A 30,000 cubic meter vertical storage tank is not a bigger version of a 500 m³ tank. The shell course thickness transition, wind girth buckling check, roof pontoon balance and annular plate bearing pressure all move into a different engineering regime once capacity crosses 20,000 m³. Zhongneng Huajian's delivery of a single 30,000 m³ vertical diesel storage tank for CNOOC Zhanjiang-inside a 120-day clock-is a useful window into how a mid-size Chinese EPC-capable fabricator handles major-oil-company rigor without outsourcing the critical path.
Front-end design inputs
The client issued a datasheet with medium (diesel, density 840 kg/m³), design temperature −5 to +55 °C, seismic 7-degree, coastal wind 0.75 kPa, soil bearing 180 kPa, and code alignment to API 650 12th Ed. with GB 50128 cross-check. ZN's design team returned a 14-shell-course arrangement: bottom course 22 mm Q345R, top course 8 mm, annular plate 24 mm, with lap/butt mix optimized for plate availability. The roof was an internal floating roof with welded carbon steel pontoon and double soft seal, chosen over fixed cone roof to cut evaporation loss and meet CNOOC's VOC target.
Fabrication sequence in the 15,000 m² Shandong shop
CNC plasma cutting of shell plates with CAM nesting to keep scrap below 6 %
Four-roll bending with template check every 500 mm along the arc
Automatic submerged arc welding of longitudinal seams in flat position, circumferential seams rotated on roller stands
RT on 100 % of longitudinal seams above 10 mm, UT on plate laminations, MT on nozzle welds
Shell roundness held within 0.5 % of radius before erection
Field erection at Zhanjiang
Shell courses were assembled by jack-up method, one course at a time, with interim wind brace. Welders qualified to NB/T 47014 (equiv. ASME Sec. IX) logged each seam. Floating roof was assembled on the tank bottom before shell reached full height, then lifted with the deck-standard practice but tightly sequenced to avoid crane double-handling. Coating was split: internal epoxy primer + glass flake novolac to 450 µm DFT, external aliphatic polyurethane, blast Sa 2.5.
Acceptance evidence
Hydrostatic test used local seawater displaced to diesel-specific specific gravity correction, held 24 h with settlement observation at 8 points. Settlement differential was 6 mm against the 12 mm allowable. RT rejection rate was 1.8 %. Third-party inspector signed the mechanical completion certificate on day 118; handover on day 120.
FAQ snippet
"How long does a 30,000 m³ diesel tank take from PO to handover?" For a controlled factory like ZN with in-house rolling and SAW, 110–130 days is realistic if civil foundation is ready at month 1. The bottleneck is rarely steel-it is concrete curing and crane window.
This project is now referenced in ZN's tender pack for similar African and Middle East oil depot inquiries, alongside the 14×10,000 m³ Sinograin Hefei edible oil tank farm and the Dammam 66 m-diameter desalination water tanks.
