Effective tank coatings are an operator’s ticket to trade. Chevron Shipping hull and coatings engineer Johnny Eliasson and Safinah Group coating consultant Michael Aamodt consider the challenges of tank coatings for challenging cargoes
The impact of developments in tank coating technology and application cannot be understated. Almost every generation of tanker design has the advantage of newly developed coatings, but this can bring challenges. In a poll during the Riviera Maritime Media webinar on tank coatings on 7 July 2020, attendees were evenly split on how tank coating developments have impacted their operations. Asked whether the useful life of tank coatings has increased over the last 5-10 years, 36% said coating lifetimes had increased, but the same number, 36%, said coating lifetimes had shortened. The other 28% of respondents found little or no change in coating lifetimes.
The first to address the concerns was Chevron Shipping’s hull & coatings engineer Johnny Eliasson, who opened proceedings. He is a chemist who entered the coatings industry in 1973. A native of Sweden, he has covered the coatings scene across Europe, the Far East and the Middle East for cargo owners, vessel operators and class. He now represents the shipowning side with Chevron Shipping in California.
Mr Eliasson offered detail on the types of coatings used on board different tanker types, noting that while much focus in the trade is placed on product tanker and chemical carrier coatings, the crude oil tanker sector offers its own set of coatings challenges. For epoxy-coated crude oil tanks, Mr Eliasson said the main concern was the temperature gradient within the cargo tank.
“The oil temperature increases deeper down the source of crude oil,” he said.
Mr Eliasson explained that different cargoes also have different impacts on tank coatings, listing EDC, ethanol, methanol, styrene, di-chloropropene, crude edible oils, binyl acetate monomer and latex among a list of cargoes that are particularly challenging for coating films.
Mr Eliasson added that stainless steel tanks can be damaged from pitting by high strength phosphoric acid. “It is important to know the source (of the cargo) to establish the suitable stainless steel for carriage,” he said, “Knowing about the cargo is very important.”
Turning to the cargo handling aspects, he commented that for critical safe and effectively handling, all the cargo characteristics during loading, during the voyage and during discharge must be known and understood: “To know is to succeed,” said Mr Eliasson.
An era of growth in the chemical seaborne trade has been characterised by an increase in vessel size, and larger vessels flex more and increase the stress on coatings, Safinah Group’s Mr Aamodt said in his presentation. The Safinah Group coating consultancy has been in existence for 21 years and prides itself on being a technical and thought leader in the area of coatings for marine, protective and yacht markets globally.
Mr Aamodt entered the coatings industry as an R&D paint chemist to develop anti-corrosive coatings. Since then, he has gained 26 years of experience in marine, protective and industrial coatings within R&D, global product management, marketing, business development, consultancy, and management in three major international coatings companies. He has specialist knowledge of marine epoxy coatings for hull, cargo hold, cargo tanks, surface technology/protection and corrosion. Prior to joining Safinah, Mr Aamodt was business development manager for a world-leading institute doing applied research in corrosion and corrosion protection.
The chemical seaborne trade has had an average 7% annual growth that has been “mainly driven by the growth of inorganic chemicals,” he said.
An increase in the methanol trade has also been a challenge, given its demanding carriage requirements, he said.
Mr Aamodt also highlighted the cleaning challenges of cargoes such as styrene, benzene, MtBE, EDC, vegetable oils and CPP which are all becoming more prevalent. From an owner/operator perspective, advantages from developing new coatings include allowing for a greater number of cargoes, fewer cargo restrictions and quicker cleaning.
“Maximising earning and minimising downtime has led to operators and owners requesting a new generation of tank coatings that better fit their operational needs,” Mr Aamodt said, noting that there also have been developments in tank cleaning techniques, with better analytical tools available to match the requirements of higher specifications from the cargoes.
Asked in a poll about their experiences with cargo tank cleaning, more than a third of webinar attendees (34%) noted it was getting more difficult, while nearly half (48%) reported cleaning difficulties were no better or worse. The remainder (18%) reported that cleaning was getting easier.
With regards to cleaning, as well as the new generation coatings, there have been developments in cleaning techniques. There are better analytical tools leading to tighter specifications for cleanliness and carriage of more high specification cargoes.
The tank coatings presentation led to some interesting questions and discussions. Mr Eliasson was asked: How do you ensure the tanks have been cleaned properly if the tanks have been painted with a high absorption paint? He replied that with high absorption paint the method to remove cargo is by diffusion. One method is continuous ventilation. Mr Aamodt added that in a porous and open structure coating like zinc silicates, there is a high degree of absorbency. But he noted that also means a high degree of de-absorbency. “Normal ventilation will desorb cargo in a relatively short time,” he said.
There is also the impact of the effective ban on using methanol as a cleaning agent. Asked what the time impact has been on cleaning after an effective ban on methanol wash, more than 70% of respondents said cleaning time required had increased by 12 hours or more, a further 15% said 1-12 hours had been added and 15% of respondents said they had seen no difference in cleaning times required.
The impact of the methanol wash ban was raised in the discussion. “Methanol wash has been the standard washing medium for tanks for years,” said Mr Aamodt, “As methanol wash is now only allowed under an inert atmosphere, it makes it very difficult, timely and costly, so the effective ban is one of the factors in the move toward low-absorption coating film, which does not need the traditional methanol wash to reach the methanol wall wash QC testing standard.” This removes the need for the methanol wash, which has the inherent dangers of handling methanol.
When questioned on the changes in coatings over the last 5 to 10 years, Mr Aamodt pointed out that while the technology has moved on, there is still a large body of knowledge surrounding the use of coatings that have been used for the last 30 years or so. “There are clear limitations based on the track record of traditional coatings,” he said. “We have seen owners and operators push past the operational capability (of modern coatings) and we have seen a surge in claims. It is very important to understand the limits of how far you can push this new technology.”
Do zinc silicate coatings absorb cargoes and swell or do cargoes diffuse within the porous matrix of zinc silicate coatings without swelling? Mr Eliasson replied that the cargo fills the voids in the coating. “These are voids, the cargo goes in and the cargo goes out. That does not cause the swelling,” he said. Mr Aamodt followed up with, "There is a pH limitation with zinc silicate coatings. As a rule of thumb, you must stay within the pH range of 6-9. Outside this range, the coating can be broken down fast, and part of that is swelling.”
The ticket to trade takeaways
Mr Eliasson: “It is extremely important to know what cargo you are carrying and what it does to the coating. Read the resistance list, find the limitations and adhere to them very carefully,” he said.
Mr Aamodt: “The selection of cargo tank technology depends on the cargo, the trading patterns, the duration, the cleaning requirements. As you move up the technology ladder, you are increasing costs, application difficulty, reducing systems mechanical flexibility and risk if cargo sequencing is done too fast. There are a lot of different challenges to take into consideration with tank coatings so we recommend shipowners/operators to a larger extent rely on independent expert advice and training to minimise such risks and assure a better fit with operational requirements,” he said.
Watch the ’Tank coatings and your ticket to trade’ webinar in our webinar library