NBIC Part 2 - In-Service Inspection of Boilers and Pressure Vessels
Purpose
Part 2 tells the inspector how to judge whether an in-service boiler or pressure vessel is safe to keep operating. It is not a repeat of the original construction inspection; the inspector is measuring change - corrosion, cracking, deformation - against the original code of construction and the item's service history.
Preparing and inspecting
- Review the data report, prior inspection reports, repair records, operating logs, and water-treatment data before looking at the item.
- External: leaks, corrosion at supports and saddles, insulation damage, foundation condition, seal integrity on relief valves, and gauge glass and low-water fuel cutoff function on boilers.
- Internal: scale, sludge, pitting, erosion, cracking, bulging, blisters, laminations, and weld condition; ultrasonic thickness readings taken at documented, repeatable locations.
- Evaluate findings against the original code (Section I, Section VIII); where the code is silent, a documented engineering evaluation - for example a fitness-for-service assessment - supports the decision.
- Set the next inspection interval from the corrosion rate and service severity, not from habit. Jurisdictions set boiler intervals; vessel programs require a documented basis.
Worked example
A vessel shell measured 0.500 in when new, 0.470 in five years ago, and 0.440 in now; minimum required thickness is 0.375 in. Corrosion rate = (0.470 − 0.440) / 5 = 0.006 in per year. Remaining life = (0.440 − 0.375) / 0.006 ≈ 10.8 years. The inspector shortens the next interval rather than using the full life, because pitting found nearby suggests localized loss faster than the general rate.
Traps
Treating remaining life as the inspection interval. Using nominal rather than measured thickness. Missing corrosion under insulation or at support contact points. Believing the in-service inspector approves repairs - that is Part 3 work.