Select at least six sample pipes of the kind you plan to use for natural gas, to use for materials testing.
Place one of the pipes within the clamps of a materials testing machine equipped to carry out tensile strength tests.The first clamp should go around the top of the round surface of the pipe and the second clamp should go around the bottom of the pipe.
Use the tensile stress testing option to instruct the machine to pull the two ends of the pipe apart at the weld. The machine will record the points at which the metal bonds of the weld start to break apart and at which the actual weld breaks. You must ensure that the load caused by the natural gas is less than either of these loads.
Clamp your pipe to a machine equipped to carry out bend testing. You must clamp sections of your pipe that are left and right of the weld to each of the clamps of your machine and instruct the machine to bend the pipe at the surface of the weld.
Determine whether or not the pipe breaks. Ideally, the weld is strong enough that the pipe does not break. However, if the pipe does break, record the breakage point. Again, make sure that the stress required to reach that point is less than the stress exerted by the natural gas that will be passing through your pipes.
Repeat the tensile stress test and the bend test, respectively, with two other pipes, to ensure the accuracy of your measurements.