Testing cargo tank coatings provides answers on maritime chemical service
According to Donald J. Keehan, chairman, Advanced Polymer Coatings (APC), of the USA, the industry often turns to various types of testing to solve the chemical cargo mystery before a chemical is even carried.
Questions cover important parameters such as: how to select the best type of cargo tank coating/material to handle a specific chemical; how to plan out profitable trade cycles; how to avoid product contamination; and how to effectively clean the cargo tanks.
“Can my vessel carry this particular chemical cargo?” This query is asked daily, as thousands of different chemicals, including acids, caustics, and solvents are carried. Marine transport continues to be the most economical method to move large quantities of bulk chemical cargoes. There are many different types and sizes of vessels that transport liquid cargoes. The overriding concern to ship owners, operators, chemical companies, and maritime regulators is the safe carriage of these cargoes, many which are deemed hazardous.
There are various types of cargo tank coatings or tank materials specified for chemical tanker service, which include either a) cargo tanks fabricated of stainless steel, or b) carbon steel tanks that are lined with a coating such as a phenolic epoxy, inorganic zinc, or MarineLine 784 polymer coating from APC. Each of these approaches offers different benefits for certain chemicals, with limitations.
Fabricating tanks of stainless steel has a high initial cost of construction. And the ongoing cost to maintain tank conditions through passivation is expensive and dangerous, yet necessary at various points throughout the cargo tank’s life cycle. While stainless steel can handle a number of chemicals, it has inherent problems with chloride attack, thus making cleaning the tanks costly because fresh water or treated seawater is needed. Stainless steel also has problems with chlorides that limit its ability to carry certain cargoes.
Next, conventional coatings such as inorganic zincs and phenolic epoxies also have limitations carrying certain cargoes and have extensive cleaning requirements. These limitations are based upon their chemical structure that inherently allows some cargo absorption.
For instance, traditional cleaning chemicals can destroy zinc when cleaning from a dyed gasoline, gasoil, or vegetable oil to Methanol or MEG. In addition it takes an extensive amount of time and effort to thoroughly clean the tanks.
Epoxy coatings have very high absorption properties, especially if carrying a product such as Methanol, and have many restrictions for cleaning and cargo loading. For instance Methanol is not normally loaded after carriage of styrene monomer or EDC for three cargo cycles in an epoxy coated tank. In addition there are strong cargo restrictions on the carriage of edible oils and other sensitive chemicals.
APC says its MarineLine 784 coating, based on a unique tightly knit polymer formulation, withstands all IMO approved chemical cargoes, providing high performance and a wide breadth of cargo-carrying capability for use in chemical and product carriers, which the company says is a key reason why the product has become a standard in the industry.
For many years, APC has continually tested MarineLine 784 against a wide range of standard chemicals, and also against new emerging chemicals based on new formulations. To date, thousands of chemicals have been reviewed, and these are reported on the APC website under ‘APC Cargo/Chemical Resistance Guide’.
APC maintains an extensive laboratory and staff for testing and analysis at its headquarters. Some customers, potential charterers, and chemical companies may ask to have particular chemicals lab-tested against the MarineLine 784 coating to see how the coating withstands chemical attack and corrosion, while ensuring product purity. Requests to APC for testing may come about as the ship owner is currently carrying a certain chemical in its MarineLine 784 coated tanks and wants to monitor particular performance aspects. Or he may be considering carrying a new chemical at a future date and needs to determine if it can be suitably handled, and wants to assure the customer of this capability.
Some chemical producers will send specific liquid substances to APC to run a battery of tests. These testing services are typically provided at no cost by APC, in an effort to work in partnership with customers. APC seeks to find out just how well MarineLine 784 works, and if testing is successful, the chemicals are added to the approved ‘APC Cargo/Chemical Resistance Guide.’ Key analytical tests are performed at APC according to DIN standards, and/or a combination of customer-focused fields of study. These can include:
- Gas Chromatography
- Gas Chromatography Mass Spectroscopy
- Fourier Transform Infrared Spectroscopy
- Differential Scanning Calorimetry
- Gel Permeation Chromatography
- Physical Properties Testing
- Gardner Impact
- Chemical Immersion at various temperatures
- Water Baths
- Oil Baths
- Atlas Test Cell
- Wet Properties & QA Testing
- Field testing
In some instances, shipowners or operators require actual field testing to further check the performance of MarineLine 784 before employing a full-ship cargo tank coating. Typically this will involve one or several new cargo tanks that are coated with MarineLine 784, or a refurbishing of the customer’s existing tanks that have a different coating. For refurbishing, the tanks are grit-blasted clean and re-coated with MarineLine 784. In-the-field testing is especially important for fleets of chemical or product tankers looking to upgrade tank cargo capabilities to carry more versatile and hazardous cargos, but who want to first test the MarineLine 784 coating to ensure it delivers on its capabilities. Close monitoring is conducted at each stage of the testing and with follow up cleanings.
In a more unusual field test, Keehan relates the story of one shipowner who wanted to pick up a charter to carry cognac. The cognac producer asked to test the MarineLine coating to ensure product purity before agreeing to the charter. A full load of cognac was loaded in a cargo tank lined with MarineLine. Prior to leaving port, the company’s cognac ‘taste tester’ sampled the cognac in the tank. Then the ship left for its overseas voyage and landed at its new port where the company’s taste tester had already flown. Once the cargo tank was opened, he again tasted the cognac and certified that it had remained pure, which led to future cognac charters for the shipowner.
As can be expected, all the major chemical companies all have vast in-house testing facilities and can request MarineLine 784 coated samples that can be used in a wide range of performance tests including immersion service at various time lengths. A valuable resource for the industry is a number of outside testing laboratories that provide independent analysis of how coatings can handle the carriage of various liquid cargoes for chemical resistance, cargo absorption, and ease of cleanability.
One independent testing story that Keehan cites was a potential customer who wanted to test another of APC’s coatings — ChemLine 784, a high performance lining for industrial applications — to check if it could carry chloro acetylic chloride at 55° C. The ChemLine® 784 application was for lining product tankers (for road and rail transport) that would carry this particular chemical throughout Europe.
The Berlin- based independent organization, Federal Institute for Materials Research and Testing (BAM), conduced a series of tests related to the evaluation of corrosion resistance of delivered specimens coated with ChemLine 784 according to DIN 50905 and DIN 6601, and of possible changes of coating properties according DIN EN ISO 2178, DIN ISO 4624 and following DIN EN ISO 10308. The various exposure test results did not show any significant corrosion effects or corrosion-relevant changes of the coating, so this helped the customer decide the coating would perform to the standards required.
To date, a number of product tankers are now handling this service in Europe with ChemLine 784, due to this successful testing report.
In another example of independent testing, this time focused on maritime cargo tank cleaning of various coatings and stainless steel, the Federation of Oils, Seeds and Fats Associations (FOSFA), the professional entity concerned exclusively with the world trade in oilseeds, oils and fats, hired British-based MarinSpec Associates, an independent consultancy group with a deep knowledge and understanding of cargo tank coatings and tank cleaning procedures, to investigate the influence of tank cleaning on the transmission of chemical cargoes retained in organic cargo tank coatings into vegetable oil cargoes. That report concluded that the coating/material that performed the best (transmitted the lowest concentration of the chemical cargoes into the vegetable oils) was MarineLine 784.
Based on these results, APC asked MarinSpec Associates to conduct further testing along this line, with the primary objective to compare the transmission characteristics of MarineLine 784 against a typical zinc silicate coating, a typical epoxy phenolic coating, and stainless steel, under the international industry rules for the carriage of edible oils in ship's cargo tanks. Results showed MarineLine performed as well as stainless steel in ensuring edible oil purity when tested respectively with styrene monomer and EDC as last immediate cargoes. And MarineLine outperformed phenolic epoxy and zinc silicate coatings in these applications.
Thus, an independent testing company provided a valuable service to the industry with research that showed shipowners there is a whole new market for chemical and product tankers that want to carry vegetable oils and edible oils with MarineLine 784 coated cargo tanks without having to employ costly stainless steel tanks or other coatings.
Many resources are available to the ship owner and operator, charterer, or chemical company wishing to find the answers for cargo tank performance. With proper testing, the best choices can be determined to ensure the safe carriage of bulk liquid cargoes by maritime vessels and other transport vehicles, whether it is assessing how a coating will handle a particular trade, monitoring how cleaning procedures and chemicals impact tank performance, and other key factors.
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