Risk Assessment & Site Survey
A risk assessment was carried out with the site survey, as well as a dynamic risk assessment on arrival at the site. As the tank was underground it was defined as a confined space. The tank needed to be repaired, so the only way to do this was to carry out the tank lining process from inside the vessel. There is a common misconception that diesel is not dangerous like petrol. To a degree it is not as volatile, however is still dangerous and can explode, as well as being dangerous to health.
Stage 1 of the Diesel Tank Lining Process
The first part of the project would be the removal of the manway lid. This was a very challenging part of the project, trying to remove a lid from a tiny chamber with corroded bolts alongside the lovely British weather. Once removed these were set aside. We were then left with an open hole exposing our access point into the fuel tank. The sludge was removed from the base of the vessel with a vaccum tanker. As the tank had not been opened for 20 years, an air change would be needed inside the tank. Fresh air was pumped into the tank for a 10 minute period. A gas monitor was lowered into the confined space and gave a reading of just 19% oxygen. Although not dangerous, we ideally wanted a reading of 20.9% to be on the safe side. To acheive this we continued pumping fresh air into the confined space for a further 10 minutes. This gave us the readings we needed and allowed us to commence stage 2.
Stage 2 – Cleaning the Diesel Tank
A confined space tank cleaner was lowered into the tank using a tripod and man riding winch with G.Saver. Once he had reached the base of the vessel, he removed the man riding winch and remained attached to the G.Saver. The confined space trained tank cleaner manually pressure washed the vessel and removed all sludge and grease from the tank walls and floor. The vacuum tanker removed the remaining contaminated water/diesel from the tank.
The Specialist Lining Services by Eurotank project manager then entered the confined space to inspect the cleaning works. The tank was also inspected for damage and the cause of the sludging.
In order to repair the tank, a diesel tank GRP lining system would need to be installed by our skilled operatives.
Abrasive Blasting of the Tank Surface
Abrasive blasting is challenging in most instances but adding in a confined space makes it a lot more difficult. The creation of dust, low lighting, and being attached to a safety line make this a job not for the feint hearted. The tank was blasted to SA 2.5. This removes all contamination and provides a key for any coating or lining to adhere to. It physically takes away roughly 35-60 microns of the steel, creating peaks and valleys. Blasting also brings up additional flaws in the steel that may need attention. This particular tank had some water ingress which was stopped by SLS using Epoxy mortar repairs. Once the blasting was complete, the spent abrasive was removed to a skip and the tank thoroughly vacuumed before application of vinyl ester primer by roller and brush.
The tank following abrasive blasting and priming.
