What are Weld Test Coupons?

The pictures shown below are of weld test coupons which were recently used to test a welder’s skills. These pieces of metal called “coupons” have had straps cut out for destructive testing and then reattached to the coupon after they were tested.  For the weld procedure that those coupons were used for, there was a series of inspection criteria that must be met before the welder becomes qualified on that procedure.

 

First, the welder completes the root pass and it must be visually inspected (VT) and approved by the welding inspector before being allowed to proceed.  When the coupon is welded out, and a final visual acceptance of the weld is done, the weld is ready for either non-destructive testing (NDT) or destructive testing (DT) depending on the type of weld.  In this case, the 36” butt weld coupons required both NDT and DT.
For the NDT, the entire coupon was x-rayed (RT).  After passing the RT criteria, the coupon moved on to destructive testing.  For DT on these coupons, there was a total of 12 straps cut out and prepped for testing.  Eight straps were used for nick break tests, two straps for root bend tests, and two straps for face bend tests.
The nick tests are performed to expose internal imperfections such as slag inclusions, lack of fusion, incomplete penetration, porosity, etc. in the weld.  To do this, a notch or nick is intentionally made by a cutting the strap on the weld face to help it fracture in the center line of the weld.  The strap is then mechanically bent to fracture it and the cross section is visually examined for any imperfections.
The root and face bends are done in a similar fashion, but used to test the ductility of the weld with the base material.  One set of straps is bent with the face of the weld to the outside, and the other set is bent with the root of the weld to the outside.  The idea here is that the weld metal and base material should plastically deform together, and not fracture or fail.  After being mechanically bent, if the straps do not fail, they are visually examined for any imperfections as well.
After successfully completing all these requirements, the welder is determined to be qualified for the procedure being tested.

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