Non-Destructive Examination and Pressure Testing
Methods and acceptance
Non-destructive examination is performed to ASME Section V for method requirements and accepted to the construction code: Section VIII Div. 1 UW-51 and UW-52 for radiography, UW-53 for ultrasonics, Appendix 6 and 8 for magnetic particle and penetrant; ASME B31.3 Chapter VI for piping; API 598 for valves. Know each method's purpose. Radiography and ultrasonic testing find internal or volumetric flaws; magnetic particle finds surface and near-surface flaws in ferromagnetic material; penetrant finds surface-breaking flaws in any material; visual examination is the primary and most-used method. Personnel must be qualified under a recognized scheme, such as ASNT SNT-TC-1A or CP-189, with current records available.
Timing
The classic trap is sequence. Final NDE normally follows post-weld heat treatment and any major repair. Some specifications require magnetic particle or penetrant examination after the hydrotest to catch test-induced cracking. Radiographs must show adequate density, identification, and the required IQI. Spot radiography versus full radiography changes joint efficiency under UW-11 and UW-12; never accept a spot-shot report where the design assumed full radiography.
Pressure testing
Hydrostatic testing under UG-99 uses 1.3 x MAWP x (S at test temperature / S at design temperature), with the metal temperature at least 30 degrees F above the minimum design metal temperature and controls on test-water chlorides. Pneumatic testing is 1.1 x and stores far more energy, so exclusion zones and procedure review are essential.
Worked example
MAWP 300 psi at 650 degrees F; S at 650 degrees F is 18.8 ksi, S at test temperature is 20.0 ksi. Test pressure = 1.3 x 300 x (20.0 / 18.8) = 415 psi. An answer of 390 psi forgot the stress ratio.
Rule of thumb
Read the code paragraph before every test; hold time, gauge calibration, and temperature limits are requirements, not shop preferences.