Steel cylinders hydrostatic testing

Metrication also affects the specified ratio for hydrostatic test pressure, but does not increase the maximum test pressure. While high pressure seamless steel cylinders marked to CTC specifications are still tested to 5/3 service pressure, such cylinders marked to metric standards are retested at 1.5 times service pressure because the marked metric service pressure is 10 percent higher. 

Interior corrosion is best evaluated by a hydrostatic test combined with careful visual inspection. Ultrasonic thickness-measuring and flaw-detection devices may be used to evaluate specific conditions. Corrosion limits for both low and high pressure steel cylinders were dis-... 

DOT and TC regulations require the hydrostatic testing of compressed gas cylinders by water jacket or other suitable methods that provide accurate data [1, 2]. The hydrostatic test determines the total expansion and permanent expansion under specified test pressure. These expansion readings determine wall thickness, average wall stress, and level of yield strength of the steel. DOT or TC must approve in writing the type and operation of the test apparatus. 

Specification 3A, 3AA, and 3B cylinders used in methylamine service must be requalified by hydrostatic retest every 5 years under present regulations. Specification 4B, 4BA, and 4BW must be hydrostatically tested after expiration of the first 12-year period and each 7 or 12 years thereafter depending on the initial hydrostatic test method. Cylinders in compliance with specifications 3A, 3AA, 3B, 4B, 4BA, or 4BW that are used specifically for monomethylamine, dimethylamine, and trimethylamine service and are free from corroding components may also be qualified by an external visual inspection as described in CGA C-6, Standards for Visual Inspection of Steel Compressed Gas Cylinders [10]. Periodic hydrostatic retest is not required for specification 3E cylinders. 

---