From Ludwig's Applied Process Design for Chemical and Petrochemical Plants, Volume 1, Fourth Edition

9.3 MATERIALS OF CONSTRUCTION

SAFETY AND RELIEF VALVES: PRESSURE-VACUUM-RELIEF VALUES

For most process applications, the materials of construction can be accommodated to fit both the corrosive-erosive and mechanical strength requirements. Manufacturers have established standard materials, which will fit a large percentage of the applications, and often only a few parts need to be changed to adapt the valve to a corrosive service. Typical standard parts are (see Figures 9-3a, 9-3b, and 9-4) as follows:

Option 1 (typical only)

Body

carbon steel, SA 216, gr.WCB

Nozzle

316 stainless steel

Disk/Seat

stainless steel

BlowDown

Ring 300 Ser. stainless steel

Stem or Spindle

stainless steel

Spring

C.S.rust proof or high temp.alloy, rust proof

Bonnet

SA-216, gr.WCB carbon steel

Bellows

316L stainless steel

Option 2 (typical only)

Body

316 stainless steel

Nozzle

17-4 stainless steel or 316 stainless steel

Disk/Seat

Teflon, Kel-F, Vespel or Buna-N

BlowDown Ring

316 stainless steel

Stem or Spindle

17-4 stainless steel or 316 SS

Spring

316 stainless steel

Bonnet

316 stainless steel

Bellows

For pressure and temperature ratings, the manufacturers' catalogs must be consulted. In high pressure and/or temperature, the materials are adjusted to the service.

For chemical service the necessary parts are available in 3.5% nickel steel; Monel; Hastelloy C; Stainless Type 316, 304, and so on.; plastic-coated bellows; nickel; silver; nickel-plated springs; and other workable materials.

The designer must examine the specific valve selected for a service and evaluate the materials of construction in contact with the process as well as in contact with...

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