IIAR 6 Appendix B Pressure Vessels Checklist | Part 5

Part 5: This is a continuation of our blog series explaining how to perform an IIAR 6 Appendix B inspection of an ammonia pressure vessel.


Items B and C on Page 2 of the checklist ask if the vessel is suitable for ammonia and operating within limits. The inspector must verify that the vessel is ASME-stamped and not constructed of materials, such as copper, that would degrade if exposed to ammonia. The two primary operating limits of concern are pressure and liquid level. The pressure should be at least 10% lower than the relief valve set pressure. The liquid level must have adequate vapor space to accommodate liquid expansion if the vessel experiences an unexpected heat load. As a good practice, RETA Book 1 recommends limiting the liquid level to no more than 80%. This leaves 20% of the vessel volume as room for expansion. The 80%/20% rule is based on the actual expansion change seen in anhydrous ammonia liquid that is stored at -65ºF and allowed to warm up to 125ºF.


The previous blogs in this series are available in the following links. You can watch our free video of how to perform an IIAR 6 Appendix B Pressure Vessel inspection here.

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