Wall thickness, minimum allowable

Austenitic or duplex stainless steel pressure casing components may be hydrostatically tested with an additional amount of material on areas where machining to critical dimensions and tolerances is required. The additional amount of material shall not exceed 1 mm (0.040 in.) material stock or 5 percent of minimum allowable wall thickness, whichever is less. 

Minimum Allowable Wall Thickness—The minimum wall thickness required by DOT cylinder specification. 

Table 10-1. Original Minimum Allowable Wall Thickness for Certain Common Sizes of Low Pressure Cylinders.

A cylinder must be condemned when the remaining wall thickness in an area having isolated pitting is less than one-third of the original minimum allowable wall thickness. 

When the original wall thickness at manufacture is unknown and the actual wall thickness cannot be measured, a cylinder must be condemned if the cut, gouge, or dig exceeds one-half the minimum allowable wall thickness at manufacture (taken from Table 10-1). 

High pressure steel cylinders. Limits for cuts, gouges, or digs for high pressure steel cylinders are established by stress considerations. That is, a cylinder must be rejected when the remaining wall thickness is less than the minimum allowable wall thickness at manufacture, obtained using the maximum wall stress limitation de-... 

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. 

Minimum Allowable Wall Thickness— Minimum allowable wall thickness is the minimum wall thickness required by the specification under which the cylinder was manufactured. 

A cylinder must be condemned when line or crevice corrosion on the cylinder is 3 inches (7.6 cm) in length or over and the remaining wall is less than three-fourths of the original minimum allowable wall thickness, or when the line or crevice corrosion is less than 3 inches (7.6 cm) in length and the remaining wall thickness is less than one-half... 

Representative Cylinder Wall Thickness, To use the above criteria, it is necessary to know the minimum allowable wall thickness at manufacture. Table 9-1 provides the minimum allowable wall thickness for a number of common size low pressure steel cylinders. 

Original Minimum Allowable Wall Thickness ( ) inches (mm)... 

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