The vertical storage tanks with flat bottoms must meet the API 650 standard. This standard not only dictates the design of the tanks but also the process for manufacturing it as well as the inspection and installation.

API-650 tanks typically hold products such as water, crude oil, petrol, and other chemicals with low internal pressures. Tanks may be built in the factory or on location. They may come with a domed roof or cone-shaped roof. They may include anchors along with stiffening rings. A typical vertical storage tank will have a staircase or stairway or possibly even a cage ladder.

Once the fabrication of an API-650 tank is completed, it must be inspected. All inspections must be performed by an inspector who is licensed and trained on the requirements. They will review the description of the tank, which includes the specifications, construction of the tank and methods of release. They will also review plans for spill control.

The inspection will include the bottom of the tank and the roof along with the shell. The inspector will conduct a visual inspection as well as an ultrasonic review. Other types of inspection include the following:

• Magnetic particle

• Tracer gas

• Liquid penetrant

• Radiography

• Vacuum box

• Penetrating oil

When the inspector looks at the roof, shell, and bottom of the tank, they consider the minimum remaining thickness as well as the required thickness and maximum corrosion rate. They will look at how the tank is settling into the ground and whether it is tilting. They check for uniformity, settlement along the edge and rigid body tilting.

Along with the initial inspection, monthly inspections are recommended. These inspections may be performed by the owner of the site or the operator. Their job is to assess the overall condition of the tank. No certification is needed for the monthly inspections, but the records should be maintained for the regulators.

A third kind of inspection is also required, which is an external inspection done every five years. It may happen more frequently, depending on what is found in the initial inspection. These inspections must be done by an inspector who is certified. They will review the periodic inspections and test the tank thickness. They will compare the original thickness of the shell with the current thickness. The inspector will also check for uniform settling or determine if settling is occurring more to one side.

An internal inspection is needed once every ten years unless an initial assessment determines it is needed more often. This inspection must also be done by a certified inspector to determine if it may be kept in service. The tank must be taken out of service for this inspection and thoroughly cleaned. Multiple tests may be conducted similar to the initial inspection with findings recorded in the tank’s file.

To avoid fines and other penalties with inspections, it is important to keep a formal inspection schedule and record all findings with each visit. This protects you from future problems if there is an issue with the tank.