Difference between “Inert” and “Active” gases

An Inert gas, such as Argon, has no effect, or reaction, on or with the welding process, it simply performs the essential task of replacing Air/Oxygen from around the weld pool. Active gases do have an effect on the welding process. The effect of an active gas on MIG Welding is twofold. Firstly, the CO2 content in an Argon/ CO2 mix makes the gas slightly electrically conductive, this in turn raises the arc voltage, which increases penetration. The second effect is the CO2 content breaks down the surface tension of the molten weld pool. Using CO2 to break the surface tension of the molten weld pool allows the weld to flow and flatten slightly for the correct weld deposit profile
If an active gas is used for TIG Welding the raised arc voltage will increase hole blows and cause excessive burning of the Tungsten Electrode.

If an Inert gas is used for MIG Welding (except Aluminum and Mig Braze), higher machine power output will be needed to achieve penetration and the finished weld will look too tall because the surface tension has not been broken.

Keep reading, Happy welding

Thank you,

KP Bhatt



ASME P Number and F Number


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ASME P Number

To reduce the number of welding and brazing procedure qualifications required base metals have been assigned P-Numbers by the ASME BPVC. Ferrous metals which have specified impact test requirements have been assigned Group Numbers within P-Numbers.

These assignments have been based on comparable base metal characteristics, such as:

  •      Composition
  •      Weldability
  •      Brazeability
  •      Mechanical Properties

Indiscriminant substitution of materials in a set of P-Numbers or Group Numbers may lead to problems or potentially failures.  Engineering assessment is necessary prior to a change in materials.

When a base metal with a UNS number Designation is assigned a P-Number, then a base metal listed in a different ASME material specification with the same UNS number shall be considered that P-Number.

The table below is a guide and is for instructive purposes only.  Anyone specifying materials or requirements should refer directly to the ASME Boiler and Pressure Vessel Code to specify materials.

P-Numbers Base Metal (Typical or Example)
1 Carbon  Manganese  Steels (four Group Numbers)
2 Not Used
3 Half Molybdenum or half Chromium, half Molybdenum (three Group Numbers)
4 One and a quarter Chromium, half Molybdenum (two Group Numbers)
5A Two and a quarter Chromium, one Molybdenum
5B Five Chromium, half Molybdenum or nine Chromium, one Molybdenum (two Group Numbers)
5C Chromium, Molybdenum, Vanadium (five Group Numbers)
6 Martensitic Stainless Steels (Grade 410, 415, 429) (six Group Numbers)
7 Ferritic Stainless Steels (Grade 409, 430)
8 Austenitic Stainless Steels

·              Group 1 – Grades 304, 316, 317, 347

·              Group 2 – Grades 309, 310

·              Group 3 – High Manganese Grades

·              Group 4 – High Molybdenum Grades

9A, B, C Two to four Nickel Steels
10A, B, C, F Various low alloy steels
10H Duplex and Super Duplex Stainless Steel (Grades 31803, 32750)
10I High Chromium Stainless Steel
10J High Chromium, Molybdenum Stainless Steel
10K High Chromium, Molybdenum, Nickel Stainless Steel
11A Various high strength low alloy steels (six Group Numbers)
11B Various high strength low alloy steels (ten Group Numbers)
12 to 20 Not Used
21 High Aluminum content (1000 and 3000 series)
22 Aluminum (5000 series – 5052, 5454)
23 Aluminum (6000 series – 6061, 6063)
24 Not Used
25 Aluminum (5000 series – 5083, 5086, 5456)
26 to 30 Not used
31 High Copper content
32 Brass
33 Copper Silicone
34 Copper Nickel
35 Copper Aluminum
36 to 40 Not Used
41 High Nickel content
42 Nickel, Copper – (Monel 500)
43 Nickel, Chromium, Iron – (Inconel)
44 Nickel, Molybdenum – (Hastelloy B2, C22, C276, X)
45 Nickel, Chromium
46 Nickel, Chromium, Silicone
47 Nickel, Chromium, Tungsten
47 to 50 Not Used
51, 52, 53 Titanium Alloys
61, 62 Zirconium Alloys


ASME F Number

The F-number grouping of electrode and welding rod in QW-432 is based essentially on their usability characteristics, which fundamentally determine the ability of welders to make satisfactory welds with a given filler metal. This grouping is made to reduce the number of welding procedure and performance qualifications, where this can logically be done. The grouping does not imply that base metals or filler metals within a group may be indiscriminately substituted for a metal which was used in the qualification test without consideration of the compatibility of the base and filler metal from the standpoint of metallurgical properties, PWHT design and service requirements, and mechanical properties.

F Number General Description
1 Heavy rutile coated iron powder electrodes :- A5.1 : E7024
2 Most Rutile consumables such as :- A5.1 : E6013
3 Cellulosic electrodes such as :- A5.1 : E6011
4 Basic coated electrodes such as : A5.1 : E7016 and E7018
5 High alloy austenitic stainless steel and duplex :- A5.4 : E316L-16
6 Any steel solid or cored wire (with flux or metal)
2X Aluminium and its alloys
3X Copper and its alloys
4X Nickel alloys
5X Titanium
6X Zirconium
7X Hard Facing Overlay

Note:- X represents any number 0 to 9

Reference: iiwindia literature and ASME Section IX

Keep reading, happy welding

Thank you,

KP Bhatt