Do your tanks meet the applicable Standards? Are your tanks safe?

Three major events in the late 1980s involving failures and leakage of aboveground storage tanks (AST) prompted stricter regulations on the national, state, and local level. AST owners must now comply with these new regulations. Thielsch Engineering has designed an AST inspection program to provide tank owners and operators with a response to satisfy these requirements.

The program addresses, although is not limited to, the following:

• Corrosion remaining allowance
• Maximum allowable liquid height
• Projected tank life
• Presence of stress raising defects or design defects
• Extent of corrosion and/or pitting damage
• Fracture toughness properties at low ambient temperatures.

Thorough visual and meaningful nondestructive examinations performed by trained, highly experienced and qualified personnel provide critical information to determine the current condition of the tank. Structural members, shell courses, floor sections, valves, drains, piping, floating and fixed roofs, foundations, etc., are examined to determine the extent to which further inspection is required.

Various modes of AST settlement can occur during the service life. Differential settlement and edge settlement are responsible for a majority of structural problems. Computer-aided analysis is performed to evaluate the extent of settlement relative to the specific requirements of API Standard 653.

Bottom corrosion is also of concern. The extent and rate of corrosion determine the inspection frequency. Several methods can be utilized to examine the tank bottom. Attention to this area will minimize the likelihood of leakage.

All welded components/structures contain flaws or imperfections to some degree. These flaws can range from slag inclusions, porosity, lack of fusion, and/or lack of penetration to cracking/fissuring. Further, base materials can contain flaws such as surface laps, slivers, laminations, hot tears, etc. Service-related cracking can also develop in conjunction with or independent of these conditions, depending on stresses and service environment. These flaws may result in defects that affect the overall tank integrity. In many instances, however, these flaws in no way affect tank integrity. It is therefore essential to understand the significance of locating and evaluating flaws. Some steel plate materials are, or have become inherently very brittle during manufacturing, erection, and welding or service. Thielsch Engineering has a long history of evaluating these types of structures to a variety of industries including power, pulp and paper, chemical and petrochemical, pharmaceutical, cement, etc.

Our API certified inspectors use visual, magnetic particle, liquid penetrant, ultrasonic, radiographic, and magnetic flux examinations as well as vacuum box testing to locate and evaluate defects and discontinuities. Elevation surveys are performed to identify differential, uniform, and planar settlement. Additional evaluations can also be performed in the laboratory to determine material composition and properties (i.e., chemical/metallurgical analysis, Charpy V-notch, and tensile testing, etc.), if necessary.

A detailed engineering report is prepared including all data and analyses as well as recommendations to ensure safe continued service, and to serve as documentation for future inspections. All reports are reviewed and sealed by a registered Professional Engineer.

For additional information on Above Ground Storage Tank Inspection contact Peter Kennefick at pkennefick@thielsch.com.

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