DOSSIER

 

Cargo claims related to tank coating


An increase in insurance claims related to tank coatings has led IUMI’s Joint Hull Committee to form a subcommittee to investigate. Surveyor Paul Hill explained the issues

There has been an increase in insurance claims, or ‘losses’, relating to tank coatings, said Paul Hill, Managing Director, Marine at consultancy AqualisBraemar.

He was speaking at the International Union of Marine Insurance (IUMI) Annual Meeting held online during September.

In these claims, an important question for insurers, and shipowners, is whether the shipowner could be considered “grossly negligent”, and so themselves to blame for any damage to the cargo, because of how the coating was applied or looked after, he said.

Mr Hill is a member of the IUMI Ocean Hull committee, which recently formed a subcommittee to investigate tank coatings losses, and produce guidance notes, he said.


Coating outline

Most tankers have tanks made with mild steel and a coating. Another option is stainless steel but that is “probably too expensive for a lot of shipowners,” he said.

The coating on mild steel is commonly referred to a “paint” – but this can be a misleading term. “Paint is what we paint our living rooms, cars with. What we use on ships is a coating system, far more sophisticated products, a sophisticated engineering system,” he said.

The coating prevents rust forming on the steel, but broken down coating can itself contaminate the cargo.

Ships are traditionally coated with epoxy coatings, which are usually applied in two parts. Types include pure epoxy, polyisocyanate epoxy and phenotic epoxy. “The data shows that most ships built in the last 10 years have this sort of coating.”

It is the “cross link density” between molecules in the coating which provides the resistance to cargoes. This is lowest for pure epoxy and highest for phenotic epoxy.

There are also “high end coatings,” including siloxirane, biomodal, and solvoxirane, sold by companies such as Marine Line, International Paints and Jotun, he said.

“They have low cargo absorption, they don’t need so much cleaning and drying,” he said.

“They have extended chemical resistance.”

It means they can carry a greater variety of cargoes, and there are less restrictions on which cargo can follow another one. It also means that the coating is easier to clean and dries faster after cleaning.

However the coatings can require more surface preparation before they are applied, and have stricter humidity and temperature restrictions when they are applied.

Shipowners normally only use an expensive coating when the specific cargo they are planning for the vessel would require it, he said.

Coating manufacturers provide lists of products that a tanker with their coating is able to carry, put together from laboratory testing.


Application and maintenance

Before a coating is applied, steel surface preparation is of “paramount importance”. The mild steel needs to be blasted to a certain standard. It must be clean but not totally smooth, because some roughness is required to allow the coating to bond to the steel, he said.

After the application, the coating may need curing. This is slightly different to drying, it is about the solvent being evaporated. The curing is considered complete when the coating reaches its “optimum hardness,” which can be weeks later. Heating can make the process go faster.

A shipyard will provide the shipowner with a technical file with records of all aspects of the coating process. This file will be consulted if there is any investigation later.

During operation, the coating needs to be cleaned when the cargo is changed, usually with high pressure, high temperature water.

To know how a coating needs to be cleaned, and how much time is needed to dry, shipping companies could refer to sources such as the coating specification, instructions from charterers, or tank cleaning guides such as Dr Verwey, he said.


Common problems

Coating problems can occur before delivery of the ship, in the first year of service, and later on during life.

The most common problem seen before delivery of the ship, according to Mr Hill’s experience as a surveyor, is “delamination” of the coating (layers of the coating separating).

During the first year of service, the most common problem is blistering and cracking.

After 1-10 years you might see ‘cathodic disbondment’, which means loss of adhesion between the coating and metal due to a cathodic reduction reaction at the interface of coating, and delamination, described above.

After 10-25 years of service you see the above plus “stress concentration”, cracking as the coating ages.

Much of this is linked to poor surface preparation right at the outset, he said. There can also be problems from an inconsistent coating application. If the vessel is in a part of the world with extreme temperature and humidity conditions, “they need to be managed properly”.

In service, problems arise from poor tank cleaning methods. “The procedures I’ve described need to be followed. If they’re not followed this can result in premature coating breakdown.” For example, companies not following washing or drying procedures, carrying cargoes which are not compatible with the coating, or having an “incorrect” cargo cycling sequence.

Another source of problems is poor maintenance by crew. “The crew do their best as always, if there are isolated areas of breakdown, blistering, the crew will get the tin of paint and patch it up. That needs to be done properly.”

It is the owner’s responsibility to select the right vessel design, the right coating product, and ensure correct application of the coating. “It is prudent for owners to have their own paint inspector, or a superintendent with that experience,” he said.

If a cargo owner thinks their cargo has been contaminated, they submit a claim, and a surveyor is sent to make an assessment. The surveyor will look at the coating technical file, records of the cleaning operation, and the shipowner’s procedures.

Shipowners are sometimes reluctant to hand over files to surveyors acting for others. But once they have done this, this audit is “relatively easy” and something which could be done remotely, he said.

“Even the most experienced operators don’t follow the procedures totally, there are shortcuts taken,” he said.

 

 

 

 

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