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.

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UPDATE ON COVID-19: KIEFNER IS OPEN FOR BUSINESS AND CONTINUES TO BE AVAILABLE TO SUPPORT ALL OF YOUR ENGINEERING NEEDS

Amid the ongoing concerns related to COVID-19, Kiefner and Associates, Inc. (Kiefner), and its parent company Applus+, is closely monitoring and responding to the situation. As a dynamic partner, we have rapidly adapted our operating approach in order to best serve our clients’ needs.  This includes the formation of our Crisis Management Team that has taken charge of safeguarding our employees and minimizing disruptions to operations.

As this is a developing situation, our approach is continuously evolving. Our protocols are being adjusted as needed in line with the progression of COVID-19 meet or exceed the latest Center of Disease Control (CDC) guidance. Our top priority has always been, and continues to be, the health and safety of our people, our clients, and our business partners.

As a Critical and Essential Infrastructure services provider, we recognize the important and special responsibility we hold to maintain normal work schedules and operations to keep our nation functioning. While much of our work may be performed remotely, we would like to inform that our laboratory remains fully functional and we are available to receive test pieces at any time. We remain committed to supporting our customers. Contact your Kiefner representative to discuss further today.

Be assured that Kiefner and Applus+ is taking appropriate action to maintain ongoing operations, including:

  • Active implementation of Center for Disease Control and Prevention (CDC) protocols.
  • Providing 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 and remain in full effect.
  • Kiefner 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.

Kiefner remains open for business and is committed to delivering all services in response to our clients’ needs. We will continue to protect our employees, customers and business partners, while delivering quality and maintaining high standards of customer service.

As always, you should feel free to contact us with any questions. You can reach me by email at gary.stein@kiefner.com.

Thank you for your support and partnership,

Gary Stein
Gary E Stein, Esq.
Strategic Business Partner Manager
Kiefner and Associates, Inc.
T 614-410-1611
E gary.stein@kiefner.com