The Core Standards for Swing Check Valves
A swing check valve for oil, gas and general plant service is governed by a small family of API and ASME standards. API 6D, Specification for Pipeline and Piping Valves, covers the design, materials and testing of check valves for pipeline service. ASME B16.34 defines the pressure-temperature ratings and the general design rules for flanged and butt-welding end steel valves, including check valves. API 594 covers wafer, lug and flanged check valves, and API 598 defines the inspection and testing requirements that apply to all of them.
Design and Construction Requirements
Per API 6D, a swing check valve consists of a body, a hinged disc, a hinge pin, a seat and a cover or access opening. The disc swings away from the seat as forward flow develops and falls back onto the seat when flow reverses. Common body materials are ASTM A216 WCB carbon steel, A217 WC6 and WC9 chrome-moly steel for elevated temperature, A351 CF8 and CF8M stainless steel for corrosive service, and A352 LCB or LCC low-temperature steel. Trim materials such as 13 percent chromium steel, 316 stainless steel or stellite-faced seats are selected to match the media and the required seat hardness.
Ratings, Sizes and End Connections
Pressure ratings follow the ASME B16.34 class system from Class 150 up to Class 2500, and the maximum allowable working pressure at the design temperature is read directly from the material rating tables. End connections are flanged to ASME B16.5 up to 24 inches and ASME B16.47 above that, or butt-welding ends for fully welded pipelines, while wafer and lug bodies per API 594 fit between flanges. Face-to-face dimensions for flanged swing check valves follow ASME B16.10 so that valves from different suppliers can be interchanged in an existing pipe run.
Testing and Inspection per API 598
API 598 requires every check valve to pass a shell hydrostatic test at 1.5 times the rated pressure to prove body integrity, followed by a seat test with water or air at the pressure defined for the valve class. The test duration depends on the nominal valve size. Valves destined for critical service can additionally be supplied with radiography, ultrasonic or magnetic particle examination of castings and welds, and with material certificates traceable to the heat of the body casting. These tests are the final confirmation that the valve meets its rated pressure and leakage class before shipment.
Frequently Asked Questions
Q: Which API standard covers swing check valve design?
A: API 6D covers the design of check valves for pipeline service, while ASME B16.34 provides the pressure-temperature ratings and general design rules.
Q: What does API 594 cover?
A: API 594 covers wafer, lug and flanged check valves, including their dimensions, materials and testing requirements.
Q: Which testing standard applies to swing check valves?
A: API 598 defines the shell and seat pressure tests, test pressures and test durations for steel valves including swing check valves.
Q: What materials are typical for low-temperature swing check valves?
A: Low-temperature service uses A352 LCB or LCC castings with impact-tested materials rated for cold service conditions.
Q: How do I confirm the face-to-face dimension of a flanged check valve?
A: Flanged check valve face-to-face dimensions are given in ASME B16.10, which standardizes end-to-end lengths for interchangeability.
Q: Can a swing check valve be used for vertical flow?
A: Swing check valves are normally installed horizontally or in vertical upward flow so the disc opens freely, and vertical downward flow should be avoided.