Exempting Atmospheric Storage Tanks from Hydrostatic Testing

By: Devon Brendecke, Consulting Engineer, Quest Integrity GroupAs seen in the March 2013 issue of BIC Magazine - view the article as it was published.

Thanks to the widely growing acceptance of fitness-for-service methods, large atmospheric storage tanks can now be exempt from hydrostatic testing following repair. API 653 allows the use of a thorough fitness-for-service assessment in lieu of hydrostatic testing. The exemption has been included in the past several editions of API 653 and is becoming more widely used. In many cases, the benefits of the hydrostatic test exemption greatly exceed the cost savings. Although the data requirements for this type of assessment are extensive, the exemption eliminates the time and logistics required to conduct a hydrostatic test. Engineers with specialized consulting experience and software make hydrostatic test exemption a viable option.

While the benefits of the exemption go beyond fiscal savings, it is often one of the motivating factors in decision making. For large tanks, the downtime required for filling and emptying the tank is prohibitive. A large diameter tank can take weeks to fill, hold and empty, whereas the analysis for the exemption can take as little as a week. For many regions in North America, acquiring the amount of water needed to conduct the test is nearly impossible. In other regions, disposing of the water after testing is exorbitantly expensive and can increase the emptying time based on disposal logistics alone. Cold weather conditions can also make hydrostatic testing difficult. The hydrostatic test exemption avoids all of these potential complications and costs and has been successfully performed for more than 10 years.

The exemption analysis requires little beyond that which API 653 requires following a repair. Thorough inspection of all new welds is already a requirement; however, evaluation of the weld procedures by a qualified engineer is also necessary. To ensure all potentially problematic issues have been addressed, the most recent API 653 out-of-service inspection report must be reviewed by the engineer conducting the analysis.

It is also necessary to ensure proper materials and repair design and procedures were used. The last critical piece of information required by the fitness-for-service standard is fracture toughness of the newly welded regions. The fracture toughness is measured with a destructive test and can be performed on a sample of material removed from the tank during the repair. The material testing can often be completed in parallel with the majority of the analysis, which contributes to the quick turnaround for the exemption.

Quest Integrity Group provides hydrostatic test exemptions as part of its advanced engineering services. The company’s background in fitness-for-service makes it uniquely qualified to deliver advanced engineering assessment solutions to terminal and production clients. Its team of dedicated engineers has successfully completed hundreds of analyses, establishing it as a leading tank assessment company.

For more information, visit our storage tank integrity assessment page.