This standard covers inspection, examination, supplementary examinations, and pressure test requirements for resilient-seated, nonmetallic-seated (e.g. ceramic), and metal-to-metal-seated valves of the gate, globe, plug, ball, check, and butterfly types. Resilient seats are considered to be:
a) soft seats, both solid and semi-solid grease type (e.g. lubricated plug);
b) combination soft and metal seats;
c) any other type valve designed to meet resilient seat leakage rates as specified in Table 6.
API 598 supplements the API standards that reference it, but it may also be applied to other types of valves by agreement between the purchaser and the valve manufacturer.
The inspection requirements pertain to examinations and testing by the valve manufacturer and any supplementary examinations that the purchaser may require at the valve manufacturer's plant. The test requirements cover both required and optional pressure tests at the valve manufacturer's plant, or at a facility mutually agreeable to both the manufacturer and purchaser.
The following tests and examinations are specified in this standard:
a) shell test,
b) backseat test,
c) low-pressure closure test,
d) high-pressure closure test,
e) double block and bleed high-pressure closure test,
f) visual examination of castings by the manufacturer,
g) high-pressure pneumatic shell test.