Pressure Testing, Inspection and Quality Control
What this domain tests
This domain covers hydrostatic and pneumatic testing, non-destructive examination, inspection hold points, and documentation. The exam tests whether you know what to test, when to test, and what makes a test invalid.
Core rules
- Hydrostatic test pressure is commonly 1.5 times design pressure, but must not exceed the lowest-rated component; confirm the project specification and class rule.
- Test water must be clean and compatible with the material; stainless systems need controlled chloride content and thorough drying.
- Use calibrated gauges with a range that gives a readable mid-scale indication; vent high points and fill completely.
- Do not test before supports, anchors, and temporary restraints are in place.
- NDE methods include visual, radiographic, ultrasonic, magnetic-particle, and dye-penetrant inspection; each detects different defects.
Worked example
A line has a design pressure of 10 bar. The specification requires a hydrostatic test at 1.5 times design, so the test pressure is 15 bar. Check that valves, flanges, and instruments are rated for at least 15 bar, fill with compatible water, vent all high points, and pressurize slowly. Hold for the specified time, inspect all joints, and record gauge readings. Reasoning: the test proves strength and tightness, but overpressurizing a lower-rated component turns a valid test into a failure.
Traps
- Testing before permanent supports are installed.
- Using a gauge that is off-scale or out of calibration.
- Trapping air and mistaking it for a pressure drop.
- Performing a pneumatic test where a hydrostatic test is required without approval.