SA-387 Chrome-Moly Plate and 12Cr1MoV: Grades, Classes, Hydrogen Service and Welding

Quick Answer

SA-387 (ASME) and ASTM A387 cover chromium-molybdenum alloy steel plate intended mainly for welded boilers and pressure vessels in elevated-temperature service. The grade number names the alloy: Grade 2 (½Cr-½Mo), 12 (1Cr-½Mo), 11 (1¼Cr-½Mo), 22 (2¼Cr-1Mo), 21 (3Cr-1Mo), 5 (5Cr-½Mo), 9 (9Cr-1Mo) and 91 (9Cr-1Mo with vanadium and niobium). Every grade except 91 comes in two strength classes: Grade 22 Class 1 requires 415–585 MPa tensile and 205 MPa minimum yield, Class 2 515–690 MPa and 310 MPa; Grade 91 is Class 2 only. Plates are annealed (Class 1 only), normalised and tempered or accelerated-cooled and tempered, and the tempering temperature limits the PWHT that follows. In hydrogen service, chromium and molybdenum resist high-temperature hydrogen attack, judged against the Nelson curves of API RP 941, and 2¼Cr-1Mo reactor plate and weld metal are also screened for temper embrittlement with the J-factor, X-bar (weld metal) and step-cooling tests. 12Cr1MoV is a Chinese 1Cr-0.3Mo-0.2V creep-resisting steel; 12Cr1MoVR is its boiler and pressure-vessel plate under GB/T 713. It is approximately comparable to Western Cr-Mo grades, never interchangeable with them.

A typical enquiry reads: "SA-387 Gr 22, 60 mm plate, 18 tonnes, or Chinese equivalent." It leaves the mill guessing. There is no class, though Class 1 and Class 2 differ by 100 MPa in minimum tensile strength. There is no post-weld heat treatment (PWHT) cycle, which the mill needs before it tempers the plate. Nothing says whether the vessel sees hot hydrogen, which brings impurity limits and step-cooling tests. And "Chinese equivalent" should mean 12Cr2Mo1R, the 2¼Cr-1Mo plate in GB/T 713; an offer of 12Cr1MoVR is a different steel, with vanadium and less than half the chromium.

Chrome-moly plate goes into the parts of a plant that run hot: reactor and separator shells, hot heat-exchanger shells, boiler components and hydrogen equipment. This guide covers the grades and classes, hydrogen service, 12Cr1MoVR and what a complete order contains.

What SA-387 Covers

ASTM A387/A387M, adopted by ASME as SA-387, is the chromium-molybdenum plate specification for welded boilers and pressure vessels in elevated-temperature service. The current ASTM edition lists Grades 2, 12, 11, 22, 21, 5, 9 and 91 (editions up to at least A387-11 also listed the low-carbon Grades 22L and 21L); Grade 911 has moved to a separate specification, A1017/A1017M. The steel must be killed and heat treated. General plate requirements, including tolerances, test methods and the menu of supplementary requirements, come from ASTM A20/A20M.

The same chemistries in other product forms have their own specifications: A335 for pipe (see our guide to A335 chrome-moly pipe), A213 for boiler and heat-exchanger tubes (A213 T11, T22 and T91), and forging specifications for nozzles and flanges. A vessel draws on all of them.

Grades: What the Chromium and Molybdenum Do

Chromium raises oxidation resistance and, with molybdenum, forms carbides more stable than iron carbide. Molybdenum is the main contributor to creep strength. Grade 91 adds vanadium and niobium, which form fine, stable precipitates; its strength depends on correct normalising and tempering, and A387 offers it in two types, Type 2 with a restricted composition for creep resistance.

Class 1 vs Class 2

The class sets the strength level:

Older editions also covered the low-carbon Grades 22L and 21L, available only in Class 1 with the Class 1 values of Grades 22 and 21; they are not in the current scope. Check the current edition for elongation and later changes.

Heat treatment. Plates other than Grade 91 are annealed, normalised and tempered, or, when the purchaser permits, accelerated-cooled from the austenitising temperature (by air blast or liquid quench) and tempered. Annealed plate can only meet Class 1. Minimum tempering temperatures rise with alloy content: 620 °C (1150 °F) for Grades 2, 12 and 11, and 675 °C (1250 °F) for Grade 22. Grade 91 is austenitised at 1040–1080 °C, then normalised or accelerated-cooled, and tempered at 730–800 °C. Check the current edition before quoting these.

Worked example: Class 1 or Class 2 for a 2¼Cr-1Mo shell

A vessel shell has an inside diameter of 2,400 mm, a design pressure of 4.5 MPa (45 bar, 653 psi), a joint efficiency of 1.0 and a 3 mm corrosion allowance. The thin-shell formula of ASME Section VIII Division 1 is:

t = P × R / (S × E − 0.6 × P)

R is the inside radius, 1,200 mm, and S the allowable stress at the design temperature. Assume, for illustration only, that the code's stress table gives 115 MPa for Grade 22 Class 1 and 140 MPa for Class 2 at the design temperature; the real values come from ASME Section II Part D.

• Class 1: 4.5 × 1,200 / (115 − 2.7) = 48.1 mm; plus 3 mm corrosion allowance = 51.1 mm → 52 mm plate
• Class 2: 4.5 × 1,200 / (140 − 2.7) = 39.3 mm; plus 3 mm = 42.3 mm → 43 mm plate

At 7.85 t/m³, a metre of shell weighs π × 2.452 × 0.052 × 7,850 ≈ 3,144 kg in Class 1 and π × 2.443 × 0.043 × 7,850 ≈ 2,591 kg in Class 2. Over a 10 m shell that is 31.4 t against 25.9 t, a saving of about 5.5 t (18%).

The saving exists only where short-term strength sets the allowable stress. Where creep governs, the allowable stresses come from creep and rupture data, and the two classes move close together, so check the table at your design temperature.

Hydrogen Service: High-Temperature Hydrogen Attack

In hot, dry hydrogen service, generally from about 204 °C (400 °F) upward, molecular hydrogen dissociates and atomic hydrogen diffuses into the steel. There it reacts with carbides to form methane. Methane cannot diffuse out: it collects at grain boundaries, and the steel decarburises and fissures. This is high-temperature hydrogen attack (HTHA), and it can progress with little sign at the surface.

Chromium and molybdenum hold carbon in more stable carbides that resist the reaction, so the alloy grades tolerate higher temperatures and hydrogen partial pressures. API RP 941 sets the limits as the Nelson curves: operating temperature against hydrogen partial pressure, one curve per steel. Three points matter to buyers:

• Carbon steel is vulnerable with or without PWHT. Where it falls outside its curve, the next steps up are 1Cr-½Mo and 1¼Cr-½Mo, then 2¼Cr-1Mo, each with a higher curve
• Owners add a margin, because failures have been documented below the curves
• C-½Mo was dropped from the main curves in 1990 after HTHA was reported below its curve

For heavy-wall 2¼Cr-1Mo reactors, purchasers commonly add API RP 934-A, with further requirements such as step-cooling tests and weld hardness limits. A387 does not cover the vanadium-modified 2¼Cr-1Mo-¼V steel, which is bought under other plate and forging specifications.

Temper Embrittlement: J-Factor, X-Bar and Step Cooling

2¼Cr-1Mo and similar steels lose notch toughness when held in, or cooled slowly through, roughly 400–600 °C (TWI's range; others quote slightly lower ones, such as 370–550 °C). Impurities segregate to the prior austenite grain boundaries: antimony, phosphorus, tin and arsenic, in TWI's order of importance. Hardness and tensile strength barely change, but the ductile-to-brittle transition temperature can rise by as much as 100 °C, and fractures turn intergranular. Manganese, nickel and chromium increase susceptibility; small molybdenum additions inhibit it.

The danger comes at start-up and shutdown, when the metal is cold and the vessel under pressure, so operators of embrittled equipment hold pressure down until the metal is above a minimum pressurisation temperature. The cure is clean steel and weld metal, set by three controls:

• J-factor (Watanabe), for plate and weld metal: J = (Mn + Si) × (P + Sn) × 10⁴, with elements in weight per cent. TWI treats J ≤ 180 as low risk; reactor specifications usually set tighter limits
• X-bar (Bruscato), for weld metal: X = (10P + 5Sb + 4Sn + As) / 100, with elements in ppm. TWI treats X below 20 as low risk, and 15 is a common industry requirement
• Step-cooling test: Charpy tests before and after a stepped heat treatment that accelerates embrittlement. TWI quotes the criterion AF + 2.5 × (SC − AF) < 38 °C, where AF and SC are the 54 J transition temperatures before and after step cooling. A387 offers step cooling as a supplementary requirement

Heating above 600 °C and cooling quickly below 300 °C reverses it, but it returns in service; clean steelmaking is the only practical defence.

Worked example: checking the certificates

Plate heat analysis: Mn 0.52%, Si 0.07%, P 0.006%, Sn 0.004%.

J = (0.52 + 0.07) × (0.006 + 0.004) × 10⁴ = 0.59 × 0.010 × 10⁴ = 59

A second plate with Mn 0.55%, Si 0.25%, P 0.015% and Sn 0.010% gives J = 0.80 × 0.025 × 10⁴ = 200, above even TWI's low-risk value. Low silicon and low phosphorus do most of the work.

Weld metal analysis: P 80 ppm, Sb 20 ppm, Sn 40 ppm, As 60 ppm.

X = (10 × 80 + 5 × 20 + 4 × 40 + 60) / 100 = (800 + 100 + 160 + 60) / 100 = 11.2 ppm

Phosphorus supplies more than 70% of the total. Raise it to 120 ppm and X becomes 15.2 ppm, which fails a 15 ppm limit. Specify X-bar on the consumable batch certificate, not just the classification.

12Cr1MoV and 12Cr1MoVR

12Cr1MoV is a Chinese GB designation for a low-alloy chromium-molybdenum-vanadium creep-resisting steel. The name reads as about 0.12% carbon (the leading number is in hundredths of a per cent), about 1% chromium, and smaller additions of molybdenum and vanadium. The suffix names the product: 12Cr1MoVR is the plate for boilers and pressure vessels under GB/T 713, and 12Cr1MoVG the seamless high-pressure boiler tube and pipe under GB/T 5310.

Typical composition limits are C 0.08–0.15%, Si 0.15–0.40%, Mn 0.40–0.70%, Cr 0.90–1.20%, Mo 0.25–0.35%, V 0.15–0.30%, P ≤ 0.025% and S ≤ 0.010%.

Vanadium is the difference from the Western 1–1¼Cr plates: its fine, stable carbides support creep strength with less molybdenum. The tube and pipe forms have a long record in main steam lines. Chinese studies examine 12Cr1MoV piping after 26 years of service, and studies of its Russian counterpart 12Kh1MF, of essentially the same composition, describe lines at about 540 °C and 14 MPa. Long service brings pearlite spheroidisation, carbide coarsening, grain growth and a marked fall in yield and elevated-temperature strength.

For the plate, GB/T 713-2014 (issued as GB 713-2014) gave 12Cr1MoVR a tensile strength in the 430–590 MPa band and a minimum yield from 235 MPa upward, depending on thickness, with at least 19% elongation. The 2014 standard has since been replaced by GB/T 713.2-2023, in force since 1 March 2024, so confirm which edition the mill certifies to.

Is it equivalent? Its closest relative is 12Kh1MF, which a recent study calls an analogue of the German 14MoV6-3, a ½Cr-½Mo-¼V steel used for the same steam-line duty, though with less chromium and more molybdenum. GB/T 713's own counterparts of the A387 grades are 14Cr1MoR (1¼Cr-½Mo, close to Grade 11) and 12Cr2Mo1R (2¼Cr-1Mo, close to Grade 22). ASTM's plates at the same chromium level, Grades 12 and 11, carry more molybdenum and no vanadium: their room-temperature strength is similar, but their creep behaviour and allowable stresses are not. Treat 12Cr1MoVR as approximately comparable to these grades, never as identical. A substitution needs a design code that lists the material with allowable stresses, and a welding procedure qualified on it.

Welding and PWHT

Welding can leave hard, brittle, hydrogen-sensitive martensite in the heat-affected zone (HAZ). Hence preheat, low-hydrogen consumables and PWHT, which TWI notes is mandatory in the application codes for most creep-resisting steels: it softens the HAZ, restores toughness and sets the precipitates that give creep strength.

Typical values published by TWI, based on 5–10 ml of hydrogen per 100 g of weld metal. The code and the qualified procedure govern.

ASME Section VIII Division 1 sets minimum holding temperatures (593 °C for 1Cr-½Mo and 677 °C for 2¼Cr-1Mo, as TWI lists them); EN 13445 sets ranges, such as 670–720 °C for 2¼Cr-1Mo. Hold time is roughly one hour per 25 mm, with a typical minimum of two hours for 2¼Cr-1Mo.

Consumables. Matching low-hydrogen consumables exist for all these steels, such as E8018-B2 electrodes for 1¼Cr-½Mo and E9018-B3 for 2¼Cr-1Mo; dissimilar joints usually take the filler of the less alloyed steel. PWHT is an essential variable in procedure qualification; see our guide to WPS, PQR and welder qualification.

Two rules belong in the plate order:

1. Keep PWHT below the plate's tempering temperature, or prove the properties by testing. For Grade 22 the margin is tight: TWI's typical PWHT range starts at 680 °C, and A387's minimum tempering temperature is 675 °C. The mill must know your cycle to temper above it.
2. State the total PWHT the plate will see, including repair cycles, and order mechanical tests on coupons given a simulated PWHT, so the certificate represents the steel after fabrication.

12Cr1MoV. TWI notes that vanadium-bearing low-alloy steels are the most sensitive to reheat cracking during PWHT, and that the related ½Cr-½Mo-¼V steel is conventionally welded with a 2¼Cr-1Mo filler. Qualify the procedure on the actual steel; do not borrow an A387 Grade 11 or 22 procedure.

Ordering Checklist

• Specification, grade and class: ASTM A387 or ASME SA-387, grade and class (Type 1 or 2 for Grade 91); or GB/T 713 12Cr1MoVR and edition
• Heat treatment: normalised and tempered, or accelerated-cooled and tempered; tempering temperature on the certificate
• Dimensions: thickness (nominal or minimum), width, length, quantity
• Design data: code, design temperature and pressure, hydrogen partial pressure, and whether API RP 941 or 934-A applies
• Fabrication heat treatment: PWHT temperature, hold time and number of cycles, for simulated PWHT of test coupons
• Toughness and chemistry: Charpy temperature and energy, step cooling, J-factor and X-bar limits
• Testing and documents: ultrasonic examination; EN 10204 3.1 or 3.2 certificates and any third-party inspection (see our guide to material test certificates)
• Matching items: heads, nozzles, forgings and consumables of compatible grades; for formed heads, see pressure vessel heads

Common Mistakes

1. Ordering the grade without the class. "SA-387 22" describes two plates whose minimum tensile strengths differ by 100 MPa.

   Prevention: State grade and class, and the type for Grade 91.

2. Assuming Class 2 always saves thickness. In the creep range, the allowable stresses of the two classes converge.

   Prevention: Compare code allowable stresses at the design temperature.

3. Buying plate before the PWHT is known. A PWHT hotter or longer than the mill allowed for can leave the plate below its specified strength.

   Prevention: Give the mill the full PWHT cycle, including repairs, and order simulated-PWHT coupons.

4. Treating 12Cr1MoVR as a drop-in for SA-387 Grade 11 or 22. Composition, standard and allowable stresses differ.

   Prevention: Check that the design code accepts the grade, and qualify the welding procedure on it.

5. Leaving impurity limits out of a hydrogen-service order. Plate and weld metal may then carry enough impurities to embrittle in service.

   Prevention: Put J-factor, X-bar and step-cooling requirements in the enquiry.

6. Designing to the Nelson curve with no margin. HTHA has occurred below the curves.

   Prevention: Apply a margin on temperature and hydrogen partial pressure, and use the current edition of API RP 941.

7. Pressurising a cold reactor. A temper-embrittled shell can fracture at low temperature under pressure.

   Prevention: Respect the minimum pressurisation temperature at every start-up and shutdown.

Supply from Kasko Makine

Kasko Makine supplies Cr-Mo and Cr-Mo-V alloy steel plate:

• SA-387M Gr22 Cl2 steel plates — hot-rolled chromium-molybdenum alloy steel plates to ASTM / ASME SA-387M Grade 22 Class 2, for high-temperature and high-pressure applications: pressure vessels and boilers, heat exchangers, petrochemical and refinery equipment, tubes, piping and high-temperature machinery parts
• 12Cr1MoVR steel plates — hot-rolled alloy steel plates to GB/T 713 12Cr1MoVR, for boilers and pressure vessels, heat exchangers, petrochemical and refinery equipment, power generation systems and high-temperature machinery components
• Steel plates — the plate range, in various thicknesses, widths and grades, which also lists SA-240M 304, 304H and 310S, SA-479M 309 and SA-351M CK20; see our guide to heat-resistant stainless steel

Engineering support: Send the design code, design temperature and pressure, hydrogen partial pressure, PWHT cycle and plate list. We will review grade, class and test requirements against your data and reply with pricing, lead time and engineering details.

Send the grade, class, thickness, plate size, quantity and PWHT cycle for a quotation — we reply within 24 hours. Reach us at info@kaskomakine.com or WhatsApp +90 (537) 521 1399.

Continue Reading

• Alloy Steel Pipe (ASTM A335): Chrome-Moly Grades P11, P22, P91 Explained
• ASTM A213 Alloy Tubes: T11, T22 and T91
• Carbon Steel Plate: ASTM A516 and A36 Grades and Specifications
• Heat-Resistant Stainless Steel: 304H, 309S and 310S
• Weld Overlay and Clad Construction: CRA Cladding, Dilution and Qualification

Frequently Asked Questions

Q: What is SA-387 steel plate?
A: SA-387 is the ASME version of ASTM A387, the specification for chromium-molybdenum alloy steel plate intended mainly for welded boilers and pressure vessels in elevated-temperature service. Grades are named by alloy content: Grade 11 is 1.25Cr-0.5Mo, Grade 22 is 2.25Cr-1Mo, Grade 5 is 5Cr-0.5Mo and Grade 91 is 9Cr-1Mo with vanadium and niobium. Plates are annealed (Class 1 only), normalised and tempered, or accelerated-cooled and tempered.

Q: What is the difference between SA-387 Class 1 and Class 2?
A: The class sets the strength level of the same chemistry. For Grade 22, Class 1 requires a tensile strength of 415 to 585 MPa and a minimum yield of 205 MPa, while Class 2 requires 515 to 690 MPa and 310 MPa. Class 2 allows thinner walls where short-term strength sets the allowable stress, but in the creep range the advantage largely disappears.

Q: What is SA-387 Grade 22 Class 2 used for?
A: SA-387 Grade 22 is 2.25Cr-1Mo steel plate, and Class 2 is its higher-strength level, with 515 to 690 MPa tensile and 310 MPa minimum yield. It is used for pressure vessels, boilers, heat exchangers and refinery equipment that run hot, including reactors in hydrogen service, where it is often ordered with impurity limits, step-cooling tests and simulated post-weld heat treatment of the test coupons.

Q: What is 12Cr1MoVR steel?
A: 12Cr1MoVR is a Chinese boiler and pressure-vessel plate grade under GB/T 713, with about 0.08 to 0.15 percent carbon, 0.90 to 1.20 percent chromium, 0.25 to 0.35 percent molybdenum and 0.15 to 0.30 percent vanadium. It is the plate version of 12Cr1MoV, a creep-resisting steel with a long record in power plant steam lines. The tube version, 12Cr1MoVG, is made under GB/T 5310.

Q: Is 12Cr1MoVR equivalent to SA-387 Grade 11 or Grade 22?
A: No. 12Cr1MoVR is approximately comparable to the 1 to 1.25 percent chromium grades in room-temperature strength, but it contains vanadium and less molybdenum, and Grade 22 has about twice its chromium. Its closest relative is the Russian 12Kh1MF; the Chinese counterparts of Grades 11 and 22 are 14Cr1MoR and 12Cr2Mo1R. Substituting it needs a design code that lists the grade with allowable stresses, and a welding procedure qualified on the actual steel.

Q: What is temper embrittlement and how is it controlled?
A: Temper embrittlement is a loss of toughness in steels such as 2.25Cr-1Mo after long exposure at roughly 400 to 600 degrees Celsius, caused by antimony, phosphorus, tin and arsenic segregating to grain boundaries. It is controlled with clean steel: J-factor limits for plate and weld metal, X-bar limits for weld metal, and step-cooling tests that compare Charpy transition temperatures before and after an accelerated embrittling treatment.

Q: What preheat and PWHT does SA-387 Grade 22 need?
A: Typical practice for 2.25Cr-1Mo, as published by TWI, is a minimum preheat of 150 degrees Celsius up to 15 mm and 200 degrees Celsius above, a maximum interpass temperature of 350 degrees Celsius, low-hydrogen consumables and PWHT at about 680 to 720 degrees Celsius. ASME Section VIII Division 1 sets a minimum holding temperature of 677 degrees Celsius. Keep PWHT below the plate's tempering temperature.