P number in Welding 

This article provides information about P number in welding procedure specification, welding performance qualification or any other ASME Code section that this number is used.

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P Number in welding

The P Number is addressed in I4I Academy ASME Online Training Course and ASME Section IX training Course. 

The P number in welding assigned to the material by ASME Code Section IX to reduces the number of welding procedure qualification. Why we do want to reduce the numbers of PQR’? because this part is expensive part, for each PQR you need to produce a test sample and sent to metallurgical lab for mechanical testing (two tension tests, two root bend tests and two face bend tests).

P number assigned by ASME Code Section IX to the materials based their similarity and characteristic such as chemical compositions, weldability and mechanical property. That why you do not see any material identification in the Welding Procedure Specification. What you see is the assigned P number. So your WPS can be used for group of material and not a single material.

This P number assignment reduces the number of PQR remarkably. You need one PQR for a single P number which this P number might include more than 20 or more specific materials (when impact testing is not required by construction code such as ASME Code Section VIII).

P number in Welding Application 

The assigned P Numbers to the materials addressed in the table QW-422. In addition, you can find minimum specified tensile strength, group number, UNS number, ISO 15608 Group number, nominal composition and product form.

P number is essential variable for most welding process. Similarly it is an essential variable for welding performance qualification.

The welding is not the only application of this P number assignment. This number also is used in construction code for determining Post Weld Heat Treatment degree and duration (UCS-56) also it is used to determine radiographic testing extent. The ASME Code Section VIII provided a table which obtained from combination of P number and material thickness which identifies full radiography requirements. (UCS -57)

The simple categorization of P number is:

1              Carbon Steel

3              Up to 1/2% Cr and up to 1/2% Mo

4              1 to 2% Cr and up to 1/2% Mo

5A           2 to 3% Cr, 1% Mo Alloy Steel

5B           5 to 10% Cr, 1% Mo Alloy Steel

5C           All 5A and 5B Materials heat treated to 85ksi+

6              Martensitic Stainless Steel

7              Ferritic Stainless Steel

8              Austenitic Stainless Steel

9              2 to 5% Ni Alloy Steel

10           Mn-V, Cr-V, 9%Ni, High Cr Alloy Steels

11           Low Alloy Steel, Quenched and Tempered to 95ksi+

21           1.2% Mg or Mn alloy Aluminum

22           1.2% Mn, 2,5% Mg, 0.25% Cu Aluminium

23           1.3% Mg, 0.7% Si, 0.25% Cr Aluminium

23           1.3% Mg, 0.7% Si, 0.25% Cr Aluminium

25           1.5% Mg, 0.8% Mn, 0.15% Cr Aluminium

31           Copper

32           Admiralty, Naval, Aluminium Brass, Muntz Metal

33           Cu-Si Alloys

34           Cu-Ni Alloys

41           Nickel

51           Titanium

61           Zirconium

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