A welding procedure specification (WPS) is a document that provides parameters for welding, including joints, metals, positions, and variables. There are three types of variables: essential, non-essential, and supplementary essential. Essential variables require requalification if changed, while non-essential variables can be changed without requalification. WPS and procedure qualification records (PQR) are qualified according to material groups designated by P-numbers, with PQR tests needed to support welding between specific P-number combinations. Qualification with a given P-number tests qualifies welding within certain P-number ranges depending on materials and filler metals used.

2. What is a WPS
A WPS is a written qualified welding procedure prepared to provide direction for making production welds to Code
requirements
A welding procedure specification is a written document providing direction to the welder (or welding operator). It
contains all the necessary parameters viz. joints, base metals, filler metals, positions, preheat, PWHT, gas etc.
(including ranges, if any) under which the welding process must be performed. These parameters are known as
variables (as per ASME Section IX). Three types of variables are mentioned in the code, these are;
1. Essential Variable
2. Non essential Variable
3. Supplementary Essential variable

3. Essential Variables
A change in essential variable is considered to affect the mechanical properties of the weldment and shall require
requalification of the WPS. Hence, the WPS must be required qualification, if any the essential variable is changed.
Supplementary Essential Variables
A change in the supplementary essential variable will affect the toughness properties of the joint, heat-affected zone,
or base material. Hence supplementary essential variables become additional essential variables in situations where
procedure qualification requires toughness testing. When procedure qualification does not require the addition of
toughness testing, supplementary essential variables are not applicable.
Nonessential Variables
Nonessential variables are those in which a change can be made without requalification of the existing WPS, since it is
not considered to affect the mechanical properties of the joint. Though a change in the nonessential variable doesn’t
require requalification of the WPS but still it should be properly addressed in the welding procedure specification
(WPS).

4. Important Tips Regarding to WPS & WPQ.
• While welding ASTM A 105 flange to ASME SA 516 base metal
Both these materials have P number 1.So our WPS may specify Base metal of P number 1 to P number 1.To
support this WPS,PQR test coupon welded using any of P number 1 base metal to any of P number 1 base metal. For
example we can choose ASME SA36 plates as our PQR test coupon since its P number is 1.If this PQR has Qualified,
then this WPS can be used for any metal assigned to P number 1,Welded to itself or any other P number 1 material.
For a welder, If he Weld a Test Coupon of material P - No. 1 through P - No. 15F, P - No. 34, or P - No. 41 through P -
No. 49, He will qualify for Welding any material P - No. 1 through P - No. 15F,P - No. 34, and P - No. 41 through P -
No. 49.
• While welding ASTM A 105 Forging to ASME SA 240 type 304 shell
ASTM A 105 has P number 1 and SA 240 TP 304 has P number 8. So our WPS may specify Base metal of P
number 1 to P number 8. To support this WPS,PQR test coupon welded using any of P number 1 base metal to P
number 8 base metal. For example we can choose our PQR test coupon as ASME SA36 plates to SA 240 TP 304 plate.
But it does not qualify either P number 1 to P number nor P number 8 to P number 8.

5. • While welding ASME A 106 pipe welded to ASME SA 335 P11 pipe
ASTM A 105 has P number 1 and ASME SA 335 P11 has P number 4. So our WPS may specify Base metal of
P number 1 to P number 4. a P number 4 PQR Test Coupon(ASME SA 335 GR.11 plate) will qualify the WPS for P
number 4 to P number 4 ,and P number 4 to P number 3 and P number 4 to P number 1.
P number Test Coupon will not, however, qualify the P number 3 to P number 3 nor P number 1 to P number 1,nor P
number 3 to P number 1
• While welding AISI 1018 plate material, an Unassigned metal, to welded to ASME A 106 pipe
Since ASME A 106 has P number 1,a P number 1 to AISI 1018 PQR test coupon will qualify the WPS to weld
AISI 1018 materials to weld with any P number 1 base metals.
• The welding application in Figure 10.1 is a P-Number 4 base metal.
The Welder may use a P-Number 1 base metal as the WPQ test coupon, which will qualify the welder for all
P-Number 1 through P-Number 11, P-Number 34 and P-Number 41 through 47 metals.
Although this is the full range allowed by the Code, it is not practical to expect a single qualification to cover
all of these applications. For example, a Code user would not prepare a WPS, to weld using an F-Number 3 filler metal
to weld on P-Number 8 base metals (austenitic stainless steels). Some of the ENiCrFe-XX series of filler metals may be

6. able to cover the full range of base metals. But they were not intended to allow an E6010, F-Number 3 filler metal to
weld on that full range of base metals.
• The welding application is a P-Number 1 to a P-Number 3 base metal. The Code user
Chose an ASME SA-106 Gr. B (P-Number 1) carbon steel pipe as the test coupon. The welder used an AWS
A5.1 E6010 electrode an F-Number 3 filler metal. The Code user specified the welder’s base metal qualification range
with the F- Number 3 filler metal to cover P-Number 1 and P-Number 3 base metals only. The Code user does not
expect to develop a WPS using a F-Number 3 filler metal to weld metals from any other P-Number groups of base
metals. This is how a Code user may sensibly limit the WPQ.
• The welding application is a P-Number 5A base metal welded with a F-Number 4 filler metal.
The Code user selected the ASME SA-106 Gr. B pipe again, but with an AWS A5.1 E7018 (F-Number 4) filler
metal. The Code user specified on the WPQ that this welder was qualified for P-Number 1 through P-Number 5 base
metals.

7. • The welding application is a P-Number 8 base metal welded with a F-Number 5 filler metal.
The Code user used the ASME SA-106 Gr. B pipe again, but with an AWS A5.4 E308-16 (F-Number5) filler
metal. The Code user specified on the WPQ that this welder was qualified for P-Number 1 through P-Number 11 base
metals. The Code user may eventually have applications with this range of base metals, and some of the F-Number 5
filler metals are capable of welding this full range of base metals. The only filler metals normally used to weld the P-
Number 1 through P-Number 11, P-Number 34 and P-Number 41 through 47 are the F-Number 4X series nickel-base
filler metals. A welder qualified with a F-Number 4X filler metal could have the full range of base metals allowed by QW-
423 specified on the WPQ.