UG-98, MAWP and Liquid Static Head Calculations

Most process vessels contain operating fluids which produce liquid static head that must be accounted for when determining the design pressure P.  Paragraph UG-98 of the ASME® Code also requires that static liquid head be deducted when determining a pressure vessel’s maximum allowable working pressure (MAWP).  As the pressure due to liquid static head varies based on each individual component’s elevation, complying with this seemingly simple requirement quickly becomes a time consuming task.  The COMPRESS Automatic Liquid Level feature saves time and reduces errors by eliminating the need to manually calculate the location specific static head for every nozzle, flange, shell course and head situated below the normal operating liquid level (NLL).  Similarly, COMPRESS automatically deducts the correct local static head from each component’s UG-98 MAWP when determining the overall vessel’s rated MAWP.  This powerful feature has the added benefit of supporting multiple pressure chamber designs.  In this case, a separate liquid level and specific gravity may be specified for each vessel chamber.

Changes made to a liquid level in COMPRESS automatically flow through all affected aspects of the pressure vessel’s design and UG-98 rating.  In addition to re-calculating component static liquid heads, moving the liquid level or changing the specific gravity causes COMPRESS to update overhead weights, foundation loads and the period of vibration calculation.