Cylinders external visual inspection

The first category covers cylinders exempted from hydrostatic retesting requirements of DOT and TC by virtue of their exclusive use in non-corrosive gas service. Since they are not subject to internal corrosion they do not require internal shell inspection, and, therefore, can be requali-fied by an external visual inspection. However, if internal corrosion is suspected, cylinders of this type should be internally inspected and hydrostatically tested. 

An external visual inspection must be performed to ensure the cylinder is free of arc bums, evidence of exposure to fire or excessive heat cuts digs gouges dents corrosion pit-... 

Cylinders made in compliance with TC/DOT specifications 4, 3A, 3AA, 3A480X, 4A, or 4AA480 used exclusively for ammonia of at least 99.95 percent purity may, in lieu of hydrostatic retest, be given a complete external visual inspection at the time such periodic retest becomes due. See 49 CFR 173.34 (e)(13), (e)(14) [9]. 

External visual inspection as described in CGA C-6, Standards for Visual Inspection of High Pressure Aluminum Compressed Gas Cylinders, is permitted in lieu of the periodic retest provided cylinders used exclusively for ammonia of 99.95% purity. Subsequent inspections are required at 5 year intervals [12]. ... 

External visual inspection may be used in lieu of hydrostatic retest for cylinders that are used exclusively for inhibited... 

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. 

External visual inspection may be used in lieu of hydrostatic retest for cylinders that are used exclusively for inhibited 1,3-buta-diene which is commercially free from corroding components and that are of the following types (including cylinders of these types with higher service pressure) DOT 3A, 3AA, 3A450X, 3B, 4B, 4BA, 4BW. Continued use of existing cylinders of the ICC-26-240 and 26-300 types is authorized, but no new construction is authorized. 

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. 

DOT and TC state that results of required periodic inspections of a cylinder must be recorded, and a copy kept by the owner or the owner s authorized agent either until the expiration of the retest period or until the cylinder is again reinspected or retested, whichever occurs first [1, 2]. Also, a cylinder that passes the re-qualification procedure must have the date permanently stamped on the cylinder in the prescribed manner. Note An E is to follow the date (month and year) when requalification by the visual external inspection method is allowed in lieu of hydrostatic retesting. 

As previously discussed, DOT and TC regulations both specify that the periodic retest must include an external and internal visual examination of the cylinder. It is recommended that these inspections be conducted prior to the hydrostatic retest. 

Regardless of the type of hydrostatic testing method used, DOT and TC regulations both specify that the periodic retest must include an external and internal visual examination of the cylinder. It is recommended that these inspections be conducted prior to the hydrostatic retest in accordance with the applicable Compressed Gas Association standards. See references [13] through [16] and [20]. External and internal inspection considerations were discussed more thoroughly in previous sections of this chapter. 

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