Resiliently Seated Valves
Systems Engineering Division (CG-ENG-3)
Each Code of Federal Regulation (CFR) cited below is updated annually in a free searchable database available from the Government Publishing Office.
A resiliently seated valve (RSV) is a valve in which the closure of the line is accomplished by resilient nonmetallic material instead of a metal to metal seat. These valves are categorized and accepted by the U.S. Coast Guard based on intended service as per 46 CFR 56.20-15.
Positive Shutoff Valves:
Required Locations. Piping subject to internal head pressure from a tank containing oil must be fitted with positive shutoff valves located at the tank in accordance with 46 CFR 56.50-60(d). Otherwise positive shutoff valves may be used in any location in lieu of a required Category A or Category B valve.
Standard Test Procedure: For Positive Shutoff Valves, the standard test procedure requires:
- Removal of all resilient seating material;
- Testing at full rated pressure;
- Closed valve must pass through the line:
- For Liquid: < NPS · 10 ml/hr, or < NPS · 0.34 oz/hr
For Gas: < NPS · 3 l/hr, or < NPS · 0.11 ft3/hr
-
- where NPS is the nominal pipe size, in inches; and
- Packing material must be fire resistant.
Category A Valves:
Required Locations. Except where positive shutoff valves are required, Category A valves are required in each of the following locations:
- Valves at vital piping system manifolds;
- Isolation valves in cross-connects between two piping systems, at least one of which is a vital system, where failure of the valve in a fire would prevent the vital system(s) from functioning as designed;
- Valves providing closure for any opening in the shell of the vessel.
Standard Test Procedure: For Category A valves, the standard test procedure requires:
- Removal of all resilient seating material;
- Testing at full rated pressure; and
- Closed valve must pass through the line:
- whichever is greater, where qmax is the fully open flow rate and NPS is the nominal pipe size.
Vital Systems:
The term vital system is used in several places in U.S. regulations and other documents, sometimes without formal definition. A system should be regarded as vital if it must start or continue working to protect the vessel, personnel, or the marine environment from serious harm. Such systems generally include, but are not limited to, the following:
- Propulsion and necessary auxiliaries;
- Ship's service and emergency electrical generation and necessary auxiliaries;
- Steering;
- Firefighting;
- Bilge pumping;
- Cargo containment systems.
The term vital has sometimes been used incorrectly to describe hazardous systems. A hazardous system may or may not be considered vital. For example, a high-pressure air system used only for tools and industrial machinery might contain a great deal of stored energy capable of injuring personnel or even damaging the ship if it failed violently. However, this is not a vital system because it could be taken out of service at any time, even during a casualty or in a maneuvering situation, with no risk to personnel, vessels, or the marine environment. Non-vital hazardous systems may still be subject to other regulations just not those specific to vital systems.
Valve Acceptance Procedures:
General Acceptance. Valves are not issued a Certificate of Approval by the U.S. Coast Guard. Instead, the Marine Safety Center (MSC) determines if a valve is suitable for the intended purpose during engineering plan review for each vessel/system.
Test Procedures. There are three different methods that may be used to obtain acceptance by the MSC during plan review, with the flow rate performance test being the preferred method. Manufacturers are responsible for forwarding the test results along with all related documentation to the MSC in Washington DC to demonstrate that the valve complies with 46 CFR 56.20-15. The following are the only acceptable test methods for valves:
- Flow rate performance test for valves using the standard test procedures in 46 CFR 56.20-15(b), as outlined above.
- Fire test for soft-seated quarter-turn valves using the procedures in American Petroleum Institute (API) standard 607, fourth edition.
- Control valve capacity test using the procedures in ANSI/ISA S75.02-1996 to determine the value for the valve flow coefficient Cv.
Category B Valves:
Valves that do not provide effective closure of the line, or that permit appreciable leakage from the valve when the resilient material is damaged or destroyed, are Category B valves. Category B valves are not required to be tested and may be used in any location except where Category A or a Positive Shutoff Valve are otherwise required. Category A valves that fail to meet the requirements for positive shutoff are considered Category B.
Contact the Systems Engineering Division (CG-ENG-3):
Commandant (CG-ENG-3)
U.S. Coast Guard
2703 Martin Luther King Jr. Ave. SE STOP 7509
Washington, D.C. 20593-7509
Tel: +1 (202) 372-1367