Cargoes protected by additives: IBC Code 15.13

IBC Code paragraph 15.13, cargoes protected by additives, governs a monomer or other reactive cargo carried with a chemical inhibitor that suppresses polymerisation. Paragraph 15.13.3 requires the ship to be provided with a certificate of protection from the manufacturer, a requirement introduced by IMO resolution MEPC.55(33) adopted 30 October 1992. The certificate states the inhibitor, its concentration, the date it was added and the period over which it remains effective.

Some inhibitors need oxygen to function, which puts them in direct conflict with the inerting a modern chemical tanker is otherwise required to apply. Paragraph 15.13.5 resolves it: where a product contains an oxygen-dependent inhibitor and the ship is required to be inerted, inert gas shall not be applied before loading or during the voyage, but shall be applied before commencement of unloading. SOLAS regulation II-2/16.3.3 mirrors the rule for a chemical tanker and adds that only nitrogen may be used. The unified interpretation is MSC-MEPC.5/Circ.10 of 23 June 2015.

Styrene monomer inhibited with 4-tert-butylcatechol and acrylic acid inhibited with MEHQ are the standing examples, and producer cargo handling sheets set oxygen floors stricter than the Code does. The failure mode is documented: the Stolt Groenland cargo tank burst at Ulsan on 28 September 2019 from runaway styrene polymerisation, and the UK Marine Accident Investigation Branch report 9/2021 found the cargo was heated by adjacent tanks and its temperature was not monitored. The full article will cover the inhibitor chemistry, the certificate content, the monitoring regime and the depletion case.