ASTM A335 P22 – also written ASME SA335 Grade P22, UNS K21590 – is a 2.25 percent chromium, 1 percent molybdenum ferritic alloy steel pipe for high-temperature service. It has a minimum yield strength of 205 MPa and a minimum tensile strength of 415 MPa in the normalized and tempered condition, and it remains one of the most widely specified chrome-molybdenum grades for steam and process piping in the 540 to 565 degrees Celsius range.
Download ASTM A335 P22 Pipe data sheet (PDF) One-page summary of the supply range, chemistry, mechanical properties and inspection documents on this page. The standard is the governing document.
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Size range and specification
- Outside diameter 1/2 inch – 36 inch (12.7 – 914 mm)
- Wall thickness SCH 40 – SCH XXS, or by wall thickness
- Length SRL 5.8 m, DRL 11.8 m, or fixed length
- Ends Plain end, beveled end
- Surface treatment Black varnish, bare, rust preventive oil
- Manufacturing process Hot finished seamless
- Heat treatment Normalized and tempered
- Delivery standard ASTM A335 / ASME SA335, dimensions to ASME B36.10M
- Delivery condition Normalized and tempered
How this grade is supplied
- Inspection Inspected by the producing mill’s own inspection department, which is independent of production, against the delivery standard above. Third-party inspection — SGS, BV or TUV, or an inspector you send yourself — can be arranged at the mill or before shipment; give us the dates and the scope at the order stage.
- Certificate A mill test certificate to EN 10204 3.1 showing the heat number, the chemical composition and the mechanical results is standard on every order. EN 10204 3.2, countersigned by the inspector you nominate, is available on request.
- Documents with the goods The mill test certificate and the packing list travel with the shipment, and the heat number is traceable from cast through to the finished product.
- Packing Sea-worthy export packing: bundled by size with end protection, corrosion protection on request, stencilled with the size, grade and heat number.
- MOQ One bundle or one truckload; mixed sizes within a bundle accepted.
- Lead time Counted from order confirmation, not from the enquiry. Stock sizes 5–10 days; mill run or non-stock 3–5 weeks. The delivery window is fixed on the quotation.
- How we supply Sourced through partner mills; the producing mill is named on the quotation.
ASTM A335 P22 chemical composition (%)
| Element | Range | Element | Range |
|---|---|---|---|
| Carbon, C | 0.05 – 0.15 | Nickel, Ni | 0.50 max |
| Manganese, Mn | 0.30 – 0.60 | Chromium, Cr | 1.90 – 2.60 |
| Phosphorus, P | 0.025 max | Molybdenum, Mo | 0.87 – 1.13 |
| Sulphur, S | 0.025 max | ||
| Silicon, Si | 0.50 max |
The chromium and molybdenum ranges are what give P22 its elevated-temperature strength and its oxidation resistance; the low carbon range keeps the steel weldable and tough, and phosphorus and sulphur are held down because both reduce creep ductility. The nickel limit is a residual control rather than an alloy addition. Some published tables give a slightly narrower carbon range or a wider silicon range than shown here, so the mill certificate should be read against the edition of A335 the order names.
Source: chemical composition requirements of ASTM A335 / ASME SA335, Table 1. The standard is the governing document.
ASTM A335 P22 mechanical properties (normalized and tempered)
| Grade | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| P22 (ASTM A335) | 415 MPa min (60,000 psi) | 205 MPa min (30,000 psi) | 30% min | 163 HBW max |
Values are the room-temperature requirements of ASTM A335 for Grade P22 in the normalized and tempered condition. The stresses used to size a hot line are the elevated-temperature allowable stresses tabulated in ASME B31.1 and in the ASME Boiler and Pressure Vessel Code, not the room-temperature values above, and they fall as the temperature rises. Published hardness limits for P22 vary between sources; the figure shown is the one quoted most consistently.
Source: tensile requirements of ASTM A335 / ASME SA335, Table 1. The standard is the governing document.
What Is ASTM A335 P22 Pipe?
ASTM A335 P22 – ASME SA335 Grade P22, UNS K21590 – is a seamless ferritic alloy steel pipe for high-temperature service, with 1.90 to 2.60 percent chromium and 0.87 to 1.13 percent molybdenum and a minimum yield strength of 205 MPa. Along with A106 Grade B it is one of the two grades that most hot process and steam piping is ordered in, and it is the pipe grade that matches A182 F22 forgings and A234 WP22 fittings, so a P22 line can be built from flanges, fittings and pipe that all sit in the same chrome-molybdenum family.
Why 2.25Cr-1Mo Became the Workhorse Grade
The chromium in P22 forms a protective oxide that slows scaling and keeps the steel from being attacked by steam at high temperature, and the molybdenum raises the temperature at which the steel starts to creep. The combination is what makes P22 usable at temperatures where plain carbon pipe such as A106 Grade B is no longer acceptable, and it does so at a cost well below the 9 percent chromium grades. That balance – enough alloy to hold up at temperature, not so much that the steel becomes difficult to weld and expensive to buy – is why the 2.25Cr-1Mo composition has stayed in specification for so long and appears in almost every refinery and power plant built in the last fifty years.
P22 versus P11 and P91
P11 carries about 1.25 percent chromium and 0.50 percent molybdenum and sits below P22 in high-temperature strength; it is specified where the operating temperature is lower and the cost of the extra chromium is not justified. P22 is the middle step, and P91 – the 9Cr-1Mo-V grade – is far above both: its creep strength at 550 to 600 degrees Celsius allows a much thinner wall, which is why newer high-pressure steam lines are built in P91 rather than P22. Moving up the ladder buys allowable stress at temperature and pays for it in material cost and in the tightness of the heat treatment and welding control the higher grade demands.
Where P22 Pipe Is Used
P22 is used in power plants and in process plants: main steam and hot reheat piping at moderate superheat, steam headers and manifolds, boiler and heat recovery steam generator piping, refinery process lines in hydrotreating and hydrocracking service, and high-temperature heat exchanger and furnace piping. It is also common in high-pressure steam distribution headers where carbon steel has run out of allowable stress but the design temperature has not reached the point where the 9 percent chromium grades are needed.
Heat Treatment, Welding and Documentation
P22 is supplied normalized and tempered, and the heat treatment is recorded on the mill certificate because the tempering temperature controls the balance of strength and toughness. The grade is welded routinely, but it is not welded like carbon steel: preheat and interpass temperature are controlled, the filler metal must match the chrome-molybdenum composition, and post-weld heat treatment is required on most wall thicknesses to restore the heat-affected zone. Because P22 is a creep-grade steel, the mill certificate, the heat treatment record and the hardness results on the completed welds form part of the delivered documentation.
Typical applications
- Main steam and hot reheat piping at moderate superheat
- Steam headers and manifolds
- Boiler and heat recovery steam generator piping
- Refinery hydrotreating and hydrocracking process lines
- High-temperature heat exchanger and furnace piping
Standards covered
What to state on the enquiry
- ASTM A335 P22, supplied normalized and tempered.
- Size and schedule, or outside diameter and wall.
- Quantity and destination port.
- Certificate type and any inspection requirements.
Frequently asked questions
What is the difference between P11, P22 and P91?
They are the three steps of the chrome-molybdenum ladder used for hot piping. P11 has about 1.25 percent chromium, P22 has about 2.25 percent chromium and 1 percent molybdenum, and P91 has 9 percent chromium with vanadium and niobium additions. Each step up increases the allowable stress at elevated temperature and therefore allows a thinner wall, and each step up also increases the material cost and the control needed in heat treatment and welding.
What is the maximum service temperature for P22 pipe?
There is no single number. The limit is set by the allowable stress the design code tabulates for the grade at the design temperature, so it depends on the code and on the wall thickness, and published guidance for P22 generally falls in the 540 to 565 degrees Celsius band. Above that range the allowable stress drops far enough that a designer normally moves to a 9 percent chromium grade such as P91. The design temperature and the applicable code, not the pipe, decide the answer.
What is the difference between P22 and F22?
They are the same alloy in two product forms. P22 is the seamless pipe grade under ASTM A335, and F22 is the forged grade under ASTM A182; the two are used together on the same line so that pipe, flanges and valve bodies share one composition and one allowable stress basis. A234 WP22 is the matching wrought fitting grade.
Where to go next
- ASTM A335 Alloy Steel Pipe – alloy steel pipe for high-temperature service
- ASTM A335 P91 Pipe – 9Cr-1Mo-V pipe for main steam and reheat lines
- Alloy Steel Fittings – alloy fittings for high-temperature service
- Boiler & Heat Exchanger – tube and pipe for boilers and heat exchangers
- Pipe Schedule Chart – wall thickness for every schedule
- Steel Pipe Standards & Grades – every grade page in this section
- Get a Quote – send the grade, size, quantity and destination port
- Boiler & Heat Exchanger Tube – tube specified by outside diameter and wall
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