Non-Invasive monitoring of floor condition of above ground bulk liquid storage tanks

Mudge, Peter; TWI Ltd; United Kingdom

Mudge, P.J.; TWI Ltd; United Kingdom
Yang, K.; TWI Ltd; United Kingdom
Neal, B.; TWI Ltd; United Kingdom
Jackson, P.; Eddyfi; United Kingdom

ID: ECNDT-0529-2018
Download: PDF
Session: Oil & Gas 4
Room: H2
Date: 2018-06-12
Time: 10:50 - 11:10

Leakage of fluids from above ground storage tanks is a major issue. There are stringent regulatory requirements for the avoidance of leaks of potential pollutants from tanks, so that there is considerable pressure on tank and terminal operators to ensure that leaks do not occur. The main site for leakage is the tank floor, which may degrade in service owing to corrosion or, in some cases, cracking at welds. Procedures have been developed for the inspection and repair of tank floors, for example those in API standard 653, but the operations required to empty, clean and make safe tanks for regular internal examinations are costly and time consuming. Further, the examinations are usually scheduled on an equal time basis and do not take account of the varying rates of degradation occurring in different tanks. Tanks which require the highest priority action may therefore not be examined or rectified before leaks have occurred.

This paper describes monitoring technology which has been under development for a number of years involving the use of low frequency ultrasound to examine the whole of the tank floor from a number of permanently attached sensors around the perimeter on the outside. The long distance propagation characteristics of the ultrasonic waves used allow signals from one side of the tank to be picked up by a sensor on the other side. By using combinations of transmit and receive amongst the set of sensors, it is possible to cover the whole floor area. By taking readings from the sensors regularly, long term trends in the condition of the floor can be determined. The technique also allows short term variations, for example from temperature fluctuations or changes in the fill levels in the tank, to be separated from changes in the physical condition of the floor.