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Products and solutions, 2007-05-16, 11:02 AM

Protection for power plant components

A very special service involves protecting condensers in power plants from corrosion. Exclusively produced for ThyssenKrupp Xervon, Plastocor is the 2-component epoxy resin that a special team of the Company has been using for decades to protect tube bottoms, water chambers and tube inlets and outlets from premature aging with atmost success. In a new form of application, the cold-reactive material is now even conquering the hitherto unprotected tube interior. In the so-called tubelining process, the inner surfaces of the tube can be coated over their entire length without appreciably reducing the condenser’s heat transmission.

There is scarcely a power plant anywhere in the world without the patented Plastocor coating system. Its field of application is the cooling water circuit, where Plastocor protects mainly condensers, but also heat exchangers, oil coolers, pump casings and cooling water pipelines for many years from corrosion and erosion. Thanks to the special formulation, the extremely robust coating is resistant, for instance, to cooling water, seawater, various chemical components, and solids-laden emulsions and liquids at temperatures of up to +80°C. Plastocor System 2000, which was specially developed for use on tube bottoms, comes with a five-year warranty. In practice however, the service life of the coating, which is always applied by hand, is many times longer – partly because damaged areas can be repaired without difficulty even after many years of service. The coating doesn’t change chemically over the years and the old and new coatings always form a firm bond.

For old and new

Plastocor is just as suitable for the protection of new condensers as for the rehabilitation of old con-densers. Such rehabilitation recently took place in Denmark’s biggest coal-fired power plant, which is operated by energy supplier Dong-Elsam in Aabenraa. A special ten-strong team rehabilitated a main and a spring pump condenser with Plastocor within the space of five weeks. The contract comprised the coating of the steel water chambers, tube bottoms and tube inlets and outlets. The rehabilitation had become necessary for several reasons. Firstly, the existing water chamber coating was old and brittle. Furthermore, the tube bottoms and inner tubes – both made of a special brass – didn’t have any protective coating, and erosion damage had occurred in the rolled joints.

Only five years earlier, a Plastocor team from ThyssenKrupp Xervon had coated a water chamber at Aabenraa power plant. Encouraged by the positive experience with this coating, the operator then decided to carry out the recent Plastocor rehabilitation, which was handled in connection with a major inspection. The roughly 300 square meters water chamber surfaces were given corrosion protection with Plastocor 400 K in a total thickness of 500 µm. This system consisting of three dif-ferent-colored films is specially intended for water chambers flooded by cooling water and is applied almost entirely by hand.

Using Plastocor 2000 to combat erosion

Plastocor 2000, a coating always applied with a trowel, was developed for application on tube bot-toms. The system only works together with conical system plugs specially made for this purpose that serve as a negative mold. Before application, they are inserted as far into the tube as required for the desired coating thickness. Then the coating system is applied in several layers. After inter-mediate drying of eight to twelve hours at +20°C, the troweled surface is then sanded, the plugs are removed and the tube end-sealed. In its final, hardened state, the coating replicates the conical shape of the system plug, thus ensures turbulence-free inflow into the cooling water admission tubes and protects the rolled joints from corrosion.

In Denmark, the tube bottoms were only end-sealed, however, with a maximum film thickness of 800 µm. These were joined by 72,000 tube inlets and outlets, which were protected with an 80 to 120 µm thick, triple-layer Plastocor coating (250 or 100 millimeters deep into the tube interior). The coating system not only eliminates existing erosion and corrosion damage, but also provides long-term protection from new damage, particularly at the rolled joints.

Tubelining for a long service life

AA new, machine-applied variety of Plastocor has now been developed that permits the coating of the entire condenser tube in situ for the first time. The decisive advantage of the process known as tubelining is that the applied coating does not reduce the performance of the condenser than any entirely normal changes of an unprotected tube. On the contrary, while the heat conductivity of a new, uncoated tube declines after only a few months of operation due to fouling, erosion and corro-sion, a tube protected with Plastocor maintains heat transmission at a high level for a long time. This is also because, for example, the hydrophobic surface is resistant to certain forms of fouling and is thus easier to clean and maintain. In field tests, Plastocor-coated tubes have already achieved a service life of five to eight years and more. The coating is applied semi-automatically with a purpose-built tubelining machine. Here, a hose equipped with an airless spray nozzle initially runs through the tube to the end. Then the nozzle starts to apply the material, and while the hose is being retracted, the tube interior is coated over its entire length. A computer controls all the critical parameters. Tubelining is performed in situ at the condenser and is suitable for tubes from 18 mil-limeters in diameter and up to 16 meters in length.

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