Steel cylinders external visual inspection

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. 

Requirements concerning the external and internal inspection of low pressure and high pressure cylinders are discussed in the following sections. This material summarizes the inspection procedures provided in CGA C-6, Standard for Visual Inspection of Steel Compressed Gas Cylinders. [13] Except where noted, the focus of this presentation therefore pertains to low pressure and high pressure steel cylinders. While many of the same considerations are also pertinent to the inspection of aluminum cylinders and other types of cylinders made of materials other than steel, the respective CGA technical publications should be consulted for specific procedures and defect limitations concerning such cylinders. See CGA C-6.1, C-6.2, and C-6.3. [14], [15], and [16] Likewise, those concerned with the inspection of steel cylinders should refer to the most current edition of CGA C-6. [13]... 

Interior corrosion is best evaluated by a hydrostatic test combined with careful visual inspection. Thickness-measuring and flaw detection devices of the ultrasonic type may be used to evaluate specific conditions. Basic corrosion limits for both low and high pressure steel cylinders were discussed under the External Inspection section of this chapter. 

---