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imageProtection of Water Treatment Equipment 
imageProtection and Repair of Heat - Exchange  Equipment
imageProtection of Equipment in Aggressive Mediums
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PROTECTION AND REPAIR OF HEAT- EXCHANGE

FIRE

Heat up. Effective protection guaranteed.

Hydropower, thermal, cogeneration and nuclear power plants are our home hearth.

Fire is an ancient symbol of warmth and hearthside. In this age of scientific and technological advancement, a warm hearthside is usually the result of smooth operation of hydropower, thermal and nuclear power plants on which we depend nowadays for heat and electricity. Thermal and electrical energy generation is impossible without heat-exchange equipment. This is why any fault or breakdown of heat exchangers is fraught with a total paralysis of a well run population life support, with industrial accidents and consequently, ten digit amounts in damages.

 Beware of Fire

The basis of any heat exchanger design is a heat exchange surface, which can total several thousand square meters whilst being a mere 0.5-0.6 mm thick in modern heat exchangers. Such a large and thin membrane can be all too easily damaged; this is why one should look after its operational capability immediately upon the launch of the heat exchanger.

 

 Itll Pay off Handsomely

Providing for heat exchange equipment corrosion prevention is cost effective because:

  • The service life of heat exchangers and condensers protected from corrosion and scale with the VICOR-TT coatings is 1.5-2.5 times longer
  • Emergency shutdowns and startups are prevented
  • Fuel is saved
  • More electricity is produced

 We recommend that the anticorrosion protection and renewal of heat exchangers be carried out in the following three stages:

  • Protection and encapsulation of the junctions of heat exchange tubes with the tube plate, these being the areas most prone to corrosion
  • Protection and encapsulation of the inlet and outlet sections (150-500 mm deep) of heat exchange tubes
  • Protection by way of filling through holes all over the heat exchange tube

The use of optimal technologies and custom-developed anticorrosive compositions make it possible to repair faulty units quickly and with requisite quality.

If necessary, condenser encapsulation and anticorrosive protection can be carried out duct by duct and sector by sector, without shutting down the generating unit.

 The VICOR-TT System is Your Logical Choice

METACOR-01-UNO, METACOR-02-TSVET, METACOR-05-SIAL,  METACOR-07 TT primers, VICOR-8010-TT, VICOR-8093-TT, VICOR-8095-TT coatings

 

 TUBE  SHEETS, INLET AND OUTLET SECTIONS OF HEAT EXCHANGE TUBES

 Numerous inspections have made it possible to identify the following three principal kinds of corrosion damage in heat exchangers:

  • Corrosion at the junction of a heat exchange tube with the tube sheet
  • Erosion-corrosion of the interior of inlet and outlet sections of heat exchange tubes
  • Pitting  corrosion throughout a heat exchange tube.

 Contact or crevice corrosion usually develops around an expanded joint. In heat exchangers with steel tube sheets and copper alloy cooling water tubes, corrosion mostly affects the steel tube sheet areas around the tubes. This kind of corrosion damage is accompanied by a strong inflow of cooling water.

 The use of METACOR-VICOR technology and system is an efficient method of corrosion protection and renewal of units affected by this kind of corrosion damage, valid for heat exchangers with both expanded and welded tube joints and all relevant combinations of structural materials.

 Corrosion damage to be found on the inside of the inlet and outlet sections of heat exchange tubes mostly concentrates in their end segments, up to 250 mm (rarely up to 500 mm) from the tube sheet face.

 ROCOR offers technology and compositions ensuring reliable renewal and anticorrosive protection of damaged inlet and outlet sections of heat exchange tubes, tube sheets and water boxes. The principal end result is that by way of renewing inlet sections of heat exchange tubes, cooling water inflow is reduced by 80-95 %; 40-70 % of tubes that had to be shut down become serviceable again; conditions for ball cleaning become ideal.

 VICOR coatings are abrasion- and shock-resistant under standard operational conditions of heat exchange equipment. The coatings are very smooth, which prevents scale formation on the coated inlet and outlet sections of heat exchange tubes.

 When used inside tubing, METACOR-VICOR coatings are not destroyed by high-pressure water jetting usually used to clean heat exchange tubing, and are resistant to all environments and modes of acid cleaning.

 Removal of water from water boxes for long periods, required for periodic maintenance inspection, does not cause cracking or peeling of  METACOR-VICOR coatings.

 The use of optimal technologies, high quality materials and custom developed equipment combined with ample experience of work organization make it possible to repair even the largest heat exchangers quickly and with requisite quality (over 80,000 tubes in 25 days). Anticorrosion protection and renewal of heat exchangers is highly cost effective.

For instance, hermetic encapsulation of the inlet and outlet sections of tubing and anticorrosion protection of tube sheets with the VICOR coatings and technologies at the South Ukraine nuclear power plant has resulted in an increase of electricity output totaling 42.5 million KWh over 10 months. As a result of similar measures having been taken at the bottoming cycle cogeneration plant of the Severstals  power plant, the power output in the condensation mode has grown by 8 per cent.

 

Initial condition of the forward tube sheets of condensers and heat exchangers of a 1000 MW generating unit at a nuclear power plant

  

Coated tube sheets, inlet and outlet sections of heat exchange tubes of a condenser at a nuclear power plant

 HEAT EXCHANGE TUBING. FILLING PITS AND HOLES THROUGHOUT A HEAT EXCHANGE TUBE

 Pitting is an extremely dangerous form of heat exchange equipment corrosion. In case of pitting, corrosion hotspots are randomly distributed throughout a heat exchange tube. The most common reason for this development is poultice and biological corrosion occurring under both hard carbonate deposits and argillaceous sediments.

 A traditional remedy against the inflow of cooling water caused by penetrating corrosion pits in heat exchange tubes has been to shut down the tubes affected. However, whilst solving the immediate problem of water inflow prevention, this induces further disintegration of adjacent heat exchange tubes.

 The following fundamental conclusions have been drawn from inspection of tubing affected by pitting:

  • Corrosion-damaged areas, including deep corrosion pits and through holes, total less than 1 per cent of the aggregate heat transfer surface.
  • Corrosion damage, including through holes, tends to be randomly distributed over a tube.
  • For the most part (about 99 per cent), the surface of a heat exchange tube remains quite serviceable.

Anticorrosion protection and renewal of tubes so damaged will require a tailor-made approach.

   a

   b

This photo shows areas of cleaned interior surface of a heat exchange tube made of COPPER-NIKEL alloy, part of a 1,000 MW generating unit, featuring clusters of corrosion pits (a) and isolated pits (b).

 We have developed a new technology and device for covering pitting-damaged interior surface of heat exchange tubes with polymer coatings and have had them protected with a patent of the Russian Federation (Patent No. 2186633, Heat Exchange Tubing Renewal and Anticorrosion and Scaling Protection Method and Appliance).

 The anticorrosion protection and renewal of condenser or heat exchanger tubing includes the following stages:

  • Preliminary spot inspection of the initial condition of heat exchange tubes with the help of an endoscope
  • Cleaning of tubes from scales and sedimentation
  • Cleaning and surface preparation quality control
  • Surface priming
  • Application of VICOR-TT anticorrosion protection and renewal coating throughout the inside of the heat exchange tube
  • Coating quality control

 It takes about 4 minutes to apply coating to a 9-meter tube. Efficient work organization makes it possible to process up to 2,000 tubes a week with a single unit. In case of large condensers, several units are used simultaneously.

 This technique makes it possible to prolong the service life of operational tubes and recommit 60-90 per cent of those previously shut down. The VICOR-TT polymer coatings that we use feature high thermal conductivity and do not reduce heat transfer efficiency; feature strong and stable adhesion to copper and brass surfaces; and prevent scale formation. This is borne out by the results of this repair techniques industrial application. The proposed solution is 5 to 10 times cheaper than the traditional replacement of tubes.

   

An axial inside view of a tube covered with VICOR-8093-TT coating.

   

A cross-section of a heat exchange tube covered with VICOR-8093-TT coating. Plastic rivets made of VICOR-8093-TT coating are to be seen in the tube walls.

  

A cross-section of a heat exchange tube wall. A corrosion pit is filled with VICOR-8093-TT coating.

   

A cross-section of a heat exchange tube wall. A through corrosion pit is filled with VICOR-8093-TT PLASTIC RIVET coating.

 

WATER BOXES AND WATER DUCTS

It is impossible to deal with clogging and prevent scale formation in heat exchange tubing without preventing intensive formation of corrosion products on the walls of water boxes and circulation water ducts. Technologies developed by ROCOR make it possible to arrange for efficient zonal coating of large surfaces, even where their moistness is higher than required.

 VICOR coatings are resistant to abrasive wear when exposed to water-sand slurry moving at speeds of up to 12 m/s. The coated surfaces being exceedingly smooth, flow resistance is reduced and formation of clam colonies prevented.

 

 

 
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