Storage tanks containing hazardous products require interval based inspections to help ensure their mechanical integrity and their tolerances are up to code – meaning safe for the environment and facility operation.  Stainless steel and carbon steel storage tanks often contain caustic or highly corrosive materials that break down and degrade their containers over time, making the inspection process even more crucial.  

External inspections are less invasive than internal inspections, but still provide a great deal of insight into the tank’s structural integrity due to the use of non-destructive testing techniques, such as ultrasonic testing (UT). When a tank is due for an internal inspection, thorough cleaning of the internal floor, shell and nozzles is a very important step prior to the inspection process. Simply put, if the surface is not cleaned, quality inspection is near impossible because surface flaws will be masked. 

Regular aboveground tank inspections are essential for catching possible storage tank failures that could harm facilities, the environment, and personnel. Full-blown disasters can be avoided if facility and plant leaders work with inspectors to address  red flags found during inspection before  costly problems arise. 

API 653 Inspection

The API 653 standard sets the parameters for both external and internal inspection practices and details tank repairs, acceptance of inspection results (minimum tolerances) and inspection  intervals. . . API 653 was specifically developed to provide fit for service standards for tanks built to API 650but it can be  applied to many steel tanks constructed to both know and  unknown specifications. 

When performing an  API 653 inspection , the inspector will review all previous reports that have been kept on record and  look for potential issues noted in prior reports . Reports for this review should be provided by the owner in a monthly inspection report. Having several of these reports available for review will help form a picture of the aboveground storage tank’s health from the beginning. 

Tanks typically larger than 50 feet tall  and greater than 30 feet in diameter fall under this program maintained and written by the American Petroleum Institute (API 653). How often you should inspect your tanks is determined by several factors listed in this program. We will go over several topics so you can be sure you are up to code.

Internal Inspections

For tanks taken out of service, an off-stream inspection is required every ten years. To inspect the tank’s internal components, the first shell course and tank floor plates must be spotless inside before the inspection. There cannot be any rust, water, or product on them as this would interfere with the visual inspection and magnetic flux leakage (MFL) examination of the floor plates. 

The API 653 standard, which “provides minimum requirements for maintaining the integrity of such tanks after they have been placed in service and addresses inspection, repair, alteration, relocation, and reconstruction,” has a visual checklist that inspectors are recommended to follow when performing the inspection. 

For the VT or internal and external visual inspection, the secondary containment, foundation, shell (internal and external), including out-of-roundness, ancillary equipment, sumps, and internal popping, columns for the roof, the roof (internal and external), nozzles (internal and external), floor plating (internal) must all be inspected. 

An ASNT level II certified UT inspector must perform the UTT or ultrasonic thickness testing inspection. This usually includes the internal floor, shell (internal and external), roof, and nozzles. Trained personnel may perform vacuum box testing of the floor plate, lap welds, and chime weld (floor plate to shell weld). At NDT Tanknicians, all of our API inspectors are dual certified API and ASNT Level II: ASNT-SNT-TC-1A (MT,PT and UT). 

Tank bottom examination is performed to scan the aboveground storage tank bottom to look for corrosion (particularly underneath). A magnetic flux leakage (MFL) examination of floor plates is used to locate bottom-side corrosion where the plates are touching the foundation.  

Survey transits or laser measuring equipment is used to perform a settlement survey by trained personnel. During this part of the inspection, it will be determined if the tank is sitting or tilting incorrectly on the foundation. To ensure the tank is level, each side is measured with a laser.

External Inspection 

Tanks that are still in service will have an external inspection, which should be performed every five years to establish if the tank is suitable for continued operation. During this type of inspection by a certified API 653 inspector, secondary containment, external nozzles, external shell, and the external roof will be inspected. For the ultrasonic thickness testing (UTT) inspection, the external nozzle, external roof, and external shell will be inspected. 

All recommendations and results will be compiled in a completed report. Long-term and short-term corrosion rates should be reported, and a calculation on the remaining life of the tank. To make sure the tank is suitable for continued use, the client-approved engineer should review the report. 

Depending on the results of the initial inspections, additional inspections and testing may be needed, for example, magnetic particle testing (MT) or Penetrant Testing (PT) could be used on the welds if indications are suspected to be revealed. These tests are performed to find open-to-surface cracks in welds that can’t be readily seen and are performed at nozzle penetrations or areas of concern discovered during the UTT or VT inspection.

Hire a Certified STI & API Tank Inspection Professional

We are only as good as the service we provide, and we go the extra mile to ensure all of our personnel are trained to industry standards. At NDT Tanknicians, we embrace the tough challenge set in place to be certified by entities such as the Environmental Protection Agency (EPA,) American Petroleum Institute (API,) Steel Tank Institute (STI,) American Society for Nondestructive Testing (ASNT,) and the National Association of Corrosion Engineers (NACE,) to name a few.  

We’re capable of providing top-to-bottom coverage for all of your Storage Tank requirements; servicing a broad spectrum of clientele, both small and large. Our ability to streamline an entire project gives us an edge over the competition by providing our clients with the peace of mind and convenience of trusting one service provider to become familiar with all of their current and future needs, rather than half a dozen. This keeps costs to a minimum, quality control consistent and communication among crews seamless. Request a quote today.