How to qualify Tack Welder?


What is Tack Weld?

Tack Weld are either a permanent weld or temporary weld, welded to hold the pieces of a weldment or component assembly in right alignment until the final welds are completed. When a tack weld is temporary, they are removed by grinding before making the actual welding. Permanent tack welds become the part of the weld as they are fused during the welding run. Such Tack welds those are incorporated in the weld need to be of the acceptable quality level as applicable for the actual weld. As stated in AWS D1.1, When RT is used, no tack welds shall be in test area of the WQT coupon.

Often tack welds are used in stainless steel welds joints to limit the shrinkage. Tack welds are also used to hold parts during welding to prevent weld cracking due to weld stresses. Tack welds incorporated into final welds shall be made with electrodes meeting the requirements of the final welds. These welds shall be cleaned prior to incorporation. Multipass tack welds shall have cascaded ends or be otherwise prepared for incorporation into the final weld.

Who is a Tack welder?

AWS D1.1 defines tack welder as:

‘fitter, or someone under the direction of a fitter, who tack welds parts of a weldment to hold them in
proper alignment until the final welds are made.”

Tack welder qualification is mandatory in fabrication to ensure the tack welder’s ability to produce sound tack welds. The WQT for tack weld qualification is not intended to be used as guides for welding or tack welding during actual fabrication. The actual tack welding on job shall be performed in conformance with a qualified WPS only.

Preheating for Tack Welds

Tack weld require same preheat as required for base metal. The rational is that tack weld also produce same heat input as induced by the full weld. Materials such as Cr-Mo, HSLA or high carbon steel for example, if not preheated before tack weld can result in the welding cracking in the tack welds. As well as they will produce very high hardness HAZ and weld metal.

Click here to know What shall be the minimum & maximum length of tack welds

Qualification of tack welder according to ASME Section IX

ASME Section IX does not call separate qualification for Tack Welder. As per ASME Section IX, clause QW-303.1 Groove Welds, welders who are qualified for groove welds are also qualified to make tack welds in groove and fillets within the range qualified. Similarly, welder who are qualified for Fillet weld are only qualified to make tack welds in fillet welt joints.

As per the ASME Section IX, table QW 461.9 welder who qualify groove weld on plate can weld tack welds in groove, fillet on plates and pipes.

Qualification of tack welder according to AWS D1.1

AWS D1.1 require separate qualification for tack welder and does not accept qualification based on groove weld or fillet weld qualified welder. As per the AWS D1.1, clause 6.16.1.2 Tack Welders, A tack welder shall be qualified by one test plate in each position in which the tack welding is to be performed.

As per AWS D1.1, clause 6.16.2.2, tack welder shall make a 1/4 in [6 mm] maximum size tack weld approximately 2 in [50 mm] long on the fillet-weld-break specimen.

tack welder who passes the fillet weld break test shall be qualified to tack weld all types of joints (except CJP groove welds, welded from one side without backing; e.g., butt joints and T-, Y-, and K-connections) for the process and in the position in which the tack welder is qualified. Tack welds in the foregoing exception shall be performed by welders fully qualified for the process and in the position in which the welding is to be done.

tack weld length

Range of Tack Welder Qualification as per AWS D1.1

A tack welder who clears the fillet weld break test shall be qualified to tack weld all types of joints (except CJP groove welds, welded from one side without backing; e.g., butt joints and T-, Y-, and K-connections) for the process and in the position in which the tack welder is qualified. Tack welds in the foregoing exception shall be performed by welders fully qualified for the process and in the position in which the welding is to be done.

The essential variables for tack welder qualification according to AWS D1.1 are given in Table 6.12 as shown in the below figure.

Click here for Acceptance of Tack Welder qualification

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