We present a series of basic criteria for selecting the coating for a tank-lining interior.
by Nicolás F. Oriundo De la Cruz*
In the Petrochemical industry, one of the high-value processes is the storage of fuel (product) since it acts as a lung between production and transport to absorb consumption variants and also provides operational flexibility to refineries. For this, atmospheric storage tanks are used, which serve to store all kinds of chemical products from refineries, terminals, dispatch warehouses, power stations, etc.
In Latin America, commonly the design of these tanks is made under the API 650 standard that refer to the materials set by the ASTM standards and follow the safety standards given by the NFPA, Likewise, in the same standard it mentions the API 652 standard, in it they give you the general guidelines on the use of the coating for a tank interior (linings), which can give a general idea of what to use for each type of product to be stored. But this information must always be supplemented by a specialist to have a greater accuracy of the information.
Therefore, the material with which the tank was designed cannot have the expected durability if the steel is not properly protected. Then, a proper selection of the coating system (whether exterior or interior) becomes a very important point for specifiers.
Tank-lining, are coatings designed to cure at low temperatures and are applied inside and outside a tank to provide maximum protection of the substrate material against chemical attack.
Tank-Lining is often used for several purposes: to minimize evaporation, to protect the product being stored, and to control corrosion. The Lining began to be applied to steel tanks back in the 1910s. Several coating technologies began to be developed between the 30s and 60s, but by then the options were relatively small and manageable.
Since then, there have been many advances in the coatings industry driven by customers' need for better and less hazardous solutions for their asset protection needs. The downside of this progress is that asset owners face a diversity of options that would make more than one turn their heads.
For the correct design of the protective system to be used, specifiers must consider different parameters such as: service conditions (product to be stored, pH, temperature, etc.), the type of coatings used (type of polymer, number of layers, chemical resistance, etc.).
In an effort to lessen confusion, here are some general basic considerations to keep in mind when selecting a coating for a tank interior.
There are many factors to consider when choosing a coating for your project, but some considerations are more important than others.
1. Sustainability and Environment, Health and Safety (HSE)
For several years, there has been a growth in the promotion of a culture in safety, health and the environment, which is why Latin American countries have been implementing laws that help regularize the activities that are developed within their regions in this area, in order to ensure the lives of their workers, as well as to protect the environment within its national territory. And the oil and gas industry is no stranger to it, even because of the high risk involved in their activity, they are under constant scrutiny regarding their sustainability, health and safety practices.
Therefore, choosing a coating that will maximize sustainability, health and safety is a logical and very important step. Many companies in this industry have even set annual limits on volatile organic compounds (VOCs) to lessen their impact on the environment. Sustainable and safe coatings are no longer inferior and non-toxic, flash point-free, solvent-free, VOC-free and BPA-free (bisphenol A).
Currently there is talk of 100% Solid coatings, so called because there is no use of solvents in their composition, therefore, cleaning does not pose any risk to the health of applicators, while conventional products may contain solvents that can enter the body through the lungs and skin.
2. Lining Performance
The performance of the lining is another variable that we must consider when looking for the right coating for our interior of the tank, for example, the curing speed of the coating is very important to take into account. Are your storage tanks located in a wet or cold climate? Not all coatings can be cured in cold or wet conditions. Coatings in cold weather can cure at temperatures as low as -40°C (equivalent to -40°F).
What is the minimum and maximum resistance temperature of the coating? If your tanks are used for the storage of heated products, it is necessary to make sure that the coating has the proper maximum temperature range. If the coating is damaged by heat, even for a short period of time, the coating suffers permanent damage and can be easily delaminated. In the oil industry, this damage can be the result of excessive or uncontrolled use of heating; Pumping truck to circulate the oil through large heaters to raise it to get the wax, paraffin and heavier components out of the oil. In addition, during the maintenance of tanks, uncontrolled steam cleaning activity often leads to this result.
What certifications or standards must the coating meet? For example, in many cases for tanks that are going to store drinking water, one of the requirements that is requested is that they comply with NSF-standard 61, which approves the coating as a product suitable for contact with drinking water, which allows it to be applied satisfactorily in areas where it is required to protect the substrate and at the same time preserve the sanitary finish.
3. Lining durability
What is the durability of the coating? If the tank regularly experiences extreme expansion and contraction due to atmospheric conditions, then a coating with good flexibility or elongation properties is preferred. Very different case for example tanks with suspended and moving sludge, abrasion resistance would be a requirement to consider.
What is the chemical resistance of the coating being used? Has the coating been tested for a particular chemical? If the tank contents have a unique blend that has not been tested or has proprietary chemicals that are not disclosed in the MSDS, consider sending a sample to your suppliers' laboratory or requesting coated metal samples to conduct your own tests. It is important to note that even if the chemical compatibility table has a positive rating for each of the chemicals present in the liquid, the mixture can cause the properties to change and therefore affect chemical resistance.
4. Repaintability
What is the repaintability window of the coating? Some coatings have little or no repair capacity. A longer or unlimited repaintability window would drastically reduce repair costs in the future. Costs, such as abrasive jet cleaning of the entire coating and repainting the entire interior of the tank, can be avoided if attention is paid to this detail.
5. Costs and downtime
What is the cost of the total solution? The cost is per gallon and the thickness of the coating as it relates to line costs.
How long does it take to complete the work and what will it cost your organization?
This question needs to be asked when making a selection of the coating system. As we know, in many industries, such as the marine industry or the food industry, to cite a few examples, you can only do the work when the ships are in port or on the weekend when production is not happening. In addition, the requirement of surface preparation for coating drastically affects the cost of work. The cost difference between a white metal surface preparation (SSPC-SP5) and a commercial grade one (SSPC-SP6) can make or embezzle your project.
And it remains to consider the cost that the organization will have to assume for the time that it will stop producing or being in service.
To finish I want to comment that there are other factors to consider when selecting a suitable coating for your project, The list mentioned above is only general and is not exhaustive, but it can help a lot when you want to start with your project. Taking into account the points already mentioned, and working together with a professional specialist and qualified in coatings, the chances of making a better selection of your protective system will increase.
* Nicolás F. Oriundo De la Cruz
General Manager SCC Ingenieros y Consultores SAC
Chartered Chemical Engineer. CIP Level 2 N° 39046 IS BORN. NDT VT Level 2
Contact: e-mail: [email protected] - [email protected]
Cel. (511) 987816879
Lima - Peru
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