T7 is the IMDG Code Chapter 6.7 portable tank instruction for Class 3 packing-group II and III flammables and certain Class 8 corrosives. Min test pressure 4 bar, MAWP 2.65 bar, 6 mm reference-steel shell, bottom outlet permitted for solids only (liquid bottom outlets prohibited), normal pressure-relief valve. The defining build on the China-Australia chemical lane: a T7 carbon-steel shell with a 16 to 20 mm rotomoulded LDPE / LLDPE liner carrying hydrochloric acid 35%, sodium hydroxide 50%, sodium hypochlorite 10 to 15%, and phosphoric acid 85%.
What T7 is built for
The IMDG Dangerous Goods List assigns T7 to a substantial portion of Class 3 PG II/III flammables and to Class 8 PG II/III corrosives where bottom-outlet failure under fire conditions is undesirable. In Chinese export practice T7 is the standard frame for PE-lined corrosive tanks shipped to Vietnam, Indonesia, Australia, and Africa. Hubei Dongrunze, Henan Lishixin, Tianjin Longteng, and the broader cluster of Chinese tank manufacturers build the lined-T7 fleet that moves caustic and hydrochloric on multi-thousand-tonne monthly volumes.
Construction and materials
Two routes. Route one: 316L stainless cylinder, used for Class 3 cargoes that don’t need a lining and where the operator wants substitution-rule flexibility into the T11 envelope. Route two: carbon-steel Q345R shell with a 16 to 20 mm LDPE / LLDPE rotomoulded liner. The liner is fabricated as a single rotomoulded part inside the steel shell, with welded fittings at the manlid and outlet. Liner life on caustic service runs about 5 to 8 years depending on cargo temperature and cleaning aggression; liners do not survive mechanical cleaning with high-pressure water jets.
Tare on a lined T7 runs 5,200 to 5,500 kg (vs about 4,000 kg for an unlined stainless T11). The extra mass is the lining itself plus the heavier carbon-steel shell. Effective capacity drops to 18,000 to 22,000 L because the liner occupies internal volume.
When T7 is the right choice
T7 is the right tank for the China-Australia HCl 35% lane, the China-Vietnam caustic 50% lane, and the China-Indonesia sodium hypochlorite lane. The lined-T7 build is a workhorse on these routes specifically because the fleet exists in volume at Chinese loading ports, the per-tonne economics are competitive, and the chemistry compatibility profile is well-understood. Liner life is treated as part of the operating cost rather than a one-time issue.
When T7 is the wrong choice
T7 is the wrong tank for any cargo IMDG DGL Column 13 assigns to T8 through T22 (PG I corrosives, high-hazard Class 6.1 toxics). It is also the wrong tank for cargoes that attack LDPE: concentrated sulphuric acid above 75% rapidly destroys the liner, ozone generates pinholes, hot caustic above 60 deg C accelerates degradation. The decision tree for HCl: 35% in T7 PE-lined is fine; concentrated 70% HCl is not common in commercial trade but would require PTFE.
How to verify a T7 lined booking
Pre-loading inspection covers the standard plate stack (CSC, 5-year, 2.5-year, EFTCO ECD) plus a lining-condition check. Visual inspection of the liner through the manlid opening looks for blistering, delamination from the steel substrate, or pinholes (a spark test is sometimes used after particularly aggressive cleaning). Liner certificate from the manufacturer (Marflex, AGRU, or the Chinese rotomoulding houses) lists installation date, material grade, and re-test history. A 7 to 10-year-old lined T7 with a serviced liner is normal; a 12-year-old liner with unknown service history is a flag.