Relocating a 1950s Tank With No Records
A 100 ft diameter x 40 ft high fixed-roof tank came with a terminal purchased in 2022. It has been out of service since 2018, is empty, and the shell manway has stood open for four years. No nameplate, drawings, material certificates, radiography records, or inspection history were transferred; the seller's operator believes it last stored diesel and was built in the 1950s. The new owner proposes to dismantle it, truck it 400 miles to a greenfield site, and put it into gasoline service (G = 0.75) for at least 20 years. The new site has a higher design wind speed than the old one and is in a region of moderate seismic demand. Steel prices are high and a new 100 ft tank has a 14 month lead time.
1. How should the proposed work be classified, and what design basis applies at the new site?
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Classification: dismantling and reconstruction. This is not a repair and not a relocation of a serviceable tank; it is a reconstruction at a new site with a new service, and it must be treated as new construction for design purposes.
Design basis at the new site:
- Shell thickness designed for the new service (G = 0.75) plus a design corrosion allowance for 20 years. The old tank's past corrosion history earns no credit.
- Wind stability and stiffening designed for the new, higher design wind speed (top wind girder, intermediate girders, anchorage).
- Seismic evaluation for the new site's ground motion and soil, including anchorage and shell stability.
- New foundation designed for the new site's soils, and in practice a new bottom and annular ring.
- New nameplate and manufacturer's data report issued by the reconstructing organization, plus a hydrostatic test at the new site.
Why it matters: a repair only has to restore the original design. A reconstruction has to demonstrate that the tank, as it will stand, meets current requirements. The wind and seismic changes alone can make a 1950s 100 ft shell uneconomic to reuse.
2. What does the missing documentation force you to do in the material and thickness evaluation?
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Without records, every assumption must go conservative and be documented:
- Unknown material: identify it (PMI, coupons, hardness) or use the most conservative allowable stress the code permits and assume the lowest joint efficiency (no radiography records means E = 0.70 rather than 1.0). Do not credit higher-strength steel on an assumption.
- Unknown original thickness: the only defensible baseline is the current UT survey. But because the tank must satisfy new-construction requirements with a full design corrosion allowance, the test is whether measured thickness minus future allowance still exceeds the new t_min for each course. Where it does not, the course is replaced; you cannot rerated your way around this when the tank is being rebuilt as new.
- No history: assume the bottom and annular ring are not reusable and plan replacement; no credit for past hydro tests. A full hydrostatic test at the new site is required and is the only practical proof of the reconstructed shell and new welds.
- Weldability: verify the existing plate chemistry and carbon equivalent before welding new seams to it; 1950s plate may need preheat or may not be suitable for the new service.
Document each assumption in the new tank file so future inspectors know the basis for E, S, and the thickness values.
3. Before committing to the move, what engineering and record-keeping judgments should the owner make?
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Feasibility screen first. Before any plate is cut, do a thickness survey, material identification, and the wind/seismic checks. A 1950s 100 ft tank moved into a higher-wind, seismic region will often require new shell courses, a new girder, or anchorage, which can consume the lead-time advantage entirely. Compare total cost (dismantling labor, transport of plate, re-erection, new bottom, new foundation, coating, hydrotest water, inspection) against a new tank, and check that the delivered plate has enough sound metal after the survey to be worth trucking.
Close out the old site properly. Empty and clean, remove sludge, gas-free before any cutting or hot work, positively isolate and blind connections, and secure openings. Because the tank sat open for four years with an unknown leak history, do a soil and groundwater assessment around the ringwall and document the result. Retain whatever records exist, even if it is only a statement that there are none.
Records for the new tank: new nameplate and data report, as-built drawings, material certificates or PMI results, WPS/PQR, welder qualifications, NDE reports, hydro test report, foundation design, and a baseline thickness survey with an inspection plan. These must be retained for the life of the tank and must travel with the tank, documented for the next owner.