ANALYSIS OF CAUSES OF EROSIVE DAMAGE TO ELEMENTS OF LOW-PRESSURE EVAPORA+ ON CIRCUITS (LPE) OF CCGT BOILERS

As the operating experience shows, a large number of cases of damage of natural gas pipes with natural and forced circulation are observed at domestic and foreign CCGTs. Basically, the damage is caused by the thinning of the wall of metal tubing bends.

In a number of studies, the thinning of the metal of the bends of the low-pressure evaporator (LPE) pipes is explained by high-speed corrosion (FAC) and droplet-erosion. The intensity of FAC depends on the flow velocity, water temperature, wall material, water-chemical regime (WCR), and the LPE design. Unfortunately, published papers provide no specific recommendations on selection of optimal flow parameters, pipe material, or the optimal boiler water-chemical mode.

On the basis of the experience obtained, the causes of erosion wear of metal tubing bends of evaporation heating surfaces are determined.

Analysis of damage to bends shows the presence of dependency of erosive thinning of the pipe wall on the speed of the steam-water mixture.

The damage to the evaporative tubes of the LPE is caused by destruction of the oxide protective film on the inner surface of the pipes, due to intense turbulence of the wall layer of water flowing in the bend having a saturation temperature, which causes cavitation due to formation of vapor bubbles and their condensation. The aforesaid mechanism of damage is confirmed by the absence of erosion wear of metal on concave and straight sections of pipes, as well as the absence of similar phenomena in the circuits of the medium pressure evaporator and high pressure evaporator of waste heat boilers.

The protective oxide film formed during the hydrate water-chemical mode is characterized by the highest sustainability. 

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