Specialist Lining Services were called out by a client with an issue with their tank. The diesel stored in the tank was sliding, blocking fuel lines filters on trucks and causing potential breakdowns to the lorry fleet. As with any fuel, water is the main cause of sludge. Due to environmental procedures and reducing emissions Bio Diesel was used.
The main issue with Bio Diesel is the creation of microbial bacteria, these bacteria create water as a bi-product. They then block fuel filters more so than standard diesel with the slugging effect. This of course causes a big issue in the bulk storage of Bio Diesel, especially in a Steel Storage tank. As the water will sit at the bottom it will corrode the steel at the base of the tank. The rest of the steel is completely corrosion free as it is only in contact with diesel. If the problem is not sorted the failures – like on this particular tank, can occur and can obviously become an environmental issue should the corrosion break completely through the steel causing a fuel leak. This particular tank was 20 years old and the tank had never been opened since installation.
The photos show the corrosion to the tank and the damage caused by the water at the base of the tank.
A risk assessment was carried out on the site survey as well as a dynamic risk assessment on arrival to site. As the tank was underground, it was a definite confined space. The tank needed to be repaired so the only way to do this was to carry out the works from inside the vessel. People get the misconception diesel is not dangerous like petrol, to a degree it is not as volatile, but it still is dangerous and it still can explode and be dangerous to health.
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 and the lovely British weather! once removed, these were moved aside. We were then left with an open hole exposing the top entry into the tank. The Vacuum Tanker removed the sludge from the base of the tank. AS the tank had not been opened for 20 years, an air change would be needed inside the tank, so fresh air was pumped into the tank for a period of ten minutes. A gas monitor was lowered into the confined space but only reading 19% oxygen – although not dangerous, we wanted 20.9% to be on the safe side – so the air was again pumped into the confined space for a further 10 minutes. Once the air was deemed safe and breathable, our Confined Space Tank Cleaner was lowered into the tank using a tripod and man riding winch and GSAVER. Once he had touched the ground he removed the man riding winch and remained attached to GSAVER. The Confined Space Trained Tank Cleaner then pressure washed the tank and removed all sludge and grease from the tank walls and floor and the vacuum tanker removed the remaining contaminated water/diesel from the tank before exiting the tank via the man riding winch. The Specialist Lining Services Project Manager then entered the confined space and inspected the meaning works, he also inspected the tank for damage and the cause of sludging. In order to repair the tank due to the damage, a Glass Reinforced Plastic Lining System would need to be installed by our skilled operatives.
The entire tank was sanded for any imperfections using sandpaper, any repairs needed were repaired using Chopped Strand Matting and Chemical Resistant Tissue. SLS Operatives then carefully applied the final coat of Vinyl Ester Resin with added wax to aid with the curing. The tank was then post-cured at 50°c. Not only does this cure the resin coat and laminate, it also increases the molecular structure of the plastic creating a stronger plastic with an even higher level of chemical resistance. The lining system was given the Specialist Lining Services 15 Year Warranty against de-lamination & osmosis.
A Vinyl Ester Resin Glass Reinforced Plastic Lining was chosen for it’s excellent resistant properties against Hydrocarbons. This project had a particularly challenging working environment – working in a cylinder, but with Specialist Lining Services we have the knowledge and working experience to overcome these environments and work safely. The particular lay up was performed by two SLS Operatives internally with one Operative as a confined space safety watchman on top of the Manway. The Operatives applied two layers of 450csm matting and a Chemical Resistant Tissue to the entire tank to create a tank within a tank. SLS utilised an indirect fired heater to dry the lay up system before application of a coat of resin using brushes and rollers. The job of the lay up is the creation of the tank using the existing steel tank as mold. The lining system adheres permanently to the existing steel tank, only ever failing with degradation of plastic which starts after a period of 30 years. Offering GRP as the most cost effective lining material on the market.
Abrasive blasting is challenging in most instances but when in a confined space it is a lot more difficult, the creation of dust, low lighting and being attached to a safety line make this job not for the fainted hearted. The tank was blasting to SA 2.5 – this removes all contamination and provided a key for any coating to lining to adhere to. It physically takes away roughly 35-60 microns of the steel, creating peeks 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 Expoxy 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.