ASTM A335 P11 Alloy Steel Seamless Pipes

ASTM A335 P11 Chrome Moly Seamless Pipe (1.25Cr-0.5Mo)

ASME SA335 Grade P11 alloy steel pipe for boiler headers, economisers and IP steam service

Savoy Piping Inc. supplies ASTM A335 P11 / ASME SA335 Grade P11 seamless chrome moly pipe — the familiar 1.25Cr-0.5Mo grade (UNS K11597) that still underpins a large share of thermal power and process steam piping in India and export markets.

When engineers say “P11 header stock,” they usually mean intermediate-temperature steam service: economiser connections, IP piping, HRSG headers, and boiler manifolds where carbon steel runs out of strength and oxidation resistance, but full 2.25Cr or 9Cr material is not yet required. That is exactly where P11 earns its place.

What buyers check first: schedule and heavy-wall availability, normalised-and-tempered condition, hardness limits, hydrostatic / NDE status, and — for Indian boiler jobs — whether SA335 P11 can be released with IBR Form III-C. We support those documentation needs along with EN 10204 3.1 / 3.2 MTCs.

Related grades we stock and source with P11 include P5, P9, P22, P91, P92, and tube grade ASTM A213 T11.

Also see: Alloy steel seamless hub · Chrome moly hub · Alloy buttweld.

ASTM A335 P11 Alloy Steel Seamless Pipe Range

What is ASTM A335 P11 pipe?

ASTM A335 / ASME SA335 Grade P11 is seamless ferritic alloy-steel pipe for high-temperature service. Composition is approximately 1.25% chromium and 0.5% molybdenum. It is one of the most widely procured chrome moly pipe grades for power generation and process plants because it balances elevated-temperature strength, weldability, and cost.

Pipe to this specification is intended for bending, flanging, similar forming, and fusion welding. In practice, P11 is often used where continuous metal temperatures are typically in the mid-hundreds of °C range for headers and IP steam — always confirm against the applicable ASME B31.1 / B31.3 allowable stresses and project specifications.

Chromium helps oxidation resistance at temperature; molybdenum improves creep strength and hardenability. Compared with carbon steel (for example A106), P11 holds strength and scale resistance longer in hot steam service. Compared with P22, P11 is easier to weld and is preferred for many lower-to-intermediate temperature headers.

Typical applications of ASTM A335 P11 pipe

• Boiler headers and manifolds — HP/IP header stub connections and thick-wall manifolds in subcritical plants
• Economiser piping — inlet/outlet headers and connecting lines in coal-fired and HRSG boilers
• Intermediate-pressure steam lines — extraction / bleed steam piping in the 400–540°C class (project-dependent)
• HRSG evaporator and low-temperature superheater headers
• Process plant elevated-temperature piping — refinery and chemical units when 1.25Cr-0.5Mo is classed

P11 vs P22 — which grade for steam service?

P11 (1.25Cr-0.5Mo) is the everyday chrome moly choice for many headers, economisers, and IP steam lines. P22 (2.25Cr-1Mo) provides higher chromium and better creep/oxidation performance as temperatures climb, so it is often preferred for hotter main steam and hot reheat duties. If the unit is supercritical and creep-critical, designers move to P91 or P92. Matching tube grade: A213 T11.

ASTM A335 P11 Alloy Steel Seamless Pipes chemical compositions

Heat-analysis composition limits for seamless pipe ordered as Grade P11 (UNS K11597). Values below are mass percent; confirm against the ASTM A335 / ASME SA-335 edition on the purchase order.

ASTM A335 P11 Alloy Steel Seamless Pipes tensile test

ASTM A335 P11 pipes other mechanical test

ASTM A335 P11 Seamless Pipes heat treatment

ASTM A335 P11 Seamless Pipes Permissible Variation in Wall Thickness

ASTM A335 P11 Alloy Steel pipes elongation requirement

ASTM A335 P11 pipes Permissible Variations in Outside Diameter

Outside Diameter at any point shall not vary from standard specified more than:

ASTM A335 P11 Seamless Pipes Required Markings on Each Length

(On Tags attached to each Bundle in case of Bundled Pipe) Markings will adhere to prescribed specifications in A 999/A999M and be: Rolled, Stamped, or Stenciled (Mfrs. Option)

Reference Documents for a335 P11 Alloy Steel Seamless Pipes

• ASTM A999/A 999M Specification for General requirements for Alloy and Stainless Steel Pipe.
• ASTM E 213 Practice for Ultrasonic Examination of metal Pipe and Tubing
• ASTM E 309 Practice for Eddy-Current Examination of Steel Tubular Products Using Magnetic Saturation
• ASTM E 381 Method of Macroetch testing Steel Bars, Billets, Blooms, and Forgings
• ASTM E 570 Practice for Flux Leakage Examination of Ferromagnetic Steel Tubular Products
• ASME SB26.10M Welded and Seamless Wrought Steel Pipe

a335 P11 Alloy Steel pipes Ordering Information

Orders for material under this specification should include the following, as required, to describe the desired material adequately:

Frequently asked questions — ASTM A335 P11

What is ASTM A335 P11 alloy steel pipe used for?

ASTM A335 P11 (1.25Cr-0.5Mo) seamless pipe is used for elevated-temperature boiler and process piping — headers, economiser connections, intermediate-pressure steam lines, HRSG headers, and similar Cr-Mo systems where carbon steel is not adequate.

What is the difference between P11 and P22?

P11 is roughly 1.25Cr-0.5Mo; P22 is roughly 2.25Cr-1Mo. P22 generally offers better high-temperature strength and oxidation resistance, while P11 is widely used for intermediate duties and is often considered easier to fabricate and PWHT in the field.

Do you supply IBR-certified SA335 P11 pipe?

Yes. For boiler work under Indian Boiler Regulations, we can supply ASME SA335 Grade P11 with Form III-C documentation from approved routes, in addition to EN 10204 3.1/3.2 mill test certificates.

What welding considerations apply to P11?

P11 typically requires controlled preheat, matching 1.25Cr-0.5Mo consumables (for example B2-type fillers), and mandatory PWHT per the applicable code and WPS. Always follow the approved welding procedure for wall thickness and service; do not treat P11 like carbon steel.

Export & documentation

We supply this product for domestic and export projects with mill test certificates (EN 10204 3.1 standard; 3.2 / TPI on request). Include destination, preferred Incoterms and any inspection body on the RFQ.