Tank Inspection

Any supply distribution system has the important goal of meeting the demands of consumers in a timely and cost-effective manner. The same is true for the petrochemical industry. This sector typically employs aboveground storage tanks (ASTs) for storing petroleum product to balance supply and demand. This highlights the importance of the availability and reliability of these critical assets.

Tank inspection ensures the safety and integrity of tanks by preventing accidental leaks and avoiding costly decontamination, while providing critical data so lifetime and repair predictions can be made. Tank inspectors provide trend info on current asset condition and recommended actions for owners and operators to secure a statutory operating license; they can potentially negotiate lower insurance based on validation that plants are in good condition.

Despite their apparent simplicity, many tank components must be inspected. Tank inspection includes assessing the infrastructure of fixed or floating roofs including domes and seals, shell aperture, settlement analysis and strapping. Both internal and external corrosion usually take the form of isolated attacks governed by roof geometries, construction methods, plate flatness, and coating conditions. Critical areas involve bottom plates, shell plates, annular rings, roof plates and all welding joints. While it’s assumed that leakage will occur before a failure, highlighting thin areas of a tank shell, this is not always the case; there may be catastrophic failure without any prior leakage. Monitoring the tank exterior for general metal loss in various areas provides a useful integrity assessment, but the extent of inspection necessary depends on the product stored, tank age, and historical inspection results.

Tank Floors

A common failure mechanism is leakage through the floor, damaging the tank foundation which leads to instability possibly resulting in catastrophic failure. The most common technology used to inspect bottom plates for corrosion is magnetic flux leakage (MFL) because of its sensitivity to volumetric variations. MFL uses a strong magnet to induce a magnetic field in the bottom plate. When it encounters corrosion of a certain size, the magnetic field “leaks”. The more important the proportional volumetric rate, the greater the leakage. Leakage is detected by a combination of several types of sensors, but MFL technology is incapable of detecting whether defects are on the top or bottom side of plates. For this reason, we combine MFL with surface topology air-gap reluctance sensors (STARS). This enables completely mapping storage tank floors and discrimination between top and bottom defects. The FloormapX is the most advanced magnetic flux leakage floor scanner on the market, complemented by Handscan, an inspection tool ideal for storage tanks 10 meters (33 feet) or less in diameter, petal floor plates, and in-situ heating coils. Floormap vastly reduces the time it takes to inspect tank floors while producing detailed and accurate reports, enabling engineers to determine optimum maintenance strategies.

ACFM is a cost-efficient and reliable method for inspecting storage tank welds, capable of detecting and sizing cracks through coatings without the need for surface preparation. It offers undeniable cost savings compared to MPI by eliminating the labor-intensive process of coating removal and recoating. ACFM inspections are typically six times less expensive than MPI while providing reliable results and comprehensive data records for asset owners. To further enhance the cost and productivity advantages of ACFM, advanced array probes are employed for various weld types, including fillet welds, butt welds, and lap joints. The ACFM fillet weld array probe features a rugged monoblock design and incorporates a clever crack length estimation method, making it ideal for targeted inspection conditions. When assessing floor and shell joints, including lap joints, the high-speed ACFM array probe offers additional cost reductions compared to MPI. The overall inspection process becomes up to five times faster than with previous ACFM probes. The array probe scans areas up to 90 millimeters (3.5 inches) wide, utilizing twin-field technology for biaxial crack detection and sizing.