TANK INSPECTIONS

Since API 653 was introduced, operating companies have adopted a more comprehensive approach to the inspection of their storage tanks. The API 653 document describes the minimum requirement for the maintenance of storage tanks. Traditionally, all of this inspection was performed using manual techniques. However, the availability of new technology to scan large tank surfaces is altering the inspection methodology.

  • Tank Floor Inspection

    • In the past, tank floors were inspected by cutting coupons from the floor to establish a baseline for the soil side condition of the floor. Since the introduction of a magnetic floor scanner, during 1989, the floor integrity no longer needs to be destroyed by removing coupons. IRISNDT uses various magnetic flux exclusion (MFE) floor scanning tools.

    The IRISNDT MFE tools:

    • Have from 12 to 24 active sensors

    • Are battery operated

    • Inspect steel floor up to 0.375" thick

    • Inspect through up to 0.100" thick coatings

    • Do not require umbilical cords

    These innovative MFE tools allow us to screen tank floors at rates as high as one thousand square feet per hour for soil side corrosion. The main preparation required is to clean the floors and free them of loose debris (such as scale). The MFE tool detects corrosion whether it is located on the process or the soil side of the tank floor. The magnetic field cannot differentiate process from soil side losses. The magnetic field detects the material volume loss and so, on occasion, a small diameter deep pit may have the same magnetic signal as a shallow large diameter pit. Since the data from the tool is qualitative, we have to perform additional inspection to quantify the corrosion depth. This is quantified using a mechanical pit gauge for top side corrosion, and ultrasonic inspections to access soil side losses.

    • Ultrasonic Inspection

      • Ultrasonic techniques have been used to perform thickness measurements for more than forty years. In the early years, flaw detectors used bulky non solid state devices whose performance tended to drift as the unit warmed up. Today's devices are solid state and remain stable in a variety of temperatures and environments.

      Probes have also improved from the original quartz based devices. Polarized ceramics provide vastly improved performance characteristics that enable many different materials to be inspected.

      The tank floor is just one component of the tank which requires inspection. In addition the shell, roof, foundation, and appurtenances require visual and ultrasonic inspection. A comprehensive checklist aids the inspectors to examine all critical areas. The report documents the inspections performed and includes a drawing of the tanks' floor, roof and shell which highlights all the areas requiring maintenance.

    • Shell Inspection

      • The tank floor is just one component of the tank which requires inspection. In addition, the shell, roof, foundation, and appurtenances require Visual and Ultrasonic inspection. A comprehensive check list ensures that all aspects of the inspection are completed by the inspector.

      The report documents all the inspections performed and includes a drawing of the tank's shell which highlights all the areas requiring remediation.

For further information, please view the following brocheures: