
Q: Is A202 Grade A the same as Grade B?
No. Both grades belong to the same specification but are separate materials with their own limits. Substitution between them requires a check of strength, thickness and application requirements.
Q: What sizes can be supplied?
Plate for the A202 thickness limit of up to 50 mm is readily available. Heavier plate, wider widths and cut to size shapes from the same alloy family can also be produced by the mill for projects that specify them.
