Physics Division

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Introduction

Reference Material

Policy and Requirements

Methods of Compliance

Operational Requirements

Appendices

1.

Properties of Liquids

2.

Relief Valve Sizing

2a.

Convective Heat Transfer

2b.

Relief Vent Pressure Drops

3.

Oxygen Deficiency Hazards

4.      METHODS OF COMPLIANCE

 4.1    Vendor-Supplied System and Equipment

 In the case of vendor-supplied systems and equipment, vendors shall provide documentation needed: 

  1. To demonstrate compliance with the safety criteria.
  2. To provide information required to complete a safety analysis of the system or component in final, installed configuration, and to estimate interaction with any connected systems.

4.2    Relief Valve Sizing

 Pressure relief valves must be installed on all vessels and piping which contain cryogenic fluids or might under some failure conditions contain cryogenic fluids (e.g. cryostat vacuum vessels).  Note that current standards require pressure relief devices to be ASME code-certified.

Several steps are involved in determining flow requirements for relief valves:

  1. Establish the maximum safe working pressure (MSWP) for all piping and vessels that may contain cryogenic fluids.  Note that current standards require that any cryogenic storage vessel be designed by the rules of Section VIII of the ASME Pressure Vessel Code
  2. Determine the maximum rate of efflux of the contained cryogenic fluid required to maintain pressure below the MSWP in a worst-case failure scenario.  Failure scenarios might include:
    • Failure of a cryostat insulating vacuum to atmosphere.
    • Failure of a cryostat insulating vacuum to the contained cryogen.
    • Flow of cryogen from a connected system due to a valve failure or operator error.
    • Trapping of cryogenic fluid due to valve failure or operator error.
  3. Show that the relief valves, as actually installed, provide sufficient relief capacity.  For high flow rates, the pressure drop in any plumbing leading to the relief valves may need to be considered.  Flow capacity should be estimated for the particular gas involved, at the appropriate temperature and pressure