Storage tanks are fundamental elements of any industry. Given how crucial storage tanks are, it’s imperative to ensure they are in proper condition. Storage tanks are susceptible to contamination, leakage, and corrosion that may result in product loss and present a situation for environmental degradation. However, storage tank maintenance and upkeep must only be performed by professionals equipped with knowledge and experience to conduct such tasks.

Businesses and industries that rely on storage tanks and containers are advised to invest in API 653 tank inspection services.

API 653 standard was laid down with the aim to provide a guide to the inspectors for repairing, installing, altering, dismantling, and inspecting storage tanks that are designed according to API 650 or API 12C codes.

It’s important to note that the API 653 standard is limited to the foundation, bottom, structure, roof, nozzles, and tank shell. Unlike STI SP001 inspection which is done to on small field-erected tanks, API 653 tank tests are more conservative in nature.

When inspecting an in-service tank’s degradation, other norms and codes like API 579-1 or ASME FES-1 (Fitness of Service) are applied. These norms and standards are considered during the acceptance procedure. For a proper and adequate evaluation of tanks, one must be familiar with these regulations.

In case the tanks require physical modification, there is a need for an assessment of the tank’s future integrity.

When tank integrity evaluation is conducted, various factors must be kept in mind. The main factors to consider are the environmental condition, the product store, loads, the foundation of the tank, and the tank’s alteration.

API 653 standard also specifies inspection requirements in detail. When conducting regular or annual inspections of “in-service” tanks, the inspectors must follow the procedures given in Section 6 of API 653 Standard.

In-service tank inspection and its purpose

In-service tank inspection is carried out to ensure the tank’s structural integrity stays intact when in use. To check the integrity of the tank, an external assessment is required. Visual inspection, tank’s thickness analysis, and Cathodic Protection (CP) test are some of the most common external tank testing methods that are put to use.

Another crucial aspect of in-service tank testing is the frequency of the inspection. How frequently tests should be conducted depends upon the corrosion rate, history of the tank, and type of tank inspection.

According to the API 653 inspections standard, the frequency of tank inspection depends upon various factors. Some of them are:

  • The products stored in the tank and its nature
  • The outcome of visual inspection
  • The range of corrosion in the tank
  • Corrosion tolerance of the tank
  • The readings of the previous inspection
  • Corrosive prevention system in place
  • Tank location
  • Air and water contamination risks
  • Tank operating mode and changes to it
  • Federal, State, or local law that governs the area
  • Change in service

Since tank testing is a highly specialized field, it should be done by someone who has taken API 653 training course.

A large chunk of API 653 Standard is dedicated to tank repair and alterations. According to the norms, all the tanks’ modifications can only be sanctioned by an authorized API 653 tank inspector.