Aluminum cylinders, inspection

The aluminum cylinder was made of 6161 aluminum alloy in 1989. It was taken out of service after 5 yr because it failed a safety test due to high moisture content (>200 ppm). An optical probe inspection (with mirror and a light source) revealed internal corrosion. Figure 7.6 is a photo of the aluminum cylinder before it was opened. 

The following sections summarize the inspection procedures provided in CGA C-6, Standards for Visual Inspection of Steel Compressed Gas Cylinders [10]. Except where noted, the focus pertains to low pressure and high pressure steel cylinders. While many of the same considerations apply to the inspection of aluminum cylinders and 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, andC-6.3 [11, 12, 13]. 

As previously stated, considerations for visual inspection of steel cylinders are also applicable to aluminum cylinders. However, some differences exist with acceptance criteria. For example, aluminum cylinders must be condemned when impairment to the surface (corrosion or mechanical defect) exceeds a depth so that the remaining wall is less than three-fourths of the minimum allowable wall thickness required by the specification under which the cylinder was manufactured. 

CGA C-6.1 and CGA C-6.3 provide details on the requirements for inspection of aluminum cylinders. Other publications such as CGA C-6.2 provide similar information for cylinders made of composite materials [11, 13, 12]. 

C-6.3 Guidelines for Visual Inspection and Re-qualification of Low Pressure Aluminum Compressed Gas Cylinders. Provides data and details as a guide for the periodic inspection of aluminum cylinders with a service pressure of 360 psi (2482 kPa) or less. Contains color photos of defects. Current edition cited in 49 CFR (9 pages). 

This discussion may not cover all conditions, sizes, types of defects, or methods of inspection. More complete and specific coverage of the subject is found in CGA C-6, Standards for Visual Inspection of Steel Compressed Gas Cylinders, and 49 CFR 173.34 and 173.301 [10, 1]. For cylinders made from materials other than steel, see CGA C-6.1, Standards for Visual Inspection of High Pressure Aluminum Compressed Gas Cylinders , CGA C-6.2, Guidelines for Visual Inspection and Requalification of Fiber Reinforced High Pressure Cylinders , CGA C-6.3, Guidelines for Visual Inspection and Requalification of Low Pressure Aluminum Compressed Gas Cylinders , CGA C-8, Standardfor Requalification of DOT-3HT, CTC-3H, and TC-3HTM Seamless Steel Cylinders , and CGA C-13, Guidelines for Periodic Visual Inspection and Requalification of Acetylene Cylinders [W, 12, 13, 14, 15]. 

CGA C-6.1, Standards for Visual Inspection of High Pressure Aluminum Compressed Gas Cylinders [11]... 

CGA C-6.3, Guidelines for Visual Inspection and Requalification of Low Pressure Aluminum Compressed Gas Cylinders, ed., Compressed Gas Association, Inc., 1725 Jefferson Davis Highway, Arlington, VA 22202. 

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]. ... 

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