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Products and solutions, 2006-03-16, 01:01 PM

Blast cleaning, washing, zinc priming and coating

At Marl Chemical Park, the salt works in Europe´s biggest fully integrated PVC production plant underwent rehabilitation at high speed over the last few months. The plant consisting of apparatus frames, tanks, pipelines and pipe bridges, which had been badly attacked by the salt-laden air over a period of years, was cleaned down to the bar steel exterior. After this it was zinc-primed and coated to give it new protection from corrosion. So that this will last for as long as possible, the corrosion protection experts from ThyssenKrupp Xervon offered VESTOLIT GmbH a special procedure for surface preparation to be carried out in cooperation with the client´s full-service maintenance provider. This involved rinsing the plant components with deionized water after the first blast-cleaning cycle. This removes the chlorine ions from the metal and prevents the premature failure of the anti-corrosive system.

PVC has been produced at Marl using sodium chloride (common salt), electricity and ethylene for over 50 years. The salt extracted from a Westphalian salt mine is piped as an aqueous solution to Marl Chemical Park, where it is treated in the salt works and then supplied to the various process stages. However, since salt and steel are not at all compatible, it had become absolutely essential to replace the anti-corrosive system in this part of the plant. This project also serves as a preparatory step for the construction of a new membrane electrolysis system. From mid-August 2005 onward, general fitters, pipe fitters, measurement and control technicians, electricians, corrosion protection specialists and insulators got working on the roughly 20,000 m² salt works installation. It consists of six plant elements - mainly apparatus frames linked together by pipe bridges. The full-service maintenance providers of the operator´s own Infracor GmbH did the replacing, modernizing and connecting. Infracor entrusted all the corrosion protection and insulation work as well as the scaffold erection required for all the trades to multi-trade service provider ThyssenKrupp Xervon.

Good coordination keeps everything on schedule

Regular consultation and good coordination were indispensable for keeping rehabilitation on schedule. By the end of February - after a good six months of rehabilitation work - the entire project had to be completed. "The deadline pressure was enormous, which is why we were working together with Infracor at five or six different points of the installation simultaneously," says Heinz-Georg Beerenbrock. As a so-called multi-trade project manager, he is in charge of the scaffold erection, corrosion protection and insulation work on site. For Infracor he is the sole contact for all these tasks. "By contributing several trades, we save the customer time and a lot of coordination effort," Beerenbrock confidently claims. However, this can only succeed because he has suitably experienced and skilled hands at his disposal. Since he can´t constantly monitor all activities at once, many jobs are handled by his staff without supervision. Beerenbrock: "I am happy when the phone does not ring. Because no news is good news."

Safety first

In addition to their technical skills, the maintenance providers must also have a blind understanding of the Chemical Park´s safety regulations. "Like everywhere else in the chemical and petrochemical industries, occupational safety & health and environmental protection are right at the top of the list of priorities - whatever the deadline pressure," says Beerenbrock, describing the special challenges of the process industry. It is always extremely important for the client that all maintenance providers strictly observe the safety regulations and are familiar with all the procedures customary on site. Infracor and Xervon have been working together closely and efficiently for several years now. Beerenbrock: "Our various departments have longstanding ties with the Chemical Park under framework agreements. The only really new development is the combination of trades as in this project."

Beerenbrock´s personal specialty is corrosion protection, which he supervises in Marl as project manager on top of his general project management tasks. Under his watchful eye, the on average 15-strong team has to treat about 13,000 m² of steel surface. However, all the rehabilitation work was preceded at the start by scaffold erection. The tireless erectors created access to the up to 25 m tall apparatus frames and their countless connection points. Whatever the trade - general fitting, pipe fitting, corrosion protection or insulation - all the craftsmen required ergonomic and above all safe work platforms for their particular jobs. For example, existing insulation had to be removed, and pipes were released, suspended or even removed so that the corrosion protectors could gain access to every inch of surface, however difficult to reach. The scaffold erection team, 25-strong at the start, later shrank to a ten-man crew whose job was to build, convert or dismantle new creative access structures on a day-to-day basis.

Dust-tight enclosure

Only when the components being treated were fully screened off in a dust-tight enclosure did the corrosion protectors get down to work and prepare the steel surfaces for subsequent zinc priming and coating. In the first blast clean with granulated slag abrasive, the corrosion and old coating were removed (preparation standard 2a). This was followed by washing the metal surfaces with deionized water - a procedure specially developed for Marl´s salt works and successfully tested in a pilot project.

Pipe bridge pilot project

Thomas Pahle, Xervon site manager and multi-trade manager: "The year before last we refurbished a pipe bridge in the salt treatment area. In doing so, our measurements established that the steel was still contaminated with chloride even after removal of the old anti-corrosive system." This prompted us in cooperation with Infracor and the paint supplier to develop a three-stage surface pretreatment strategy, consisting of blast cleaning, washing and blast cleaning. After the first blast cleaning cycle, the components were rinsed with deionized water until the chloride ion concentration had detectably dropped below the critical level. Only then was the surface blasted down to the bare metal in the second cleaning cycle (Sa 3) and given a defined surface profile. This not only ensures good adhesion of the subsequently hot-sprayed zinc primer (100 µm), but also ensures its functional effectiveness as the sacrificial anode that electrochemically protects the steel from corrosion by ion exchange (cathodic corrosion protection). Zinc priming was followed by a 100 µm thick basecoat, a 80 µm thick coat of edge protection meticulously applied to all edges, welds, screw heads etc., and finally the topcoat (2-component polyurethane).

The deadline pressure was immense. All the tasks were prepared and executed with extreme care and the odd unforeseen job emerged without warning, yet the rehabilitation project was always well on time. "The scaffold erectors were at times six weeks ahead of schedule," confirms multi-trade project manager Beerenbrock. On his estimation, this was due firstly to the extremely disciplined approach and close coordination of all the workers and secondly to the quick and flexible response to tasks arising at short notice. "As a big company, it is easy for us, if required, to organized skilled staff and the associated quantities of materials at the drop of a hat and bring them to the site."

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