Supervisor of master's dissertation is Shtyhno A.P.

THE IMPROVEMENTS OF THE COMPLEX CHARACTERISTIC OF WELDED SEAM OF PIPES WITH LOCAL DEFORMATION THERMAL PROSSESING (LDTP)
 

 Today large assortment of the pipes is presented on the market of the building materials.  These pipes do not be subjected of the attack of rodent to in contrast with plastic. Presently under significant increase the cost of the gas, has got up the question about transportation strategic fuel on new route gas main. So at the moment construction of modern main oil and gas route is of great importance for our country for achievement of the provision to energy independence and safety of the Ukraine.

The main reason of the nucleation of pipes defect, which cause the destructions of main pipe line at usage is: low quality of the metal, imperfection of technologies of the fabrication, welding. The main defect of the welded pipes remains the presence a stress concentrator in place of the transition from reinforcement of the seam to the main metal, which is a source of possible refusal of the pipe line in critical condition.

Thereby, for reception of the even welded join under arc welding, which provides the minimum leash under the following usage, and for increasing quality of fixings corrosion resisting covering at factory condition it is necessary to obtain accuracy of the geometric sizes of the pipe and homogeneity of the structure on section. All this justifies application of local complex deformation for decision of this task - a thermal processing.

Among the known ways of increasing of quality metal products the most using way is an improvement of the functional features carbon steel - a thermal processing.

The normalization of the welded join can provide certain improvement a characteristic, in consequence of recrystallization and refinement of grain. It perfects micro structure of metal of the seam and zone of the thermal influence, raises toughness of these zones and their stability at low temperature. This processing is rational at heating of the whole product. The local heating for normalization only zones of the welded join can bring about forming the remaining stress of the strain in this zone. Reduce the velocity of the cooling at normalizations is irrational, since this will not allow to provide the effect which we pursue - a refinement of grain.

The high tempering of the welded join of low carbon steel does not change the structured condition of the metal, it is only concluded in reduction of remaining stresses level, which at usages can bring about negative influence on efficiency of construction, also furlough influences on non equilibrium structures, reduction of hardness and increasing of impact toughness. The high tempering can be as local, so and the general, velocity of the cooling after local tempering advisable to limit to reduce the value of the remaining stress in accordance with locality of the heating.

And so as to heat treatment with heating of the whole product that this way requires raised material and energy expenseses. But local heat treatment has a defect - remains the main concentrator of the stress - a reinforcement of the seam.

Dispose of reinforcements of the seam is possible only by means of thermo mechanical of the processing (TMP). TMP presents itself combination of operation of deformation, heating and cooling, as a result which formation of the remaining structure by steels passes in condition of raised density structured imperfection, which were formed during deforming. To imperfection refer dislocation, their structure and grain boundary.

For full removing of negative factor of welded join, optimum will be an use of local thermo mechanical processing or local deformation-thermal processing (LDTP).

Except improvements of the complex characteristic welded joining the pipes of LDTP - will bring about the following important working advantage of the pipes (with rolled out before level of the main wall seam): removing the concentrator of the stress on the whole length of the pipe, which is a seam; the improvement of its conditions of the fixing corrosion resisting covering in zone of the welded join; falls off need in operations of milling of final area pipes; removing area of hake brittleness.

Introduction of local DTP will provide monolith of pipes on section.

Impact toughness of the welded join after LDTP in the centre of the seam and in zone of the thermal influence in all interval of the temperature in 2 times more practically than similar factors before LTMP, and are at a rate of the main metal.
 

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