Welding of P11 material, P11 to carbon steel Complete Guide

What is P11 Material?

P11 material 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 plants, oil & gas fields for the fabrication of pressure vessels, columns, and pipelines as per ASME Section IX, Section 1 and B31.3, etc.

Chromium (Cr) as an alloying element in this steel, provides elevated-temperature strength, improved oxidation resistance at high temperatures, and increases the tensile strength, yield strength & material hardness.

Molybdenum (Mo) in P11 material rises the load-bearing capacity, Yield strength, hardness, and toughness properties.

The Steel alloy contains 1.25% chromium and 0.5% Molybdenum thus the name is 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 is WC6.

  • B11: Bar
  • F11: Forging
  • T11: Seamless tube
  • WC6: Casting
  • P11: Pipe

P11 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, the material is A387 as shown in the below table.

P11 Material Specification
Specification Material Form Grade
 ASTM A335  Pipes  P11
  ASTM A213  Tubes  T11
  ASTM A234  Fittings  W11
  ASTM A182  Forging  F11
  ASTM A217  Casting  WC6
  ASTM A387  Plate  Grade 11

Chemical and mechanical properties of P11 material

The chemical and mechanical properties of P11 material are important to consider when selecting a material for a specific application.

Detailed chemical & mechanical properties of most widely used ASTM A335 P11 (SA335 P11 chemical composition) material are given in the below table:

P11 Material chemical composition
Element % Composition
 Carbon 0.05- 0.15
  Chromium  1.0- 1.50
 Molybdenum  0.44- 0.65
Manganese 0.30- 0.60
 Silicon  0.50- 1.0
Sulfur 0.025 Max
 Phosphorus  0.025 Max
P11 material properties

Welding P11 Material

P11 Material or 1.25Cr-0.5Mo is known for its high strength and resistance to wear at high temperature applications. The welded joint of P11 material need to be as strong as the base metal and same resistance to oxidation.

In order to achieve a weld that is strong with optimum properties, the following steps should be followed:

  1. The pieces of metal to be welded should be cleaned and free of any contaminants.
  2. The welding area should be prepped by using a wire brush or grinder to remove any paint or rust.
  3. A welding rod that matches the composition of the base metal should be selected.
  4. The welding process should be performed using a steady hand and proper technique.
  5. The welded joint should be allowed to cool slowly in order to avoid cracking.

P11 Welding Electrode

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.

The E8018-B2 welding electrode is a versatile, low-alloy electrode that can be used for welding a variety of metals. It produces high-quality welds with low levels of spatter, making it an ideal choice for use in a variety of applications.

Additionally, the E8018-B2 electrode is available in a number of different sizes, making it easy to find the perfect fit for your needs.

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.

P11 welding filler wire

P11 welding filler wire are ER80S-B3, ER90S-B3 and E9XT1-B3C. ER80S-B3 and ER90S-B3 are TIG & MIG welding filler wires used for welding of P11 material to itself, P11 to P22 and P11 to Carbon steel welding.

E9XT1-B3C is low alloy wire used for welding of P11 material by Flux Cored arc welding (FCAW).

Gas shielding is required for welding of ER80S-B3, ER90S-B3 and E9XT1-B3C. Pure argon is used for tig welding while argon-CO2 mix is used with MIG welding.

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 the below table.

E8018 B2 properties 2 Welding of P11 material, P11 to carbon steel Complete Guide

Preheating and interpass temperature for P11 Welding

Welding preheat for Cr-Mo steel is important to achieve the desired properties in the welded joint.

The temperature of the weldment must be raised above the minimum required preheat temperature for the base metal, and maintained at that temperature until the welding process is complete.

Preheating can be accomplished by heating the welding joint & surrounding area. Preheat control shall be placed in to ensure application of right preheat temperature.

Welders have long been familiar with the need for preheat when welding carbon steel. The addition of chromium and molybdenum to the alloy changes the behavior of the steel, making it more prone to cracking.

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.

Try our Online Welding Preheat Calculator for Free.

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

PWHT requirement for P11 material

PWHT for P11 or common Cr-Mo steel is a process that is often used to help improve the mechanical properties of the steel.

The process helps to relieve residual stress, and can also help to improve the microstructure of the steel.

The PWHT process can be performed in a variety of ways, including through local PWHT or full PWHT in furnace, or even using induction heating.

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 at 1 h/25 mm (1 hr/in.) and 15 minimum (Ref: API 582).

PWHT for Cr-Mo steel is a critical step in the manufacturing process to ensure the steel’s properties are met. The steel must be heated to a certain temperature and then cooled slowly.

This process helps to prevent any micro-cracks from forming in the steel & reduces the residual stresses, which could lead to failure down the road.

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 E8018-B3 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.

P11 to P22 welding electrode

Read more: P22 Material Welding Guide

P11 to P22 welding electrodes are:

  • E8018-B3, E8015-B3, E8016-B3, E9018-B3 (For stick welding applications)
  • ER80S-B3, ER90S-B3 (For TIG & MIG Welding),
  • E9XT1-B3C (For flux cored arc welding)

P11 to P22 welding electrodes are classified in AWS A5.5 for stick welding, AWS A5.28 for TIG & MIG Welding and AWS A5.29 for flux cored arc welding.

Difference between P11 and P22 material

Both P11 and P22 material are Chrome-Moly alloy materials used for high temperature (elevated) service. Although, both has differences in chemistry and other properties as listed below:

  • P11 contains 1.25%Cr-0.5%Mo, while P22 contains 2.25%Cr-1%Mo.
  • Both materials has same mechanical strength.
  • P11 service temperature limit is less compared to P22 material.
  • P22 material has higher hardness compare to P11 material.
  • P22 creep strength is higher than P11 material.

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