It always made high demands for reliability and safety of chemical enterprise equipment. It is connected therewith that machines and devices operate under heavy conditions: pressure, temperature, corrosive medium. Along with heavy conditions in any equipment a number of processes run which negative influence on the operation life of constructional its elements. It is inadmissible for enterprises in this industry because any failure can lead to depressurization of equipment, emission of harmful and hazardous substances into the atmosphere, will be causing great economic loss, will have a negative effect on the ecological situation and may affect on the population health living near the enterprise.

Currently, the main task is not only decreasing the accident rate of the existing technical object but also to research the problems of engineering environmental. Subject of inquiry is the primary gas cooler (PGC) Avdeyevka by-product coke plant. It is a device with dimensions of 24,7x3,6x3 m, has a capacity of 20,000 m³/ h. All the coke oven gas passes through it with a temperature of 82 - 35 ° C under a pressure of 0,095 MPa. The coke oven gas is fed into pipe space, and chilled (26 ° C) industrial water and soda solution of desulphurization plant (50 ° C) move in pipe space under a pressure of 0,4 MPa. Coke oven gas is a combustible gas, it is explosive in mixed with air (the flammability limit from 6 to 30%) and fire-hazardous (the flammability temperature is 600 - 650 ° C), is toxic. The maximum permissible concentration of its components should not be more (in mg/m³): 300 СН₄, 50 С_mН_n, 5 С₆Н₆, 20 СО, 10 H₂S, 0,3 HCN, 0,3 С₆Н₅ОН, 5 С₅Н₅N.

A whole number of technological processes flows in PGC. First of all, it's heat exchangers, in particular heat transfer from the coke oven gas to the water through a separating wall, which is accompanied by a number of other processes: the condensation of water vapor from the coke oven gas, the condensation and separation of pitch vapor residual, mass transfer. Heat transfer is carried out in pipes, and the temperature of the coke oven gas decrease, so that the liquid phase – the pitch – is escaped from gas and absorbing naphthalene it is formed a complex corrosive substances. The absorption of ammonia, carbon dioxide, hydrogen sulfide, hydrocyanic acid and other components containing in the coke gas happen by the condensation of water on the pipes surface. The combination of different acids is generated, that also promote destruction of the PGC elements.

Degradation processes unavoidable flows along with the technological processes. They are corrosion of casing, the outer and inner surfaces of pipes, scaling, a material aging.

The apparatus casing was subjected to corrosion increasingly. With the outside – chemical (rusting of metal elements under the influence of aggressive medium) and electrochemical (under the influence of rain water and a condensate with the salts ions and acids dissolved in these) corrosion, with the inside – the destruction under the action of aggressive substances in the coke oven gas. The pitch is escaped upon cooling the coke oven gas, it absorbs naphthalene and generate a concentrated alkali, which reacts with the elements of PGC structure and leads to them intensive corrosion. The presence of cyanic hydrogen also accelerates the degradation process of the casing and pipes (Fig. la). HCN dissolves partially in ammonia-tar water with formation of the toxic ammonium salts of cyanide and thiocyanic acids.

Pipes also undergo corrode from the inside under the action of the impurities that are in the industrial water and soda solution. All this leads to the destruction of the metal casing, an arising in the pipes (Fig. lb). The soda solution through an arising will go into the gas condensate, which will have an adverse effect on the operation of mechanized clarifiers, biochemical waste treatment and will complicate of pitch processing. Intensive corrosion of pipes promotes to the accumulation of ballast salts in the soda solution and deterioration its absorption capacity.

Another type of degradation of the PGC elements is the formation of solid deposits on the inner walls of pipes, that is scaling (Fig. 1c). The formation of a layer of scale reduces the flow area of pipes, in so doing their roughness increase and the hydraulic flow regime changes. The thermal conductivity of scale is less in the tens, often hundreds of times than the thermal one of steel, of which is manufactured heat exchangers. This leads to the deterioration of the heat transfer conditions in particular disturbance of the basic technological process. The phenomenon of scale also leads to an increase of turbulence and the significant purification costs of pipe.

Figure 1 - Types of pipes degradation in the primary gas cooler:
a - chemical corrosion, b – an arising; c – scale

Ageing processes (degradation of the structure and the mechanical properties) flows actively to the metal under the influence of high temperature, pressure, corrosive medium, as well as subject to the continuous operation of equipment. It adversely affect the strength of elements of equipment and may be cause its accidental destruction.

After analyzing the above, it may be noted that the primary gas cooler is complicated equipment by the operation. It operated in hostile mediums and gradually ruptured in consequence of the complex processes operating, both technological and degradation. It brings not only great economic losses, but increases the failures and accidents risk and deterioration of ecological situation. Ensuring safe operation conditions and service-life extension of the given apparatus is very actual.