Inspections for GRP & Dual Laminate Tanks
Once a GRP or dual laminate tank has been installed, it is imperative to inspect it. If maintained and checked regularly it could last for decades.
One of the main benefits of avoiding the ‘fit and forget’ approach is that the tank’s life span can be increased through inspection.
See the HSE’s ‘advice to user’ guide PM75 for GRP tanks for independent recommendations on inspection techniques as well as the timing and extent of inspections.
MAIN INSPECTION TYPES
ULTRASONIC INSPECTIONS
Tank Inspection Ltd is the UK licensee of the UltraAnalytix™ system of GRP tank inspections. The UltraAnalytix™ system is based on more than 60 years of scientific research, including work originally conducted by NASA.
GRP Tanks can usually be inspected using UltraAnalytix™ while in operation, and without entry into the equipment. These inspections can provide the following:
- Corrosion Barrier condition at and beneath the surface
- Structural GRP condition for mechanical integrity.
- Actual strength and thickness of the GRP to determine its structural capacity.
- The rate of change of its structural capacity.
- Estimated remaining service life.
This is an in-service inspection that is always carried out in conjunction with an expert visual inspection.
Extend, Repair or Replace?
Once you reach the end of a tank’s design life how do you decide whether it is still safe to use?
In the case of tanks already past their design life, our inspector will be able to advise one of the following courses of action:
- Extend operating life of the tank – and suggest follow up test within specified timescale
- Extend operating life of tank – subject to repairs / remedial action
- Condemn the tank and recommend replacement
EXPERT VISUAL INSPECTIONS
The wealth of experience and knowledge our inspectors have allow them to offer a detailed report on the condition of your tanks. This is an in-service inspection that does not require tank drain-down.
High Voltage Spark Testing
Most ‘Dual Laminate’ tanks (GRP with an inner thermoplastic shell) have a carbon fibre conductive strips behind all welded joints which facilitate high voltage spark testing to check the weld integrity at any time during the lifetime of the tank.
Spark testing can only be carried out when the tank is out-of-service and has been drained down and made safe.
When maintained and inspected regularly a tank can last for decades, even beyond its design life.
SAY 'Goodbye' to Destructive Testing
If choosing to use a tank beyond its design life, you have to be prepared to justify this decision to the HSE.
Once, the only reliable tank testing method was destructive testing. A hole had to be cut in the side of the tank, and a sample of GRP/Plastic was sent away to have its residual strength assessed. This was the only reliable way of extending the design life of a tank.
Now with UltraAnalytix™ there is an alternative method. Ultrasonic tests are carried out at the points of worst loading, for instance at the bottom of the tank and at the branches / connections under the most stress.
The data collected is analysed against existing data sets to provide a comprehensive trend of the tank’s residual strength.
