Decommissioning, Relocation, and Records
End of life, new life, and the paper trail
Decommissioning starts with making the tank safe: empty, drain, isolate with blinds and lockout, clean sludge per API 2015/2016, gas-free and vent, and control entry. A tank that is idle but retained is not a closed case - corrosion continues, cathodic protection must be maintained, and vents and seals still need attention.
Dismantling requires a plan, cold cutting or controlled hot work only after cleaning and testing, and disciplined marking of shell plates by course and orientation so the tank can be re-erected with the original plate arrangement. Each shell seam loses a strip of plate to the old weld and its heat-affected zone, so thickness must be rechecked against the required t_min before plates are re-used. Before and during removal, examine the bottom for evidence of leakage and assess the ground beneath for contamination.
Relocation/reconstruction is not a bolt-together exercise: the tank is re-evaluated for wind, seismic, brittle fracture, and current service; all new welds meet API 650 quality with radiography; a full hydrostatic test is performed; a new settlement survey is taken; and a new nameplate identifies the reconstruction.
Records are the other half of this domain. The owner/operator keeps, for the life of the tank: original construction drawings and specifications, material certifications, welding procedures and qualifications, radiographs and other NDE reports, hydrostatic test records, all inspection reports and thickness data, repair and alteration records, and the calculations behind inspection intervals. These must be available to the inspector; when a tank is relocated, the file travels with it.
Traps: assuming an old nameplate and old design basis survive reconstruction; thinking no records are needed because "the tank is old"; skipping the post-reconstruction hydro test.
Rule of thumb: if you cannot produce the original specific gravity, material, and thickness, the tank must be re-quantified by UT and material testing before it is repaired or moved.