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Pressure Vessel and Chromium-Molybdenum Steel

Pressure vessel and heat-resistant steels are code materials — plate, pipe and forgings certified to ASME, EN 10028 or GB 713 with guaranteed toughness at the minimum design temperature and, in the Cr-Mo grades, creep strength at the maximum. Carbon-manganese grades (A516 Gr 70, P265GH, Q345R, about 260–355 MPa yield) serve to roughly 400 °C; 1¼ and 2¼ % chromium-molybdenum (A387 Gr 11 and A387 Gr 22, 15CrMo, A335 P22) extend that to about 540–580 °C; and 9 % Cr P91 / P92 run steam lines and headers at 600–620 °C. They are fully killed, fine-grained and usually normalized so they stay tough after welding.

Popular pressure vessel steel grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
A516 Gr 703205507.85GoodExcellentDefault vessel and exchanger plate to about 400 °C
P265GH2954657.85GoodExcellentEN carbon plate for boilers and vessels
Q345R3705507.85GoodExcellentGB pressure vessel plate, 345 MPa yield
A387 Gr 223855707.85FairGood2¼ Cr-1 Mo plate for hot and hydrogen service
A335 P223505507.85FairFair2¼ Cr-1 Mo seamless pipe to about 580 °C
P917501,0007.77PoorPoor9 % Cr steam piping and headers to 600 °C
15CrMo3055007.85FairGoodGB 1 Cr-½ Mo boiler tube and forgings

All 181 pressure vessel steel grades

Choose pressure vessel steel for

Boilers, drums, headers, steam and process piping, heat-exchanger shells, reactors, air receivers, storage spheres and any pressure-retaining part built to a design code — where certified toughness, creep data and weld-procedure qualification matter more than machinability.

Look elsewhere when

The part is not pressure-retaining and simply needs strength (A36 or S355J2 structural plate is cheaper and machines the same), the service is corrosive rather than hot (316L or duplex 2205 stainless), the temperature exceeds about 620 °C or the atmosphere oxidizes hard (heat-resisting 310S, 253 MA or Inconel 625), or a machined component needs hardness — none of these grades is hardened.

Yield strength against elongation at break, Pressure vessel & Cr-Mo heat-resistant among every steel grade

No materials in view have both of these properties.

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Pressure vessel steel by application

Vessels and exchangers to 400 °C
A516 Gr 70, P355GH or Q345R plate with A106 Grade B nozzles, normalized when the code requires it for thickness or impact testing. A285 and A516 Gr 60 for thin, heavily formed shells.
Hot piping and headers
A335 P11 and 15CrMo to about 540 °C, A335 P22 and 12Cr1MoV to about 580 °C, P91 / P92 above that. Match the filler (ER80S-B2, ER90S-B3, ER90S-B9) and follow the code preheat and post-weld heat treatment.
Hydrogen and refinery reactors
A387 Gr 22 and A387 Gr 22L Class 1 heavy plate (2¼ Cr-1 Mo) resists hydrogen attack within the Nelson-curve limits; vanadium-modified ASTM A182 F22V forgings for the heaviest walls.
Cryogenic and low-temperature service
P355NL2 and P460NL2 fine-grain plate to about −50 °C, A203 nickel steel below that, and 9 % nickel X8Ni9 for LNG at −196 °C.

Working with pressure vessel steel

Machining
Carbon and 1¼–2¼ Cr-Mo grades machine like normalized 1020 to 4130 — soft (150–200 HBW), a little gummy on drilling, easy to cut. P91 is delivered normalized and tempered at about 200–250 HBW and machines like tempered 4140. Nozzle bores, flange faces and tube-sheet holes are the only machining most vessels see.
Welding
Carbon grades weld with ER70S-6 / E7018, preheated above about 25–32 mm. Cr-Mo grades need matching filler, preheat (about 150 °C for P11 / P22, 200–250 °C for P91) and post-weld heat treatment — 690–720 °C for P22, 750–770 °C for P91 — inside a tight window, because an over- or under-tempered P91 weld loses its creep strength. Every joint is procedure-qualified and the vessel hydrotested.
Forming
Plate is cold-rolled into shells at about 3 t and above; heads are hot- or cold-pressed and then normalized when the cold strain exceeds about 5 %. Cr-Mo and 9 % Ni grades are formed hot and always re-heat-treated. Dished heads, tube bends and induction bends come from specialist forming shops.
Heat treatment
These steels are supplied normalized (or normalized and tempered) and used that way — the only shop heat treatment is post-weld stress relief at 600–770 °C depending on grade. Never quench-harden them; hardness above about 225–248 HBW in a weld or heat-affected zone is a rejection criterion in sour service and most codes.

Other steel series

Pressure Vessel and Chromium-Molybdenum Steel — frequently asked

What is pressure vessel steel?

Pressure vessel and heat-resistant steels are code materials — plate, pipe and forgings certified to ASME, EN 10028 or GB 713 with guaranteed toughness at the minimum design temperature and, in the Cr-Mo grades, creep strength at the maximum. Carbon-manganese grades (A516 Gr 70, P265GH, Q345R, about 260–355 MPa yield) serve to roughly 400 °C; 1¼ and 2¼ % chromium-molybdenum (A387 Gr 11 and A387 Gr 22, 15CrMo, A335 P22) extend that to about 540–580 °C; and 9 % Cr P91 / P92 run steam lines and headers at 600–620 °C. They are fully killed, fine-grained and usually normalized so they stay tough after welding.

Which grade of pressure vessel steel should I use?

A516 Gr 70 (P355GH on EN drawings, Q345R on GB) is the default plate for ambient- and moderate-temperature vessels, heat exchangers and air receivers; A516 Gr 60 or P265GH where more forming or a thinner shell matters. Seamless carbon-steel pipe is A106 Grade B or P235GH. Move to A387 Gr 11 / A335 P11 (1¼ Cr-½ Mo) or 15CrMo at about 450–540 °C, and to A387 Gr 22 / A335 P22 (2¼ Cr-1 Mo) for hydrogen service and heavy-wall reactors; 12Cr1MoV is the GB boiler-tube grade in the same range. P91 (A335 P91, A387 Gr 91 Cl 2) is the answer for main steam piping and headers at 570–600 °C, with P92 for the highest ultra-supercritical temperatures. Below about −50 °C the nickel steels take over: A203 to about −100 °C and 9 % nickel X8Ni9 for LNG at −196 °C.

Which grade of pressure vessel steel is the strongest?

52CrMoV4 has the highest yield strength in the series at 1,050 MPa; A372 Grade L follows at 1,030 MPa. Values are for each grade's default condition.

Which grade of pressure vessel steel is easiest to machine?

A285 (machinability good, 68/100), then P265GH (66/100).

Is pressure vessel steel heat-treatable?

Some grades are. Check the conditions listed on each grade page.

A516 Gr 60 or Gr 70?

Same steel family, different strength: Gr 70 gives 260 MPa minimum yield and 485–620 MPa tensile against 220 MPa and 415–550 MPa for Gr 60, so it lets the shell be about 15 % thinner for the same pressure. Gr 60 has lower carbon, forms tighter and needs less preheat, which is why it is chosen for thin, heavily formed heads and for low-temperature toughness. Most fabricators keep Gr 70 as their default plate.

P22 or P91 for a steam line?

P22 (2¼ Cr-1 Mo) is the economical choice to about 565–580 °C and forgives a lot in welding and heat treatment. P91 (9 Cr-1 Mo-V-Nb) has roughly twice the allowable stress at 600 °C, so the pipe wall can be about half as thick, but every weld needs controlled preheat, 750–770 °C post-weld heat treatment and strict filler control, and it is unforgiving of poor tempering and of Type IV cracking in the fine-grained heat-affected zone under long-term creep. Use P91 when the design temperature exceeds what P22 can carry, or when wall thickness and thermal fatigue in thick P22 become the problem.