Corrosion or pitting. Corrosion or pitting in cylinders involving the loss of wall thickness by corrosive media.

Note:

There are several kinds of pitting or corrosion to be considered.

Cuts, gouges, or digs (in cylinders). Deformations caused by contact with a sharp object in such a way as to cut into or upset the metal of the cylinder, decreasing the wall thickness at that point.

Dents (in cylinders). Deformations caused by the cylinder coming in contact with a blunt object in such a way that the thickness of metal is not materially impaired.

DOT. The U.S. Department of Transportation.

General corrosion. Corrosion which covers considerable surface areas of the cylinder.

Note:

It reduces the structural strength. It is often difficult to measure or estimate the depth of general corrosion because direct comparison with the original wall cannot always be made. General corrosion is often accompanied by pitting.

High- and low-pressure cylinders. Those cylinders with a marked service pressure of 900 p.s.i. or greater; low-pressure cylinders are those with a marked service pressure less than 900 p.s.i.

Isolated pitting. Isolated pits of small cross-section which do not effectively weaken the cylinder wall but are indicative of possible complete penetration and leakage.

Note:

Since the pitting is isolated the original wall is essentially intact.

Line corrosion. Pits which are not isolated but are connected or nearly connected to others in a narrow band or line.

Note:

This condition is more serious than isolated pitting. Line corrosion frequently occurs in the area of intersection of the footring and bottom of a cylinder. This is sometimes referred to as "crevice corrosion."

Minimum allowable wall thickness. The minimum wall thickness required by the specification under which the cylinder was manufactured.

PDFWAC 296-24-92001

Definitions.