The life, safety, and reliability of above ground storage tanks can be greatly extended through the use of protective industrial coatings. Selecting the wrong coating or failing to use coatings entirely can result in corrosion, leading to ruptures or even collapses that can be disastrous.
An additional challenge in selecting the right protective tank coating is that many of today’s above ground storage tanks are used for broad service to accommodate a wide range of ever-changing needs. For example, a tank used for process water may be required to hold alkylate in 18 months. Will the original coating hold up under these new conditions, or will it require hefty refurbishing and re-coating expenses and downtime?
In this post, we’ll explain the impact of corrosion on above ground storage tanks and its impact on their availability and life-time costs.
Above-Ground Storage Tanks and Tank Life Expectancy
Most above-ground storage tanks are constructed of carbon steel. Tank life expectancy is 25-40 years. If no coatings are used, corrosion on floors and heat-affected zone (HAZ) regions is normally noticed within 15 years of tank commissioning. Petrochemical products containing chlorides and sulfates can be particularly corrosive, often resulting in aggressive corrosion rates leading to premature failure and potential damage to the surrounding environment.
Tanks are normally set on a three-year inspection cycle per the guidelines of the American Petroleum Institute (API). However, many tank owners try to extend the inspection cycle much longer — often to even more than 10 years.
Depending on the tank contents, internal inspection may be extended to every five years if reliability-centered maintenance practices are being followed. If you select a coating that can withstand all intended exposures over extended service cycles, you can possibly extend inspections cycles and mitigate potential corrosion.
Taking an above ground tank out of service is a complicated and costly exercise. The period of time that the tank is out of service means that facility has lost capacity until the tank has been inspected and recommissioned. These factors should be a primary consideration when you evaluate coatings as a means of protecting tank internals from the effects of corrosion.
Tank Maintenance / Inspection
There are a number of discrete steps used to inspect and address tank repairs as shown below:
Figure 1: AST Life Cycle
Associated Costs and Commercial Repercussions
Most of these tank maintenance, inspection, and refurbishing steps have significant associated costs to the facility or tank farm owner:
Figure 2: Standard Tank Refurbishing Steps & Costs
| PROCESS | ESTIMATED EXPENSE |
| Empty tank / drain pipeline | $25,000 |
| Isolate the tank | $5,000 |
| Air quality test | $2,500 |
| Tank clean/degas | $75,000 |
| Waste sludge disposal | $20,000 |
| Re-test air | $2,500 |
| Inspection | $30,000 |
| Mechanical repairs | $75,000 |
| SUBTOTAL | $235,000 |
| Coating (Labor & Product) | $228,000 |
| TOTAL | $463,000 |
When a tank has been decommissioned for inspection and repair, would be the ideal time to apply protective coatings suited for the broadest range of exposures intended for that tank. The incremental cost of the coating application can play an enormous role in preventing corrosion and metal loss leading to spills. Failure to apply a coating will likely result in continued costly mechanical repairs and increased spillage risks.
Tank Capacity Issues
Beyond a financial impact, re-coating tanks for new applications has a severe impact on capacity management for tank farm owners.
There are an estimated 2,200 terminal facilities worldwide with above ground storage tanks (AST) capacity for 2,750,000,000 M3 (API).
- There are roughly 60 days of buffer capacity based on global consumption rates.
- An out-of-service tank has a direct impact on the supply chain balance, therefore an increase in the total number of ASTs is required to maintain the supply balance.
Tank Lining Compatibility
Selecting the best protective coating/lining for the anticipated services during the life of the storage tank impacts:
- Inspection cycles
- Maintenance costs
- Downtime capacity
- Environmental liability
There are several critical characteristics you will want to consider for determining coating compatibility for tank exposure service:
- Resistance to cyclic stresses from filling /draining
- Resistance to heating and cooling of tank
- Resistance to tank cleaning/inspection procedures
- A coating that is easily repaired and maintained
- Long-term compatibility with a broad range of chemicals and concentrations at anticipated storage temperatures
In our next blog post, we’ll take a look at one instance where a customer was able to extend the service life of his tanks by implementing a rigorous coatings evaluation process that encompassed his entire intended scope of exposures.
To learn more about ARC coatings for above ground storage tanks contact your local Chesterton office.
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