Inspection, Testing, and Quality Control
The inspection plan
An inspection and test plan (ITP) lists activities, acceptance criteria, method and hold and witness points. Hold points stop work until the inspector signs; witness points do not. Traceability runs from the mill certificate and heat number through cutting, fit-up, welding and the welder's stamp to the final test record.
Nondestructive examination methods
- Visual (VT) first and always: fit-up, root condition, profile, undercut, cleanliness.
- Penetrant testing (PT) finds surface-breaking discontinuities in non-porous materials; the surface must be clean and dry and dwell times respected.
- Magnetic particle (MT) finds surface and near-surface flaws in ferromagnetic material only.
- Ultrasonic (UT) is volumetric and needs couplant plus calibrated reference blocks.
- Radiography (RT) is volumetric; film density and image quality indicators must meet ASME Section V Article 2.
- Hardness testing and positive material identification verify properties and alloy.
Hydrostatic testing
Fill, vent all high points, pressurize in stages, hold, and inspect every joint. For Section VIII Division 1 the minimum test pressure is 1.3 × MAWP × (allowable stress at test temperature ÷ allowable stress at design temperature); Section I boilers use 1.5 × MAWP.
Worked example: test pressure
A Division 1 vessel has MAWP 1.2 MPa, and the allowable stress is the same at test and design temperature. Test pressure = 1.3 × 1.2 × 1.0 = 1.56 MPa. Before testing, confirm the metal temperature is comfortably above the minimum design metal temperature, the water chloride content is acceptable for the material, and the gauge is calibrated and in the correct range.
Traps
- Passing a joint on VT when the drawing requires RT or UT.
- Testing before all NDE is complete and accepted; repairs after the hydro mean a second test.
- Accepting a radiograph with poor density or a missing IQI, which invalidates the technique.
- Losing heat-number traceability at the cut-off saw - the material can no longer be credited to the code.