What SA299GrA Covers
SA299GrA is a carbon-manganese-silicon steel plate intended for welded boiler and pressure vessel components, and it is specified in ASME SA-299/SA-299M, the ASME material specification for carbon-manganese-silicon steel plates for pressure vessels. The specification contains two grades, Grade A and Grade B, which differ in their specified tensile and yield requirements but share the same broad alloy concept. Grade A is the lower-strength of the two and is the grade normally chosen when the design temperature stays within the medium-temperature range typical of boiler drums and headers, generally taken as service not exceeding about 400 C. The steel is required to retain adequate strength at that temperature while remaining tough and weldable at ambient conditions during fabrication.
Delivery Condition and Steelmaking Practice
SA299GrA plate may be supplied either normalized or as-rolled, but the normalized condition is standard practice for heavier plate, and it is the usual requirement for thicknesses of roughly 50 mm and above. Normalizing refines the ferrite-pearlite grain structure, which is what allows the plate to satisfy both the tensile requirements and the impact requirements at one and the same time. The steel is fully killed and produced to fine grain practice in accordance with ASTM A20/A20M, the general requirements specification that governs steel plates for pressure vessels. In practice that means deoxidation with aluminium or an equivalent grain-refining addition, plus a verified fine austenitic grain size on the finished plate. Because the inclusion content is controlled, plate thickness direction properties are uniform and segregation of alloying or residual elements is limited, which matters for the heavy section welds used in boiler construction.
Chemical Composition of SA299 Grade A
The specification sets limits that depend on plate thickness, because heavier sections need slightly more carbon and manganese to reach the required strength after normalizing. The table below summarises the limits for the two thickness groups.
| Element | Thickness 25 mm and under | Thickness over 25 mm |
|---|---|---|
| C, max | 0.28 | 0.30 |
| Si | 0.13 - 0.45 | 0.13 - 0.45 |
| Mn | 0.84 - 1.52 | 0.84 - 1.62 |
| P, max | 0.035 | 0.035 |
| S, max | 0.035 | 0.035 |
Silicon is a deliberate addition rather than a residual: it raises strength in the normalized condition and improves resistance to oxidation at elevated temperature. Carbon and manganese provide the basic strength, while phosphorus and sulphur are held to low limits because both reduce toughness and weldability. Silicon content should not be allowed to fall below the minimum, since the specification treats it as a strengthening element in this grade.
Mechanical Properties of SA299 Grade A
The tensile and yield requirements apply to the plate as delivered and are verified on test pieces taken in accordance with the general requirements of ASTM A20/A20M. Minimum yield strength also steps down with thickness.
| Property | Thickness 25 mm and under | Thickness over 25 mm |
|---|---|---|
| Yield strength, min (MPa) | 290 | 275 |
| Tensile strength (MPa) | 515 - 655 | 515 - 655 |
| Elongation, min (%), 50 mm gauge length | 16 | 16 |
| Elongation, min (%), 200 mm gauge length | 19 | 19 |
The high tensile-to-yield ratio of this grade is characteristic of normalized carbon-manganese pressure plate: it offers generous tensile strength, which suits the membrane stress in a boiler drum, while keeping enough ductility for the roll forming and welding operations that follow.
Welding and Fabrication
Welding processes: shielded metal arc, submerged arc and gas metal arc welding are all used in boiler shop practice. Submerged arc welding is common for longitudinal and circumferential drum seams.
Consumables: filler metals are matched to the tensile class of the parent plate, and low-hydrogen consumables are preferred for thick, restrained joints to avoid hydrogen-assisted cracking.
Preheat: preheat and interpass temperatures are set from plate thickness, restraint and carbon equivalent. Thick sections and highly restrained nozzle welds need controlled heating rather than ambient-temperature welding.
Post-weld heat treatment: PWHT is applied as required by the governing construction code for the material group concerned, with the soaking temperature selected so that strength is retained while residual stresses are relieved.
Forming: cold rolling and pressing of drum shells and head plates proceed normally; hot forming is carried out within the normalizing range and followed by controlled cooling so that the specified properties are restored.
Inspection: the mill test certificate should record the heat analysis, the tension test results and the impact results, and the delivered plate should be verified against the specification for the grade and thickness concerned.
Applications
The principal use of SA299GrA is in boiler and pressure equipment manufacture: steam drum shells and heads, headers, steam and water separators, and thick-walled pressure vessels operating at medium temperature and moderate pressure. It is also used for large welded storage and process vessels where the design temperature is within the range for which the grade is qualified and where a normalized, tough carbon-manganese steel is adequate without the cost of an alloy steel. Because the specification is an ASME one, the plate is most often ordered for equipment built to the ASME Boiler and Pressure Vessel Code, and the allowable stress values used in design come from the tables of that code for the specific grade and temperature involved.
Frequently Asked Questions
Q: What is the difference between SA299GrA and SA299GrB?
Both grades are carbon-manganese-silicon boiler plate of ASME SA-299/SA-299M. Grade B has higher specified tensile and yield strength requirements than Grade A, which allows a thinner wall for the same design pressure, while Grade A is used where the higher strength is not needed.
Q: Which standard governs SA299GrA?
ASME SA-299/SA-299M, together with the general requirements of ASTM A20/A20M for plates for pressure vessels. The two documents together set the chemistry limits, the heat treatment and the mechanical test requirements.
Q: Is SA299GrA supplied normalized or as-rolled?
Either condition is permitted by the specification, but the normalized condition is normal practice for heavier plate and is the usual requirement for thicknesses of about 50 mm and above.
Q: Why is silicon specified in SA299GrA?
Silicon is added deliberately in this carbon-manganese-silicon steel. It contributes strength in the normalized condition and improves oxidation resistance at elevated temperature, so the specified minimum content must be met.
Q: What is the maximum service temperature?
The grade is intended for medium-temperature service, commonly taken as approximately 400 C and below for the welded components concerned. The allowable stress for a specific design temperature must be taken from the applicable construction code tables.
Q: How is SA299GrA welded?
Conventional arc processes with tensile-matched, low-hydrogen consumables are used, with preheat and interpass temperature controlled according to thickness and restraint. Post-weld heat treatment is applied when required by the construction code for the relevant material group.
