28/04/2020

What are some of the Widely Used Tank Inspection Methods for Petroleum?

Any regulated petroleum tanks must undergo leak detection or release detection processes to identify any early signs of contamination from an underground storage tank site.

The responsibility of an API tank inspection professional includes detection of leak in petroleum tanks, ensuring the leak detection process is per the testing instruction set by the manufacturer, and the leak detection system is properly installed into the system.

According to Section 280.43 of federal regulation, there are seven methods to conduct release detection for petroleum; four of them are described below.

Before jumping into the details, it’s worth mentioning that if anyone method of leak detection is solely relied on, there can be a chance of missing out on any potential issues. Thus, there should be a proper system with integrated methods in place to ensure no faults get undetected.

Method 1: Automatic Tank Gauging System

In an automatic tank gauge system, the leaks are detected by measuring the inventory together with tracking of activities like delivery and dispensing of the oil.

In this method, the API inspection companies use probes to detect leak of each tank, ATG, and a leak testing software. 

According to the standard regulation, the automatic tank gauging system should be capable of detecting a leak of 0.2 gallons/hr. It should have a 95% detection probability with a 5% rate of false alarm. Besides this, the ATG should be able to perform inventory control. 

Method 2: Vapor Monitoring

In the vapor monitoring method, the inspector measures fumes produce in the soil due to the leaked petroleum product. 

The equipment required for the VM is, vapor sensor to monitor wells, an automatic tank gauge to monitor the vapor sensor. 

To conduct the vapor monitoring, the tank inspectors must ensure that there are porous materials in the testing zone. The excavation area should have no interference from groundwater or rainwater. Besides this, there must be adequate numbers of monitoring wells in the area.

Since there is a delay in leak detection and chances of wet sensors is high, the vapor monitoring is not considered as a stand-alone leak detection method.

Method 3: Groundwater Monitoring

In groundwater monitoring, permanent monitoring wells are placed near the underground storage tank. These wells are monitored and checked ones in a month to look for released products that may have collected in the wells. 

For proper groundwater monitoring, equipment like groundwater sensor and ATG is used.

When conducting the leak detection, it should be made sure that the level of groundwater is 20 inches of the surface. The system must be capable of detecting 1/8 inches of the product above the groundwater level.

Just like vapor monitoring, groundwater monitoring is not considered fit as a sole inspection method since there are chances of delayed detection.

Method 4: Interstitial Monitoring

In interstitial monitoring, secondary containment is used for leak detection. Double containment like double-wall piping or double-wall tank works as an added barrier between the piping system and the environment. The secondary containment captures the leak between the walls. This leak detection method is permissible for all tanks that are installed after 2016.

For interstitial monitoring, equipment like doubled walled UST, brine-filled, dry space, bladders, and impermeable excavation liners is used.