The offshore DNV 2.7-1 ISO tank (now DNV-ST-E271, formerly DNV 2.7-1, paired with EN 12079) is the crane-lifted rig-supply variant of the ISO tank fleet. The build serves oil-and-gas offshore platforms, wind installations, and supply-vessel operations where the equipment is craned between vessel deck and platform deck rather than handled by twist-lock. Withstands 30-deg static tilt without overturning, dynamic shock loads from offshore lifting, and crash-frame impacts on rig decks. Annual recertification by a DNV-authorised inspection body, more frequent than the 2.5-year cycle for standard ISO tanks.
What offshore DNV is built for
The cargo population is rig-supply chemistry: drilling fluids, completion fluids, well-treatment chemicals, drilling-mud components. Specific cargoes vary by service: water-based muds, oil-based muds, brines (calcium chloride, sodium bromide), corrosion inhibitors, surfactants. The volumes are smaller than standard ISO-tank lots (1,000 to 10,000 L per tank, with 4,542 L being the workhorse 1,000-gallon T11 build in the 21H1 beam-frame configuration).
Construction and materials
316L stainless cylinder for chemical compatibility, mounted in a heavier offshore-rated frame. The frame uses Cor-Ten SPA-H or Q345D/E36 weathering steel painted with marine-grade epoxy plus polyurethane top-coat (acid, alkali, UV, salt-spray resistant). Lifting pad-eyes welded to the frame at the four upper corners for crane attachment. Side fork pockets fitted in addition to bottom corner castings (offshore tanks are sometimes handled by fork-lift on rig decks). Bumper bars at the corners protect the cylinder from impact damage during transfer.
The 21H1 beam-frame configuration is the workhorse offshore design: a 10 ft frame with a 4,542 L (1,000-gallon) T11-spec stainless cylinder mounted in a Cor-Ten beam frame with crash protection. Capacity ranges from 1,000 L for small specialty cargoes to 10,000 L for higher-volume drilling chemistry.
Sub-types proliferate: offshore reefers (Cargostore brand), explosion-proof Zone 2 reefers (ATEX certified), offshore cement and silo tanks, offshore mud skips, offshore baskets for non-tank cargo. Manufacturers: Sure Tank (Ireland) and Suretank are the dominant European specialists; M Engineering and ACE Containers serve other markets; CIMC has an offshore line.
When offshore DNV is the right choice
Offshore DNV is the right tank for any cargo movement that involves crane lifting at one or both ends of the route. Rig-supply chemistry, marine-construction chemicals, and offshore-wind support cargoes ride this fleet. The annual recertification cost is part of the fleet operating model.
When offshore DNV is the wrong choice
Offshore DNV is the wrong tank for standard onshore-onshore intermodal traffic. The heavier frame and the smaller-volume optimisation make per-tonne economics worse than a standard ISO 1CC tank for high-volume bulk-liquid lanes. The annual recertification is wasted regulatory cost on a tank that never sees offshore service.
How an offshore DNV booking is verified
Pre-loading inspection covers the standard ISO-tank plate stack (CSC, 5-year, 2.5-year) plus the DNV-ST-E271 / EN 12079 / DNVGL annual recertification certificate. The lifting pad-eyes are visually inspected for crack indications, and the frame’s structural integrity is verified for the rated lift mass. For DG cargoes the standard IMDG / CSC / UN portable tank certifications apply alongside the offshore certifications.