RU2229524C2 - Method to increase resistance of pipes to corrosion and mechanical attacks - Google Patents

Abstract

FIELD: production of pipes resistant to action of attacks of different corrosion factors and mechanical destruction. SUBSTANCE: the invention presents a method allowing to increase resistance of pipes against corrosion and mechanical attacks and is dealt with production and utilization of such pipes in the systems exposed to action of corrosion and mechanical effects. The technical result is achieved by formation on the pipes surfaces of residual squeezing voltages increasing the pipes resistance against corrosion-mechanical shattering. The purpose is achieved by heating of pipes with the joule heat and with simultaneous cooling their surfaces by a cooling agent. After refrigeration and alignments of temperatures along thickness of walls, the residual stresses of squeezing are formed on the pipes surfaces, and in the middle layers of the pipes walls - the residual tensile stresses. As a result resistance of the pipes surfaces against corrosion-mechanical shattering is increased. EFFECT: the invention allows to increase the pipes resistance against corrosion-mechanical shattering. 2 ex

Description

The invention relates to the field of production and use of pipes in systems experiencing the effects of various corrosion factors and mechanical stresses.

Residual (internal) stresses always occur in the walls of pipes made, the level, nature of distribution and the degree of heterogeneity of which is determined by the modes of technologies used in the manufacture, including additional residual stresses from straightening and calibration of pipes (Gudermon E. Special steels. Edited by Zaimovsky A . S. and Bernshtein M.L. - M .: GNTI literature on ferrous and non-ferrous metallurgy, 1959, v. 1, p. 349-366, fig. 287).

The level, nature of the distribution and the degree of heterogeneity of the residual stresses in the pipes can accelerate or slow down the processes of corrosion-mechanical failure in them. In this case, the residual compressive stress slows down, the residual tensile stress accelerates these processes (Nietzsche K. Testing of metals. - M .: Metallurgy, 1967, p. 254).

It is known to use heat treatment technologies to reduce the level of residual stresses.

A known method, including normalization and tempering (Zhukov A.P., Malakhov A.I. Fundamentals of metal science and the theory of corrosion. - M.: Higher school, 1991, p.111-112 and p.37-42). The disadvantages of normalization and tempering are limited opportunities to reduce the level of residual stresses, the uneven nature of their distribution over surfaces and wall thicknesses, and residual deformations along the cross section and length of the pipes.

Closest to the invention is a known method of increasing the resistance of pipes against corrosion and mechanical damage, including the formation of residual compressive stresses on the surface of the pipes by heating with Joule heat and cooling the inner and outer surfaces with a cooling agent (see SU 1680785 A1, IPC 7 C 21 D 9 / 08/30/1991).

This analogue does not provide the formation of a directed (desired) residual stress-strain state of the pipes.

The technical result of the invention is to control the processes of formation of the residual stress-strain state of the pipes, providing increased resistance of pipes against corrosion and mechanical damage.

To achieve a technical result in the known method of increasing the resistance of pipes to corrosion-mechanical destruction, including the formation of residual compressive stresses on the surface of the pipes by heating with Joule heat and cooling the inner and outer surfaces with a cooling agent, the pipe is heated simultaneously with cooling of its surfaces.

Example 1 implementation will explain first, for example, in relation to tubing (tubing) made of medium-carbon, low alloy steel grades. The pipe, designed to reduce residual tensile stresses on its surfaces and compressive, is equipped with current collectors at the ends, through which a current is passed to heat the pipe. The cooling of the surface of the pipe walls can be carried out simultaneously with heating by natural convection of the environment or forced (artificial) convection of a liquid or gaseous cooling agent. Thus, the pipe is heated and the surfaces are simultaneously cooled. The pipe is heated from the internal volume of the walls in the directions to the inner and outer surfaces. In this case, the arising temperature fields along the pipe wall thickness are characterized by a higher temperature of internal volumes (not having the possibility of convective heat exchange with the environment) as compared to near-surface volumes. The difference in temperature along the wall thickness leads to different longitudinal and tangential temperature elongations in the volumes along the wall thickness of the pipe. This circumstance is the cause of the occurrence of stresses of different sign and magnitude that cause deformations in microvolumes. To keep the basic strength characteristics (tensile strength and yield strength) unchanged, the maximum temperature of the pipe heating should not cause changes in the crystal lattice of steel, i.e. must not exceed the maximum possible high tempering temperature for the material of specific pipes. Other circumstances affecting the magnitude and signs of the residual stresses are the intensity of the Joule heat and the cooling rate. After cooling the pipes, i.e. after the temperature is equalized to the wall thickness, the residual deformations in the microvolumes that occur during heating with simultaneous cooling of the surfaces will cause a decrease in the residual tensile stresses and the appearance of residual compressive stresses from the side of the pipe wall surfaces. In this case, residual tensile stresses will appear in the internal volumes along the wall thickness of the pipes to balance near-surface compressive stresses. The proposed technology is especially effective for welded pipes in which the residual stresses and unpredictable directions are especially high along the entire length and thickness of the seams and zones of their thermal influence, and which cannot be eliminated by known methods, including and heat treatment.

It is possible to implement a method of increasing the resistance of pipes against mechanical corrosion in pipelines. In such cases, the method is also carried out by heating sections of the pipeline (pipes and assembly butt welds) through the current collectors with Joule heat while cooling the surfaces by the methods mentioned above.

Example 2

The pipe, designed to form residual compressive stresses on its surfaces, is equipped with satellites, including current collectors located near the ends at both ends and designed to heat the pipes with Joule heat, pipes for pumping a cooling agent through the pipe’s interior, temperature sensors, etc. R. To allow cooling of the outer surface, the pipe is placed in a container with a cooling agent. The tube is heated by Joule heat simultaneously with cooling: the inner surface is pumped by a cooling agent, and the outer surface is cooled by a cooling agent in the tank.

Thus, the present invention allows in the process of heating with Joule heat and simultaneous cooling of the surfaces to create temperature gradients along the thickness of the walls of the pipes, and after heating and complete cooling of the pipes to form on their surfaces (internal and external) residual compressive stresses that increase the resistance of pipes against corrosion-mechanical destruction.

Claims (1)

A method of increasing the resistance of pipes to corrosion-mechanical destruction, including the formation of residual compressive stresses on the surface of the pipes by heating with Joule heat and cooling the inner and outer surfaces with a cooling agent, characterized in that the pipe is heated simultaneously with cooling of its surfaces.