Cold-bonding polymeric techniques prove their advantages over welding

Louise Smyth

Examining the cold-bonding repair of a heavily corroded diesel tank, Tom Belli discusses how a train refurbishment company are able to restore dilapidated trains to like-new condition in minimal time, while ensuring long-lasting protection

Over the course of two centuries, railway networks throughout the UK have changed significantly from the original public railway, to become what many of us use today. 

However, the vast majority of trains still charting their journey around the country have been in operation since the late 1960s or early 1970s. Therefore, with such an extensive service life, these trains continuously require repair and maintenance in order to keep them running. In fact, some have been left to rack and ruin after having been stored in sidings for up to 30 or 40 years, during which time the effects of vegetation and corrosion have taken their toll.

At the beginning of 2015, Belzona was contacted by a UK-based company specialising in the restoration of dilapidated trains. Once salvaged, train refurbishment involves dismantling in order to conduct varying degrees of repair and maintenance, before repainting and returning to a like-new condition. Not only does this provide a cheaper alternative to purchasing a new train, but it also delivers a new lease of life to many of these abandoned diesel-electric freight trains.

During the refurbishment process, the company identified a recurring problem with the diesel tanks. Originally, the undersides of all diesel tanks were covered with fibreglass as a protective barrier against sparks flying up from the tracks. 

Critically, moisture would enter the gaps between the fibreglass and the steel tank, causing corrosion of the metal; in some instances this appeared as pitting or even holes. Their present repair method comprised of grit blasting the fibreglass away from the diesel tanks and welding steel plates over the weakened areas.

However, subsequent pressure testing revealed that welding was causing further cracks or weaknesses in the steel around the various HAZ (heat-affected zones). These weaknesses were compounded further by additional weld repairs and pressure tests before the company was satisfied with the final outcome. This proved to be both time consuming and expensive.

The customer required a cold-applied solution to repair these defects, ensuring that further damage from hot work did not compromise and slow the repair process.

After consultation, Belzona 1121 (Super XL-Metal) was selected as an appropriate material to restore the diesel tanks to working condition. Initially, the surface was prepared in line with Belzona protocol, before metal plates were cold-bonded onto the damaged steel. With application and curing at room temperature, Belzona 1121 offered a corrosion resistant solution which was able to eliminate the threat of HAZ and significantly pass the pressure tests first time. Finally, the repair was coated with GRP (Glass-fibre Reinforced Plastics) and painted black, in line with the remainder of the tank.

Significantly, the customer was satisfied with the speed of the process in comparison to their traditional repair method. This allowed the repaired tanks to be refitted onto the trains far quicker, whilst also offering a long-term solution for their initial problem. Belzona 1121 has since been incorporated into their authorised specification for all diesel tank repairs and is now a company approved repair method.

Polymeric cold bonding techniques such as these have been used throughout industry, completing applications in environments from mining to oil and gas. Regardless of the type of machinery and equipment or buildings and structures, Belzona’s polymeric materials have provided countless solutions, with proven results.

Tom Belli is with Belzona

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