Weld Inspection

For the beginner or the pro, periodic weld inspection should be routine. But for the beginner, the best way to learn is to watch as their welds are put under pressure and deformed until the weak spot is found. This is known as destructive testing. In destructive testing, test “coupons” are made out of the same material that eventually be welded and then put through a guided bend test that uses a hydraulic or pneumatic device that has two rollers on either side of the ram portion of the cylinder that the plate rests upon. The weld is centered under the ram as it comes down. The rollers allow the plate to rotate downward bending the weld into a U shape, as it travels down . The beginner should evaluate the types of welds that he or she will be making, and determine a proper testing method for it. As we discussed, usually a hydraulic guided bend test is used to perform destructive testing on a weld. But it isn't always necessary to have expensive equipment to make a simple bend test because it may not be practical or available. A good vise and heavy 3-6 lb hammer is all that is needed. To test a weld, begin by grinding the surface and bottom of the weld smooth and flush with the top of the plate. Then, simply place a test coupon into the jaws of the vice to the bottom of the weld. Once it is fully bent, take the large hammer and begin pounding the top edge of the coupon. As the plate bends, watch for splits, cracks and tears along the weld seam. IF more than a total of 1/8” of flaw is found along a 6 inch plate, then the weld is no good. For extra measure, if possible, straighten out the plate after it is fully bent and bend it the other way. If it survives both directions of bend, then it is sound. As a note, when grinding, make sure that you don’t encounter any small specks of porosity as well, as these will cause breakage as well. On the surface, the weld may look perfect, but once the weld is ground flat, the porosity will usually show up. There are many ways to test a weld, that include highly scientific devices such as xrays and ultrasounds that examine welds, instead of destroy them. These methods are non destructive in nature and are usually reserved for highly critical welds such as in a pipe line or a nuclear reactor, that of course can’t be examined any other way. Also there are tensile strength tests and fatigue testing and a nick break testing