Welding of P11 material, P11 to carbon steel


What is P11 Material?

P11 or T11 or F11 or ASTM A387 Gr. 11, also known as 1.25Cr-0.5 Mo (UNS No.: K11597) is a high temperature low alloy steel material used mainly in power plant, oil & gas field for the fabrication of pressure vessels, columns, and pipelines as per ASME Section IX, Section 1 and B31.3 etc. Chromium (Cr) provides high-temperature strength, improved oxidation resistance at high temperature and increase the tensile strength, yield strength & hardness at room temperatures. Molybdenum (Mo) in P11 material rises the strength, elastic limit, resistance to wear, toughness properties & hardenability. Molybdenum is very important for increasing high temperature creep strength, or creep resistance in the materials as well as improves the corrosion resistance of the material.

The Steel alloy contains 1.25% chromium and 0.5% Molybdenum thus the name given as 1 1/4Cr-1/2Mo. If the material is supplied in pipe form it is designated as P11, in forging it is called F11, wrought fitting is W11 and casting as WC6.

Material Specification

P11 material specification is A335 for pipe, A213 for Tube, A234 for wrought fitting, for forging A182, For casting A217 and for plate material is A387 as shown in below table.

Chemical and mechanical properties of P11 material

Welding electrode for P11 Material

SMAW or stick welding of P11 material is carried out using E8018-B2 (Low alloy low hydrogen electrodes). E8018-B2 gives the weld deposit as the base metal and matching base metal properties. TIG or MIG welding is carried out using ER80S-B2 filler wire. The SMAW electrodes need to be baked before the welding. Click below for baking requirements.

What is Low Hydrogen electrodes, Their Storage & Baking Procedure?

The typical minimum weld metal deposit chemistry and mechanical properties of E8018-B2 are given in below table.

Preheating and interpass temperature for P11 Welding

Preheating and interpass temperature for P11 Welding is very critical as the weld metal is air hardenable. If proper preheating is not applied, the weld will be hardened and can get hydrogen cracking. The minimum preheat temperature of 250 °F (120 °C) shall be applied during the welding.

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The interpass temperature is kept maximum 600 °F (315 °C) for P11 material welding.

Post heating or PWHT

Post heating or PWHT of P11 welding is carried out at 650 °C to 705 °C (1,200 °F to 1,300 °F). The holding time is kept 1 h/25 mm (1 hr/in.) and 15 minimum.

Welding P11 to Carbon Steel

Welding of P11 to Carbon Steel can be carried out using SMAW or stick welding with E7018 or E8018-B2. E8018-B2 is recommended to provide better weldment properties compare to E7018. TIG or MIG welding of P11 is carried out using ER70S-6 or ER80S-B2 filler wire.

Welding P11 to P22 and P91

Welding of P11 to P22 can be carried out using SMAW or stick welding with E8018B3 or E8018-B2. E8018-B3 is recommended.. TIG or MIG welding of P11 is carried out using ER90S-B3 or ER80S-B2 filler wire.

P11 to P91 welding is carried out using E8018-B8 or ER80S-B8 filler wire.

Welding of P91 material and electrode/ TIG-MIG filler for P91

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