API 594 - Check Valves: Flanged, Lug, Wafer, and Butt-Welding

Explore this topic

API Std 594, Check Valves: Flanged, Lug, Wafer, and Butt-welding, is a standard developed and published by the American Petroleum Institute (API) that covers the design, materials, face-to-face dimensions, pressure-temperature ratings, and examination, inspection, and testing requirements for Type "A" and Type "B" check valves. This standard was originally published in 1997, with the most recent 8th Edition being published in July of 2017.

  1. Type "A" check valves are short face-to-face, and can be wafer, lug, or double- flanged; single-plate or dual-plate; or gray iron, ductile iron, steel, nickel alloy, or other alloy designed for installation between Classes 125 and 250 cast-iron flanges as specified in ASME B16.1, between Classes 150 and 300 ductile-iron flanges as specified in ASME B16.42, between Classes 150 and 2500 steel flanges as specified in ASME B16.5, and between Classes 150 and 600 steel pipeline flanges as specified in MSS SP-44, or steel flanges as specified in ASME B16.47.

  2. Type "B" bolted-cover swing check valves are long face-to-face, and can be flanged or butt-welding ends of steel, nickel alloy, or other alloy material. End flanges shall be as specified in ASME B16.5, or ends shall be butt-welding as specified in ASME B16.25.

Related Topics

Relevant Links

Topic Tools

Share this Topic

Contribute to Definition

We welcome updates to this Integripedia definition from the Inspectioneering community. Click the link below to submit any recommended changes for Inspectioneering's team of editors to review.

Contribute to Definition

Subscribe to Inspectioneering

Downloads & Resources related to API 594 - Check Valves: Flanged, Lug, Wafer, and Butt-Welding

    Inspectioneering Journal

    Explore over 20 years of articles written by our team of subject matter experts.

    Company Directory

    Find relevant products, services, and technologies.

    Talent Solutions

    Discover job opportunities that match your skillset.

    Case Studies

    Learn from the experience of others in the industry.


    Inspectioneering's index of mechanical integrity topics – built by you.

    Industry News

    Stay up-to-date with the latest inspection and asset integrity management news.


    Read short articles and insights authored by industry experts.

    Expert Interviews

    Inspectioneering's archive of interviews with industry subject matter experts.

    Event Calendar

    Find upcoming conferences, training sessions, online events, and more.


    Downloadable eBooks, Asset Intelligence Reports, checklists, white papers, and more.

    Videos & Webinars

    Watch educational and informative videos directly related to your profession.


    Commonly used asset integrity management and inspection acronyms.