Lining is typically used for several purposes: to minimize evaporation, to protect the product being stored and to control corrosion. Lining started to be applied to steel tanks in the mid to late 1910s. Various lining technologies were developed in the 30s to 60s, but the choices 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 to their asset protection needs. The downside of this progress is that the asset owners are faced with a mountain of choices that would make anyone’s head spin. In an effort to decrease the confusion, here are some general considerations when considering an internal tank lining.
1. Sustainability and Environmental, Health and Safety (EHS)
Industries such as the oil and gas industry are under constant scrutiny regarding their sustainability, health and safety practices. By choosing a liner that will maximize on sustainability, health and safety is a logical step. Many companies in these areas have set yearly volatile organic compound (VOC) limits to decrease their impact on the environment. Sustainable and safe coatings are no longer inferior and are non-toxic, flashpoint-free, solvent-free, VOC-free and BPA-free. Because there is no use of solvents in the coatings, cleanup does not pose any health risks to the applicators, whereas conventional products may contain solvents that can enter the body through the lungs and skin.
2. Lining Performance
Curing rate is a very important consideration. Are your tanks located in a humid or cold climate? Not all coatings can cure in cold or humid conditions. Cold-weather coatings can cure in temperatures as low as -40ºF (-40ºC).
What is the minimum and maximum temperature of the lining? If your tanks are used for storing heated materials, you need to make sure that the coating has the appropriate maximum temperature range. If the lining is damaged by heat, even for a short period of time, the coating becomes permanently damaged and will delaminate easily. In the oil field, this damage can result from excessive or unmonitored use of the heating/pumping truck to circulate the oil through big heaters to raise it to get the waxes/paraffin and heavier oil components out. Also, unmonitored steam cleaning activity often leads to this result.
What certifications are required for the applications? For example, potable water applications require an NSF-61 rating.
3. Lining Durability
What is the durability of the coating? If the tank is regularly being moved, or if it experiences extreme expansion and contraction due to atmospheric conditions, then a lining with good flexibility or elongation properties is preferred. For mud tanks collecting or moving slurry, abrasion resistance is a requirement.
What is the chemical resistance of the liner being used? Has the lining been tested for a particular chemical? If the contents of the tank have a unique mixture that hasn’t been tested or has proprietary chemicals that are not disclosed in the material safety data sheet (MSDS), consider sending a sample to your vendors’ lab or requesting liner-coated metal samples to conduct your own tests. It’s important to note that even if the chemical compatibility chart has a positive rating for each of the chemicals present in your fluid, the mixture may cause the properties to change and therefore affect the chemical resistance. (For more on selecting the proper lining, read Choosing a Fit-for-Service Lining System for Process Vessels.)
What is the repairability window for the lining? Some linings have little to no repairability. A longer or infinite repairability window would drastically reduce the costs of future repairs. Costs, such as abrasive blasting of the entire coating and recoating the entire tank, can be avoided by paying attention to this detail.
5 Cost and Downtime
What is the cost of the total solution? The cost is per gallon and coating thickness as it is related to liner costs. (Learn how to measure coating thickness in the article 7 Methods of Coating Thickness Measurement.)
How long will the job take to complete and what will that cost your organization? In the marine or food industry, you can only conduct the work when the ships are in port or on the weekend when production is not occurring. Also, the surface preparation requirement for the lining drastically affects the cost of the job. The difference in cost between a NACE 1 and NACE 3 standard can make or break your project.
There are many factors to consider when selecting a suitable liner for your project. The list above is a general one and is not exhaustive. By considering the points above and working with a qualified coating professional, your chances of making the best selection will increase.