Investigation of Interior Corrosion of Above-Ground Storage Tanks

Barry Hindin, PhD, PE
Senior Principal Engineer
Kiefner and Associates, Inc.


The Failure Analysis and Welding (FAW) group at Kiefner traditionally investigates the causes of failures of buried pipelines carrying various petroleum products ranging from crude oil, refined liquid products, natural gas and its condensates. However, many of our customers do not know that Kiefner also has the expertise to investigate failures not only of other types of oil and gas equipment such as valves, fittings, pumps, and tubing but also equipment completely unrelated to the oil and gas industry. Recent examples include conducting failure analyses of aluminum sheet used in heat exchangers, metal coatings used in garbage disposers, and stainless steel containers used in food refrigeration systems. This blog, that is expected to be part of a series of blogs, will focus on a recent investigation of premature corrosion occurring inside an above-ground storage tank.


A newly built carbon steel tank with a floating roof was hydro tested prior to being put in service to hold liquid petroleum products. An example of such a tank is shown in Figure 1.

Figure 1. Example of an Above Ground Petroleum Product Storage Tank

The tank was filled with over 4 million gallons of water and while the actual hydro testing of the tank required only a 24-hour hold of the water to check for leaks (none were detected) the entire process of filling and then emptying the tank took 23 days. During this time, uncoated carbon steel was exposed to potable water taken directly from a nearby fire hydrant. After the tank was emptied and allowed to dry of a couple of days, the interior surfaces of the tank were visually examined by entering the tank (Figure 2) and was found to be coated with an unexpectedly high concentration of rust deposits.

Figure 2. View of Interior of Storage Tank after Hydrotesting (Floating Ceiling Lowered)

A closer examination revealed that the corrosion was a localized attack that resembled small mounds of rust. These deposits are also known as tubercles because the interior of the mound is usually porous or even hollow (Figure 3).

Figure 3. View of Rust Tubercles on Ceiling of Storage Tank after Hydrotesting


The bottom of the tubercle acts as the anode while the uncorroded metal surface outside the mounds serves as the cathode in an electrochemical cell. These tubercles are also often associated with microbiologically-induced corrosion (MIC). MIC is often seen on the exterior surfaces of buried pipelines because of the bacteria-rich environment in surrounding soils. However, MIC can also be present in locations not normally associated with bacteria. A sensitive technique for identifying the DNA of bacteria present in a sample called quantitative polymerase chain reaction (qPCR) was used to identify several types of bacteria and the amount present in the collected corrosion products and was also used to determine which percentage of the bacteria were alive and dead. Subsequent analysis of the collected corrosion products from the same tank after two months of continuing to dry out the interior revealed that almost all the bacteria had died. An analysis of the testing procedure revealed that the practice of aerating the incoming water to remove chlorine from the water had a deleterious effect on causing the observed rust and promoting MIC growth.

Comments are closed.


Applus+ is a specialist service provider of non-destructive examination and inspection services which are critical to ensuring the safety and integrity of the energy and industrial sector. Accordingly, please be informed that Applus+ and its affiliate companies, including but not limited to Applus RTD USA, Inc., Applus Velosi America, LLC, Applus K2 America, LLC, and Kiefner and Associates, Inc. are open for business.

Applus+ is deemed as an Essential and Critical Infrastructure service provider. The services provided by Applus+ ensure our client’s continuous safe operations, delivery of essential services to our end clients in these times of need, and supports compliance with local, state, and federal regulations—include our united mandate to continue providing Essential and Critical Infrastructure services.

Operating for over 85 years, Applus+ has responded to emergency situations in high consequence areas and at times when other suppliers have been unable to perform. We believe that we have not only demonstrated value but sincere commitment to quality and service. Applus+ will continue to show its unwavering support at the request of our clients to assist in maintaining operational continuity.

We would like to let you know what measures Applus+ is taking to ensure the health and safety of our employees, clients and suppliers.  We have activated our Business Continuity Plan and the purpose of this Plan is to ensure uninterrupted service. As the situation develops, our management and protocols will be adjusted, as required.

Applus+ has taken the following measures:

  • Active implementation of Center for Disease Control and Prevention (CDC) protocols.
  • Provided information to employees about the Coronavirus, its symptoms, and how to minimize its spread. Employees have been advised to avoid crowded areas and to limit social interaction, and have been trained on the correct hygiene, health and safety procedures.
  • Internal protocols have been implemented to follow all CDC guidelines for all who:
    • Have travelled internationally within the last 14 days
    • Have been in close contact with someone who has been confirmed infected with or is being tested for COVID-19
    • Have been in close contact with someone who is under self-quarantine.
    • Have any symptoms such as fever, coughing, and shortness of breath.
  • Effective 03/17/2020 short-term remote work guidelines for employees have been implemented.
  • Applus+ has increased the frequency of cleaning services in our facilities to ensure a clean and safe working environment.
  • Travel has been limited to essential client-required travel only, with severe restrictions in the case of high-risk destinations.

We will continue to monitor the situation in order to adapt in a timely and effective manner as the situation evolves. Our goal is to ensure that we fulfil our commitment to our clients and deliver the highest standards of service excellence, while at the same time keeping our workforce safe and healthy.

As always, you should feel free to contact us with any questions. Please email the team at for further assistance regarding the COVID-19 matter. To schedule services, continue to communicate with your Applus+ representative.

Thank you for your support and partnership,

Applus+ Management Team