A335 P22 Alloy Steel Pipe for Higher-Temperature Lines

At room temperature, very little. Both grades share the same minimum tensile and yield values in ASTM A335. The difference is how the steel behaves after years at high temperature. With about 2¼% chromium and 1% molybdenum, P22 has higher creep-rupture strength and better oxidation resistance, so design codes give it more allowable stress in the hot range.

There is a small chemistry trap too. P11 requires silicon of 0.50–1.00%, while P22 simply caps silicon at 0.50%. So a certificate with low silicon is normal for P22 but would be wrong for P11.

Like P11, P22 pipe is supplied full annealed, isothermal annealed, or normalised and tempered. The normalise-and-temper route needs a minimum tempering temperature of 675 °C (1250 °F), 25 °C higher than for P11. Your certificate should state the heat treatment condition and temperatures; if it does not, ask for them before the pipe is fabricated. Pipe that has been re-heat-treated after supply, for example after hot bending, needs its own record of the new cycle.

Most problems with alloy pipe orders come from missing details, not bad steel. Work through this list before sending your enquiry to us:

• Confirm the grade on the isometric and in the line list match; P22 lines often sit next to P11 lines
• Give NPS and schedule, or OD and wall, following ASME B36.10 sizes
• State IBR if the line is a steam pipe under the boiler law; the certificate route must be fixed before manufacture
• Ask for matching WP22 butt-weld or F22 forged fittings from the same order
• Specify any extra tests your client needs, such as positive material identification or third-party witness

P22 is produced in smaller volumes than P11 and carbon steel pipe, so less common sizes and heavy schedules can take longer to locate. Plan the alloy pipe early in a shutdown schedule, and order a small allowance for cut-outs and weld coupons, because a short length cannot always be borrowed from another job.

When the line is IBR, the certificate route adds time too: the maker or Inspecting Authority has to be involved from the start, not at dispatch. We confirm sizes, schedules and documentation at the time of enquiry, and say clearly if a size has to be sourced specially rather than drawn from stock.

P22 welds harden more readily than P11, so preheat, interpass control and post-weld heat treatment are standard practice and usually mandatory under ASME B31.1 and B31.3 above small thicknesses. The matching filler family is B3, for example E9018-B3 electrodes or ER90S-B3 wire.

Hardness checks after PWHT are a common client requirement on P22 joints. Plan for them in the inspection test plan rather than discovering them at handover. Our fittings range includes alloy steel butt-weld and forged fittings to go with P22 pipe.

Power stations are the classic home for P22, especially main steam and hot reheat lines and the headers that collect steam from superheater tubes. Refineries and petrochemical plants use it for heater outlet piping and hot hydrocarbon service. In South India, P22 is also found in the high-pressure steam systems of larger sugar mill cogeneration plants and in captive power and IBR boiler installations.