A Smarter Approach to Pump Casing Pressure Testing
Hydrostatic testing is the final quality verification before a pump casing leaves the factory—the proof that the pressure-containing structure can withstand the maximum allowable working pressure (MAWP) with an appropriate safety factor. But how the test is conducted matters. A detailed review of ASME and API pressure-testing requirements reveals that the treatment of auxiliary components—specifically, casing priming valves—can create unnecessary costs without improving test quality.
The Problem
Traditional practice at many pump manufacturers is to remove casing priming valves before hydrostatic testing, test the casing with the priming connection plugged, then reinstall the valves after the test. This practice wastes the valves (which must often be scrapped after removal), adds labor cost, and—most importantly—means the casing is tested in a configuration that does not match the as-built assembly. The test verifies the casing with a plug; the pump operates with a valve.
The Optimized Procedure
The engineering assessment evaluated an alternative procedure: leave the casing priming valve installed and fully open during the hydrostatic test, with a pressure-rated plug installed at the valve outlet. This approach:
- Eliminates valve removal and reinstallation labor—saving 1-2 hours per casing tested
- Preserves the valve for service—no unnecessary scrapping of functional components
- Tests the threaded or flanged connection between the valve and the casing—the as-built configuration—which the traditional method does not verify
- Maintains full test integrity—the pressure-rated plug at the valve outlet contains the test pressure, and the valve internals see the same pressure on both sides (no net force to damage the valve)
ASME and API Compliance
Both ASME B16.34 (Valves—Flanged, Threaded, and Welding End) and API 598 (Valve Inspection and Testing) provide requirements for pressure testing of valves. The key question: does the hydrostatic test pressure applied through an open valve exceed the valve’s rated shell test pressure? For most ANSI pump casings with a hydrostatic test pressure of 1.5× MAWP (typically 275-375 psi for standard ANSI B73.1 casings), the test pressure is well within the shell test rating of a Class 150 or Class 300 valve, which is tested at 1.5× the cold working pressure rating (typically 300-750+ psi).
Implementation and Results
The optimized procedure has been successfully implemented across manufacturing applications involving water and seawater pump casings. The benefits include:
- Reduced valve procurement cost (valves are not scrapped after testing)
- Reduced labor cost (no valve removal/reinstallation)
- Improved test validity (casing tested in as-built configuration)
- No increase in test failure rate or in-service leakage at priming valve connections
Key Takeaways
- Removing casing priming valves before hydrostatic testing is an unnecessary practice that wastes components and labor.
- Leaving the valve installed and open, with a pressure-rated plug at the outlet, tests the as-built assembly while protecting the valve internals.
- For standard ANSI pump casing test pressures (1.5× MAWP, typically 275-375 psi), the test pressure is well within the shell test rating of standard Class 150/300 valves.
- The optimized procedure has been validated in production and provides a model for re-evaluating other traditional manufacturing practices that may no longer be justified.