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Products and solutions, 2006-03-16, 01:02 PM

Explosion-proof: Spark-free cutting with water

2006 In itself, there's nothing special about laying glass-reinforced plastic (GRP) pipelines. However, the process becomes interesting from the technical point of view if the new plastic pipe has to be connected to existing steel pipework under absolutely explosion-proof conditions while refinery operations continue. To make this possible, the maintenance team of ThyssenKrupp Xervon applies a special water jet cutting process.

Responsible for everything from pipework to boilers, ThyssenKrupp Xervon has been - since 2001 - the sole maintenance provider for the Emsland oil refinery in Lingen, which joined the BP Group in February 2002. The tasks of the roughly 50-strong core team include not only the inspection and repair of all heat exchangers, vessels and tanks, but also the maintenance of all existing pipes and the installation of new ones. This also covers the laying of GRP pipes, for which the company is certified. In refinery environments in which explosion-proof conditions are essential, the corrosion-free, lightweight alternative pipe made of plastic can be laid hazard-free without welding and, depending on the medium flowing through it, often has a longer service life than the classical steel pipe or the expensive stainless steel variant with its complicated installation method.

Plastic beats steel

A recently replaced, 60 m long hydrocarbon line made of GRP is expected above all to have a longer service life. The line (nominal diameter DN 200, nominal pressure PN 16) carries the exhaust gases of gasoline and oil products to a collection point where they are then processed further. Although the predecessor steel pipe was only five years old, it already showed corrosion damage. Because the pipe system doesn't form a closed circuit, the exhaust gas mixture accumulates oxygen, and rust and pitting develop relatively swiftly in a steel pipe. For this reason, it was decided to replace the corroding steel line with a GRP pipeline and integrate it into the existing pipework.

Razor-sharp spark-free cut

Although, as Rudolf Schreyer of the Xervon Lingen site explains, the laying of GRP pipes on a refinery site is a run-of-the-mill job for his specially trained staff, this was the first time they'd worked under such special conditions. What Schreyer means in particular is the cutting of the old steel pipes without any sparking whatsoever, as demanded by the operator. They therefore resorted to water jet cutting, which is always adopted when highly explosive pipelines have to be cut. With a maximum pressure of 1200 bar and a flow rate of 7.5 l/min with 10 percent added abrasive, a cutting jet is generated with a maximum width of 0.6 mm. The result is an absolutely razor-sharp cut without any sparking at all.

Another special difficulty with the new GRP hydrocarbon pipe is its routing, which demanded several bends during laying. The laws of physics state that the gentler a bend is, the faster the exhaust gases can be discharged. For a pipe with a diameter of 200 mm, the safety regulations demand a bend radius of 1000 mm. And this bend the Xervon maintenance experts laminated themselves. After all, the employees are certified for the processing of GRP and have a command of the various joining techniques required according to material composition. These can be bonding, lamination, flanging, push-fit socketing and mechanical connection methods.

GRP waste water line

In the meantime, a 660 m long GRP waste water line has also been laid on the refinery site by the Xervon maintenance experts. The pipeline's material with a nominal diameter of DN 100 (nominal pressure 16) is precisely adapted to the conditions of its use. It has to be resistant to the waste water flowing through it, which covers the entire spectrum from alkaline to acid (pH 2 to 12). Rigid foam insulation and a 0.8 mm thick jacket of aluminum sheet also protect the electrically heatable pipe from frost.

"Although GRP pipelines call for shorter distances between supports and thus for a larger number of rests, we can still lay them very quickly," concludes maintenance expert Schreyer. This is due partly to the ease of handling the lightweight pipes and also, and particularly, to the trouble-free joining of the individual pipe sections, which does entirely without welding. "This naturally makes a big difference in refineries, where safety has top priority," explains Schreyer who, from his daily work, is familiar with the enormously elaborate task of encapsulating craftsmen's workplaces.

Because of the positive experience with GRP pipes, the Emsland refinery intends to adopt this pipe-laying procedure as standard in its construction and materials specifications. Further orders are due to follow. There are already plans to lay the entire fire-extinguishing system in plastic. Schreyer: "This means a 100 percent guarantee of rust-freedom and eliminates the risk of nozzles becoming blocked by rust deposits."

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