Inspection, Testing, and Commissioning
This domain tests pressure testing, tightness testing, purging, combustion commissioning, and the records that prove the system is ready.
Core rules
- Distinguish strength testing from tightness/leak testing. Strength tests verify mechanical integrity; tightness tests verify leak-tightness at a lower pressure.
- Use air, nitrogen, or an inert gas for pneumatic testing unless the code and procedure permit otherwise; never use fuel gas as a test medium.
- Isolate or remove relief valves, regulators, and instruments that are not rated for test pressure. Test sections, not the whole plant, where possible.
- Pressure decay must be corrected for temperature. A rising temperature can mask a leak; a falling temperature can create a false failure.
- Purging displaces air with inert gas or fuel gas until readings meet the procedure; monitor at the sample point, not at the inlet.
Worked example
A section is pressurized to 100.0 psig at 70°F. After 30 min, the gauge reads 99.5 psig at 75°F. Convert to absolute: P1 = 114.7 psia, T1 = 529.7 R; T2 = 534.7 R. Expected P2 = 114.7 × 534.7/529.7 = 115.78 psia, or 101.08 psig. The observed 99.5 psig is about 1.58 psi below the temperature-corrected expectation, so the section is leaking or has a gauge/connection error.
Traps
Comparing uncorrected gauge readings is the classic commissioning error. Another is testing with regulators in line and then blaming the regulator for a failed test. Do not sign off combustion until O2, CO, CO2, draft, and manifold pressure are recorded at high and low fire.