Chemical tanker cargo tank coatings (tank linings) are heavy-duty protective systems sprayed on the internal surfaces of integral cargo tanks: they isolate the steel from cargoes of very different polarity and solvent power, preventing both corrosion of the hull and contamination of the cargo by corrosion products and desorbing film components. Unlike shore tanks that hold one medium for years, a ship's tank cycles through many cargoes, so the coating must stay compatible with the owner's cargo list, the cargo-heating limit and the tank-cleaning regime — a three-way fit rather than a single chemical-resistance claim.
TL;DR — Three constraints decide selection: ① product compatibility — the maker's cargo-resistance guide works on substance × concentration × temperature, and each new fixture is checked against the previous three cargoes; ② temperature limits — novolac epoxy holds roughly 120 °C continuous, which bounds cargo heating and hot-water washing; ③ taint and repairability — epoxy absorbs and later desorbs cargo components, so film condition directly moves the next cargo's quality numbers. The mainstream build for general chemical tankers is ~70 % volume-solids novolac epoxy in 2–3 coats with post-cure; stainless steel and rubber are rival tank-wall systems, not better paints.
Key numbers
- Regulatory frame: the IBC Code distinguishes type 1 / 2 / 3 chemical tankers by the hazards of the products listed in Chapter 17 (very serious / considerable / serious hazards), as amended by MSC.460(101), adopted 14 June 2019.
- Representative product data (novolac epoxy tank coating, manufacturer page): volume solids ≈ 70 %, VOC ≈ 290 g/L (EPA method), 2–3 coats, post-cure available for higher resistance grades.
- Temperature envelope (published technical notes): ≈ 120 °C recommended continuous service, ≈ 150 °C standard grade, ≈ 200 °C short-term; full cure adds roughly +20 °C; heat-up should be staged from 80 °C with ~24 h holds; acids and alkalis accelerate high-temperature ageing.
- Absorption–desorption: epoxy films take up cargo residues and release them into the following 1–3 cargoes; blistered, broken or porous coatings retain far more; uptake rises with temperature and voyage length (West P&I guidance).
- Operational compliance: compatibility checks must cover the last three cargoes (USCG compatibility chart as a common tool); MARPOL Annex II requires pre-washing after discharge; excessive hot-water washing degrades the coating itself.
- Static accumulators: cargoes with conductivity below 50 pS/m (xylene, ultra-low-sulphur diesel, jet fuel per ISGOTT) need bonding and relaxation-time control — the insulating coating removes the steel wall as a discharge path.
Mechanism: how the barrier fails
1. Chemistry of resistance
Cresol-novolac epoxy carries more reactive groups per molecule than standard bisphenol-A resin, so the cured network is denser and richer in aromatic rings: permeation and swelling by aromatics, esters and ketones drop. The trade is brittleness — every micro-crack becomes a reservoir that holds cargo against the steel.
2. Temperature multiplies everything
Diffusion through the network rises steeply with temperature, so heated cargoes, tropical decks and steam cleaning all push uptake up; the same product can pass a resistance table cold and fail it hot. Desorption runs the same process in reverse later — the concentration gradient decides when the previous cargo 'talks' to the next one.
Specification and practice
Application, post-cure and inspection discipline
Blast-clean to Sa 2½ with a defined profile, stripe-coat welds and edges, airless-spray 2–3 coats to the specified dry film thickness, control dew point and temperature, then post-cure (heated hold or extended cure) before service — that step is what lifts the continuous-temperature grade from the 80 °C to the 120 °C class. Keep the maker's cargo-resistance guide and the INTERTANKO cleanliness standards aboard; inspect annually for discolouration, tackiness and blisters; repair only with a compatible system.
Tank-wall routes compared
| Route | Cargo family fit | Temperature | Taint & cleaning | Cost & repair |
|---|---|---|---|---|
| 316L / duplex stainless | broad organics and aqueous solutions; chloride stress-corrosion and halogenated solvents are the limits | not coating-limited; steam-tolerant | no absorption tail; fast cleaning | highest build cost (duplex higher) |
| Rubber lining | aqueous acids and alkali salts; swells in oils and solvents | ageing-limited, heat-sensitive | residue retention; one breach matters | medium; re-lining is a yard job |
| Novolac epoxy coating | fuels, aromatics, alcohols/esters/ketones per resistance guide | ~120 °C continuous after post-cure | absorption tail — ventilation & buffer cargoes | lowest of the three; spot repair, full recoat in drydock |
| Inorganic zinc (legacy tanks) | crude and selected products; attacked by acids/alkalis (amphoteric zinc) | heat-tolerant but narrow chemical window | porous surface holds residues (high-FFA oils case) | declining; rare on newbuilds |
FAQ
Q1: Why is there no all-cargo coating?
Resistance is a function of substance × concentration × temperature × contact time. Every system has failure boundaries, so the real cargo list is the intersection of the Certificate of Fitness and the maker's resistance table.
Q2: Why check the previous three cargoes?
The desorption tail can persist for one to three voyages: absorbed components keep leaving the film after loading. Checking only the immediate last cargo systematically underestimates contamination risk.
Q3: What does post-cure actually change?
It completes crosslinking: fewer network defects, roughly +20 °C on the service ceiling, lower swelling and a faster-tapering desorption tail. A tank handed over without post-cure should stay within ambient-temperature grades.
Q4: Is hotter tank cleaning better?
No. Excess hot water accelerates coating degeneration — explicit in West P&I guidance — and raises uptake. Respect the stated wash-temperature ceiling and let detergents and mechanical action handle stubborn residues.
Q5: How to start a B2B specification project?
Send the Certificate of Fitness cargo list, heating regimes, trade pattern and current tank condition; expect a resistance-table audit, damage grading and a repair-compatible specification. Supply on EXW/FOB terms with a technical agreement covering trial panels.
Last updated: 2026-09-28
Sources: IMO IBC Code portal page & MSC.460(101) amendment (2019); West P&I bulletin “Cargo Tank Cleaning and Preparation Onboard Tankers” (2026); AkzoNobel International Interline 994 product page; published novolac heat-resistance notes (2026); ISGOTT conductivity criterion.
Kexin New Materials (Guangdong) Co., Ltd.