Hydrostatic testing is the most common procedure used to qualify newly manufactured cylinders, spheres and tubes used for the transportation of dangerous goods. Hydrostatic testing is also required periodically to re-qualify these pressure vessels for continued service. During a hydrostatic test, a pressure vessel is placed inside a closed system, usually a test jacket filled with water, and a specified internal water pressure is applied to the container inside this closed system. The applied internal pressure causes an expansion of the container being tested, and the total and permanent expansion that the container undergoes are measured. These volumetric expansion measurements, in conjunction with an internal and external visual inspection of the container, are used to determine if a pressure vessel is safe for continued use, or has suffered from a degradation in its structural integrity and must be condemned.