T11 is the global workhorse of the ISO tank fleet. The IMDG Code Chapter 6.7 assigns T11 to roughly 1,000 UN-numbered chemicals across Classes 3, 6.1, 8, and 9, plus the substantial population of food-grade and water cargoes that travel in the same physical equipment. Min test pressure 6 bar, maximum allowable working pressure 4 bar, 6 mm reference-steel shell (about 4.18 mm in 316L stainless via the Lloyd’s formula in IMDG 6.7.2.4), bottom outlet allowed, normal pressure-relief valve. Of the 882,023 ISO tanks in service on 1 January 2025 per the ITCO Annual Market Report, the great majority are T11 builds.
What T11 is built for
T11 carries the broad middle of the chemical lane: alcohols (methanol UN 1230, ethanol UN 1170), ketones (acetone UN 1090, MEK UN 1193), aromatic solvents (toluene UN 1294, xylene UN 1307), glycols (MEG UN 3082, DEG, propylene glycol), aniline, formaldehyde, glacial acetic acid (heated, 316L-compatible at temperatures above the 16.6 deg C melting point), formic acid, hydrogen peroxide in dedicated builds up to 60%, chloroform, acrylic acid stabilised, molten phenol. Most Class 3 PG II and PG III flammables ride T11. Most Class 8 PG II and PG III corrosives ride T11 unless metallurgy demands a lining. The IMDG Dangerous Goods List Column 13 is the authoritative cargo-to-T-code lookup for any specific UN entry.
T11 is also the fleet base for food-grade and pharma-grade builds. Stolt Tank Containers operates the world’s largest food-grade fleet, with dedicated equipment that never carries chemical cargo. Hillebrand-Gori specialises in wine, spirits, and beer in T11-spec tanks polished and certified for food contact (FDA 21 CFR 177, EU 1935/2004, Kosher, Halal). Pharma-grade T11s with mirror-polished interiors (Ra under 0.4 micrometres) and CIP / SIP fittings carry pharma intermediates, glycerine USP, propylene glycol USP, and IPA pharma-grade.
Construction and materials
A standard T11 is a 316L stainless cylinder dished at both ends, mounted in a 1CC ISO 668 frame, insulated with 50 to 100 mm of polyurethane foam under aluminium or GRP cladding. Top fittings: DN500 manlid (bolted, hinged, or low-profile), 3 inch top discharge or loading flange, 1.5 inch air-inlet ball valve, spring-loaded PRV set 4.0 to 4.4 bar with vacuum-relief at minus 0.21 bar, sample valve, thermometer well. Bottom fittings follow the IMDG three-closure rule: a 3 inch internal foot valve at 45 degrees with cable-operated emergency closure, a butterfly or ball secondary valve, and a flanged outlet with dust cap and PTFE-gasketed chain. Foot-valve brands you will see on a quality fleet: Perolo, Fort Vale, Pelican Worldwide, Guard Europe.
Insulation lets a T11 hold elevated-temperature cargoes such as glacial acetic acid above its 16.6 deg C freezing point and phenol above its 41 deg C melting point. Steam coils (8 to 12 longitudinal stainless 316 coils, 6.5 to 13 m2 of heating area, 1 inch BSP inlet and outlet) raise the operating envelope to about 130 deg C. Higher-temperature builds run to 160 deg C. The vacuum relief at minus 0.21 bar protects the shell against collapse during cool-down or pump discharge.
When T11 is the right choice
T11 is the right tank when the assigned T-code from IMDG DGL Column 13 is T11 or anything weaker (T1 through T10), because the substitution rule in IMDG 4.2.5.2.5 lets a weaker-coded cargo ride a stronger-coded tank. It is the right tank when shell metallurgy is satisfied by 316L stainless (most non-aggressive Class 3 and Class 8 PG II/III chemistries), when the cargo density allows a fill above 80% of tank volume at the weight cap (the surge-floor rule of IMDG 4.2.1.9.1.1), and when shipper logistics prefer the largest fleet pool with the shortest lead time and lowest unit cost.
When T11 is the wrong choice
T11 is the wrong choice for the high-hazard end of the chemical lane. PG I corrosives, the toxics-by-inhalation of Class 6.1 PG I/II, and aggressive concentrated acids that attack 316L (anhydrous HF, fuming sulphuric, oleum, fuming nitric) require T14 or stronger and either a lined build or specialist alloy clad. It is also the wrong choice for dense cargoes where the mass cap lands the fill in the IMDG 20% to 80% surge band: 98% sulphuric acid (SG 1.84) loaded into a 24,000 L T11 hits the weight cap at 17,400 L, which is 72.5% fill, and the IMDG surge rule rejects it. Pick a smaller-volume T14 (around 21,000 L) so the same mass loads above 80%, or specify a baffled T11 build.
A specific failure mode
A US Gulf importer books 32 tonnes of monoethylene glycol from Yangshan to Houston in a stock T11 with no recent cleaning certificate from the operator. Cargo arrives off-spec on iron content. Investigation: the prior cargo was an iron-bearing salt brine, and the EFTCO cleaning document (ECD) was issued by a depot that does not run a food-grade line. The fix on the next booking: insist on a dedicated MEG fleet from an operator that runs a food-grade ECD, or a fresh wash to the EFTCO P15 CIP standard with a documented riboflavin or TOC swab before loading. Always require the ECD to be under 30 days old and to name the prior cargo.
How to verify a T11 booking
Pre-loading inspection at the port should cover the CSC plate (within 30 months), the 5-year hydraulic test plate, the 2.5-year intermediate inspection plate, the EFTCO ECD covering the cleaning steps performed since the last cargo, the manlid seal, the placards (UN four-digit number, hazard label, marine pollutant where required, elevated-temperature symbol where applicable, ADR orange panels for inland transit), and the lining condition where the build is lined. Surveyors who perform this work commercially: SGS, Bureau Veritas, Intertek, Cotecna, Saybolt.