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HEAT TREATMENT
temperature of the styrene monomer during the voyage, and therefore were not aware of the increasingly dangerous situation.”
INCIDENT REPORT • MAIB’S INVESTIGATION OF THE STOLT GROENLAND EXPLOSION HIGHLIGHTS THE NEED TO PROPERLY MONITOR INHIBITED CARGOES CARRIED IN BULK A FAILURE TO appreciate the extent of heat transfer between cargo tanks, together with a lack of temperature monitoring in cargo tanks with styrene monomer, were the main causes of the catastrophic loss of containment on the chemical tanker Stolt Groenland in the port of Ulsan, South Korea on 28 September 2019, according to the report of the investigation carried out by the UK Marine Accident Investigation Branch (MAIB).
above the jetty. Two crew suffered minor injuries and 15 emergency responders were injured during firefighting efforts that lasted for more than six hours. MAIB determined that the polymerisation was initiated by elevated temperatures in the tank, caused by heat transfer from other chemical cargoes, reducing the effectiveness of the inhibitor added to the styrene. “Athough the styrene monomer had not been
AS IT UNFOLDED At the time of the incident, while Stolt Groenland (43,500 dwt, built 2009) was moored at the jetty to unload cargo, the smaller chemical tanker Bow Dalian (9,150 dwt, 2012) was moored outboard to receive cargo by ship-to-ship transfer and was already receiving nitrogen from shoreside vehicles for purging its tanks. Stolt Groenland had loaded 20 different chemical cargoes from terminals in Texas, including four tanks of hexamethylenediamene (HMD) and two of diglyceryl ether of bisphenol-A, both of which required heating during the passage to Asia. Four tanks had been discharged to barges while the tanker was anchored off Kobe; it
The immediate cause of the incident was not hard to establish: a runaway polymerisation in a cargo tank with styrene led to an overpressurisation of that tank, causing a rupture that allowed vapour to escape; this vapour found an ignition source, causing a fireball that reached the road bridge
stowed directly adjacent to heated cargo, the potential for heat transfer through intermediate tanks was not fully appreciated or assessed,” MAIB’s report says. “Critical temperature limits had been reached before the vessel berthed under the road bridge in Ulsan. The tanker’s crew did not monitor the
then proceeded to Ulsan where it discharged six tanks of adiponitrile at the Odfjell terminal before moving to the Yeompo Quay. There two tanks with Voranol were discharged to Stolt Voyager by ship-to-ship transfer. The first sign of a problem arrived with a release of vapour from the pressure/vacuum
HCB MONTHLY | SEPTEMBER 2021
