Figure 9-63 shows gasket material used for fixed joints. At one time, fixed joints could be satisfactorily sealed with gaskets of compressed asbestos sheet packing (view A fig 9-63)

Today the 15 percent rubber content of the packing makes it unsatisfactory for modern, hightemperature, high-pressure equipment. Two types of gaskets (metallic or semimetallic) are in use in present day high-temperature and high-pressure installations. Gaskets of corrugated copper or of asbestos and copper are sometimes used on lowand medium-pressure lines.

Serrated-face metal gaskets (view B of fig 9-63) made of steel, Monel, or soft iron have raised serrations to make a better seal at the piping flange joints. These gaskets have resiliency. Line pressure forces the serrated faces tighter against the adjoining flange. The gaskets shown are of two variations.

Spiral-wound, metallic-asbestos gaskets (view C of fig 9-63) are made of interlocked strands of preformed corrugated metal and asbestos strips, spirally wound together (normally called the FILLER), and a solid metal outer or centering

Figure 9-63.-Fixed-joint gaskets. A. Sheet asbestos gaskets. B. Serrated-face metal gaskets. C. Spiral-wound, metallic-asbestos gaskets.

ring (normally called the RETAINING RING). The centering ring is used as a reinforcement to prevent blowouts. The filler piece is replaceable. When renewing a gasket, you should remove this piece from the retaining metal ring and replace it with a new filler. Do not discard the solid metal retaining outer or centering ring unless it is damaged. You can compress the gaskets to the thickness of the outer or centering ring.

When renewing a gasket in a flange joint, you must exercise special precautions when breaking the joint, particularly in steam and hot water lines, or in saltwater lines that have a possibility of direct connection with the sea. Be sure to observe the following precautions:

1. No pressure is on the line.

2. The line pressure valves, including the bypass valves, are firmly secured, wired closed, and tagged.

3. The line is completely drained.

4. At least two flange-securing bolts and nuts diametrically opposite remain in place until the others are removed, then slackened to allow breaking of the joint, and removed after the line is clear.

5. Precautions are taken to prevent explosions or fire when breaking joints of flammable liquid lines.

6. Proper ventilation is ensured before joints are broken in closed compartments.

These precautions may prevent serious explosions, severe scalding of personnel, or flooding of compartments. You should thoroughly clean all sealing and bearing surfaces for the gasket replacement. Check the gasket seats with a surface plate, and scrape as necessary. This affords uniform contact. Replace all damaged bolt studs and nuts. In flange joints with raised faces, the edges of gaskets may extend beyond the edge of the raised face.