What ASTM A387 Grade 22 Steel Plate Is
ASTM A387 Grade 22 is a chromium-molybdenum alloy steel plate rolled for welded boilers and pressure vessels that operate at elevated temperature. The grade is published in ASTM A387/A387M and matches ASME SA387 Grade 22 in chemical and mechanical requirements, so plate certified to either specification is normally accepted against the other. The 2.25% chromium and 1% molybdenum combination is what gives the steel its creep strength, its resistance to high-temperature oxidation and its resistance to hydrogen attack in refinery service.
Plate is delivered as-rolled, normalized, or normalized-and-tempered. The specification defines two classes: Class 1, which may be supplied normalized, and Class 2, which must be normalized and tempered and carries the higher tensile requirements.
Chemical Composition
| Element | Content, % | Element | Content, % |
|---|---|---|---|
| Carbon, C | 0.05–0.15 | Silicon, Si | 0.50 max |
| Manganese, Mn | 0.30–0.60 | Chromium, Cr | 2.00–2.50 |
| Phosphorus, P | 0.035 max | Molybdenum, Mo | 0.90–1.10 |
| Sulfur, S | 0.035 max | Balance | Iron |
The chromium range is what separates Grade 22 from Grade 11 (1.00–1.50% Cr) and gives the plate its better scaling resistance above 500 °C. Molybdenum at about 1% raises the elevated-temperature yield strength and suppresses creep deformation, which is why the 2.25Cr-1Mo composition has been the workhorse alloy of hydroprocessing units for decades.
Mechanical Properties and Classes
| Class | Delivery condition | Tensile strength | Yield strength, min | Elongation, min |
|---|---|---|---|---|
| Class 1 | As-rolled or normalized | 380–550 MPa | 230 MPa | 18% |
| Class 2 | Normalized and tempered | 515–690 MPa | 310 MPa | 18% |
Values are specification minima for plate in the condition shown; tension testing follows ASTM A370. Because Class 2 is always normalized and tempered, it is the usual choice for thick plate and for components that will be formed and welded before post-weld heat treatment.
Grade 11 and Grade 22 Compared
Composition: Grade 11 carries about 1.25% chromium with 0.50% molybdenum; Grade 22 carries 2.25% chromium with 1.00% molybdenum.
Strength: at Class 1 the minimum yield strength rises from 205 MPa for Grade 11 to 230 MPa for Grade 22; at Class 2 both grades require 310 MPa minimum yield but Grade 22 holds its strength better as temperature increases.
High-temperature behaviour: the higher chromium and molybdenum content of Grade 22 gives greater resistance to creep and to oxidation, so it is specified where metal temperatures exceed the practical limit of Grade 11.
Applications: Grade 11 suits moderately loaded boiler and pressure-vessel parts; Grade 22 is selected for hydrocrackers, hydrotreaters, hot-wall reactors and steam systems in power generation.
Cost: Grade 22 plate costs more because of its alloy content, so it is normally reserved for the parts that actually see the severe conditions.
Heat Treatment, Welding, Fabrication and Supply
Normalizing: typically carried out between 900 °C and 960 °C, followed by air cooling.
Tempering: normally between 690 °C and 760 °C, with the exact temperature set so that the required strength is met while toughness is preserved.
Welding: preheating in the range 150–200 °C is standard practice; matching 2.25Cr-1Mo consumables and controlled interpass temperature limit cracking in thick sections.
Post-weld heat treatment: usually required, commonly between 690 °C and 730 °C, particularly for sections above about 20 mm.
Inspection: plates can be supplied with ultrasonic examination to A435/A435M, A577/A577M or A578/A578M, and general requirements follow A20/A20M. Thickness-direction testing Z15, Z25 or Z35 is available for heavily welded joints.
Typical applications
ASTM A387 Grade 22 plate is used for hydrocracking and hydrotreating reactors, hot high-pressure separators, heat exchangers, boiler drums, steam headers, coal gasification vessels, ammonia and methanol synthesis equipment, and heavy-wall piping components where elevated-temperature strength and hydrogen resistance are both required.
Plates are produced from 6 mm up to about 200 mm in thickness, in widths up to roughly 3,000 mm, supplied as-rolled, normalized or quenched and tempered, with options for charpy impact testing, ultrasonic examination, edge preparation, shot blasting and shop primer. Sour-service and low-temperature variants of the same 2.25Cr-1Mo family can be discussed against the applicable code requirements of the project.
Frequently Asked Questions
Q: What is the difference between A387 Grade 22 Class 1 and Class 2?
Class 1 may be supplied as-rolled or normalized and has a minimum yield strength of 230 MPa; Class 2 must be normalized and tempered and requires a minimum yield strength of 310 MPa with tensile strength of 515–690 MPa.
Q: Is ASTM A387 Grade 22 the same as ASME SA387 Grade 22?
The two specifications carry the same chemistry and mechanical requirements, so plate qualified to one is normally accepted against the other without further testing.
Q: What chromium and molybdenum content does Grade 22 contain?
Chromium is specified at 2.00–2.50% and molybdenum at 0.90–1.10%, with carbon between 0.05% and 0.15% and manganese between 0.30% and 0.60%.
Q: Can Grade 22 plate be used in hydrogen service?
Its 2.25Cr-1Mo composition is widely used in hydroprocessing equipment because it resists hydrogen attack at elevated temperature; the acceptable temperature and hydrogen partial pressure are governed by the applicable design code for the project.
Q: Does A387 Grade 22 plate need post-weld heat treatment?
Yes. Post-weld heat treatment is normally specified, typically between 690 °C and 730 °C, to soften the weld heat-affected zone and restore toughness in thick sections.
Q: What thickness range is available?
Plates are commonly rolled from 6 mm to 200 mm in thickness and up to about 3,000 mm in width, with ultrasonic examination and impact testing supplied on request.
