HFW associate Tom Morgan explains how chemical tanker operators can protect their interests in the face of damage to stainless-steel tanks from the carriage of wet process phosphoric acid
Wet process phosphoric acid (WPA) is a key component in the worldwide fertiliser industry. It is a complex mixture of phosphoric acid, corrosive compounds, such as chloride and fluoride, and other impurities such as metal oxides.
During 2017/2018, a number of chemical tanker operators faced significant damage to stainless-steel cargo tanks as a result of shipping WPA cargoes of North African origin, bound for discharge ports in India. Cargoes were shown to contain corrosive compounds above the agreed specification for carriage. Repairs and delay resulted in losses in the millions of dollars and legal proceedings.
From the shippers' point of view, the aim is to manufacture WPA to reach the P205 acid strength required by purchasers. But this creates the risk that insufficient regard is given to the concentration and impact of individual corrosive accelerators, such as fluoride and chloride, which can significantly impact stainless-steel tanks – but are of limited importance to the shippers and receivers.
The WPA cargo is loaded and blended in sub-batches to reach the required P205 strength. Throughout the process, tanker operators have noted a failure to monitor fluoride/chloride levels in the WPA. Moreover, sampling and testing during the process is only ever as good as the personnel, equipment and accreditation being used.
“In the last two years, chemical tanker operators have faced significant damage to stainless-steel cargo tanks as a result of shipping WPA cargoes”
WPA also has a propensity to be inhomogeneous in nature; corrosive accelerators can vary significantly between different batches. Pockets of high concentrations of fluorides/chlorides can corrode tanks beyond that expected by a declared homogenous specification, even if the WPA would be harmless once fully comingled. During fixture negotiations, operators should check the following:
However, some of these options may be operationally impossible, commercially prohibitive and/or there may be reliability concerns about the data provided. Moreover, there is always the risk of rogue batches of WPA.
Therefore, independent, verifiable joint sampling of the actual WPA batches loaded, complete with full chain-of-custody evidence, is invaluable. Options include:
Should damage to cargo tanks arise, operators should take immediate steps to protect their interests, particularly in relation to the sampling process. Crucially, future legal disputes will turn on the reliability and weight of each party's evidence.