Pipes are subjected to extreme loads in the pipelines linking production regions with Europe. Tests on pipes and pipe material are precisely defined in accordance with the requirements of API5L; while these include flexure tests, impact and drop-weight tests and hardness tests, the tensile test is the essential component of quality control.
Options for testing tensile specimens consisting of or taken from pipes vary according to the shape of the product. Small, thin pipes are flattened at each end for a sufficient length and then pulled, while cores are used for larger diameters to avoid pre-damage due to crushing. With large pipes, material is removed from the pipe wall and standard specimens produced from it. Curvature to the pipe radius may be present in specimens extracted longitudinally; to achieve reliable testing, with no pre-damage, this curvature must where necessary be compensated for with suitable shims. Global Pipe manufactures pipes up to 130 mm wall thickness, so the company has opted for a Zwick Z 1600E testing machine, maximum force 1600 kN.
The Z 1600E’s large measurement range allows small test forces to be determined accurately without re-equipping the materials testing machine. Large travel combined with relatively low overall height ensures trouble-free specimen clamping and convenient testing of a wide range of specimen lengths. Low-maintenance ball screws, pre-loaded for elimination of backlash, ensure precision long-term operation in the tensile and compression directions, while the extremely robust load frame offers a high degree of stiffness.