Welding Variables procedure for SMAW

Welding Variables procedure for Shielded metal arc welding (SMAW)

Variables:-

Variable is a situation, number, or quantity that can vary or be varied. All the necessary parameters like joint, base metal, filler metal, preheat post-weld heat treatment, positions, electric characteristics, technique, etc.

There are three types of variables that are used in welding procedure specification (WPS).

1. Essential variables.

2. Non-essential variables.

3. Supplementary variables.

1. Essential variables:-

Essential variables are those variables in which make changes considered to affect the mechanical properties of the weld metal, So any changes shall be required

Each and every welding process have a different essential variable, a change from one welding process to another welding process is essential and required to

Contents which are mentioned in WPS -

Note:- Every welding process has the same content, but variables are different.

1.1 Joint.

1.2 Base metal.

1.3 Filler metal.

1.4 Positions.

1.5 Preheat.

1.6 PWHT (Post weld heat treatment).

1.7 Electrical characteristics/ Gas.

1.8 Technique. 

Here a take an example of essential variables for Shielded metal arc welding (SMAW), when it will be changed then need the requalification of WPS.

1.1 Joints:-

(a) There are no essential variables in the joint.

1.2 Base metal:-

(b) Change in thickness qualified.

(c) t pass > 13 mm.

(d) Change in P number qualified.

1.3 Filler metal:-

(c) Change in the deposited weld metal.

1.4 Positions:-

(a) There are no essential variables in Positions.

1.5 Preheat:-

(a) Decrease > 55 degree centigrade

1.6 PWHT (Post weld heat treatment):-

(a) Change in post-heat weld treatment (PWHT).

(b) Thickness limit.

1.7 Electrical characteristics:-

(a) There are no essential variables in electrical characteristics.

1.8 Technique:-

(a) Use of the thermal process.

2. Non Essential variables:-

Non Essential variables are those variables in which make changes considered to not affect the mechanical properties of the weld metal, So any changes shall not require requalification of the welding procedure.

Each and every welding process have a different non-essential variable, a change from one welding process to another welding process is in non-essential variables not required to requalification.

Here a take an example of non-essential variables for shielded metal arc welding (SMAW).

Note:- All the content which is mention in the Welding procedure specification (WPS) for shielded metal arc welding (SMAW), the same for all three variables. So.

2.1 Joints:-

(a) Change in groove design.

(b) deletion of backing in single welded groove weld. Double welded are consider welded with backing.

(c) Change in root spacing.

(d) Addition or deletion of retainers.

2.2 Base metal:-

(a) There is no non-essential variable in the base metal.

2.3 Filler metal:-

(a) Change in diameter. 

(b) Change in classification.

2.4 Positions:-

(a) Change in positions uphill and downhill vertical welding.

2.5 Preheat:-

(a) Extra add in positions.

(b) Change in preheat maint.

2.6 PWHT (Post weld heat treatment):-

(a) There is no non-essential variable in PWHT.

2.7 Electrical characteristics:-

(a) Change in intensity of current (I) and voltage (E).

(b) Change in current and polarity.

2.8 Technique:-

(a) Change in strive or wave.

(b) Change in Method of cleaning.

(c) Change in method of back gauge.

(d) Change in manual or automatic.

(e) Addition or deletion of peening.

(f) Change in multiple to single pas/side.

3. Supplementary variables:-

The supplementary essential variable becomes an additional essential variable in conditions, where procedure qualifications require notch-toughness testing for each and every welding process. in which a change will affect the toughness properties of the joint, heat affected zone, and base material, etc.

3.1 Joints:-

(a) There are no supplementary variables in the joint.

3.2 Base metal:-

(b) Thickness limit impact.

3.3 Filler metal:-

(b) Change in classification.

3.4 Positions:-

(a) Change in positions.

3.5 Preheat:-

(a) Increase >55 degree centigrade (IP).

3.6 PWHT (Post weld heat treatment):-

(a) Change in post-heat weld treatment (PWHT) (weld coupon thickness & thickness range).

3.7 Electrical characteristics:-

(a) Increasing heat input.

(b) Change in current and polarity.

3.8 Technique:-

(a) Change in multiple to single pass or slide.

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