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Evaluating mechanical heterogeneity of pipelines welded joints

UDK: 621.643
DOI: 10.24887/0028-2448-2020-11-128-131
Key words: welded joint, strength, mechanical characteristics, pipeline, strength calculation
Authors: M.Z. Yamilev (The Pipeline Transport Institute LLC, RF, Moscow), E.A. Tigulev (The Pipeline Transport Institute LLC, RF, Moscow), A.A. Yushin (The Pipeline Transport Institute LLC, RF, Moscow), A.A. Raspopov (The Pipeline Transport Institute LLC, RF, Moscow), I.F. Kantemirov (Ufa State Petroleum Technical University, RF, Ufa)

The existing methods for strength calculating that underpin pipeline design are based on indicators of the strength characteristics of the pipe metal. The presence of a welded joint is taken into account using coefficients characterizing its shape and characteristics of the weld metal. In this case, the weld and the zone of the original metal subjected to the influence of the thermal cycle are assumed to be homogeneous in mechanical properties. However, a change in properties of welded joint affects the overall bearing capacity and is defined by both mechanical and geometric parameters.

In the article, the authors propose to consider an approach to assessing the contact hardening of a welded joint of pipe steels that arise at a certain range of geometric parameters, taking into account the real topographic structure of a circumferential pipeline weld. Based on the results of experimental studies, an assessment of the mechanical characteristics of welded joints of pipe steels is presented, and the geometric features of the formation of the topographic structure are shown. The weld structure was evaluated by measuring the microhardness values. Based on the results of the analysis of the topography of mechanical inhomogeneity, an integral estimate of the dependence is proposed to determine the values of the contact hardening coefficient for curvilinear forms of inhomogeneity fields. Further development of studies of the welded joints structure in pipelines will allow to improve approaches to the calculation of their strength parameters, to develop recommendations for regulating the thermal deformation cycle, taking into account the optimal location of the fields of mechanical heterogeneity; to prepare a scientific justification for assessing the strength characteristics of a weld in the presence of a surface defect, taking into account the relative position of "soft" and "hard" interlayers.

References

1. Bakshi O.A., Mekhanicheskaya neodnorodnost' svarnykh soedineniy (Mechanical heterogeneity of welded joints), Part 1, Chelyabinsk: Publ. of ChPI, 1981, 57 p.

 2. Bakshi O.A., Kul'nevich T.V., Influence of the degree of mechanical inhomogeneity on the ductile strength of welded joints under tension (In Russ.), Fizika i khimiya obrabotki materialov, 1973, no. 1, pp. 23–27

3. Bakshi O.A., Shron R.Z., On the calculated assessment of the strength of welded joints with a soft interlayer (In Russ.), Svarochnoe proizvodstvo, 1971, no. 3, pp. 3–5.

4. Vinokurov V.A., Kurkin S.A., Nikolaev G.A., Svarnye konstruktsii. Mekhanika razrusheniya i kriterii rabotosposobnosti (Welded structures. Fracture mechanics and performance criteria), Moscow: Mashinostroenie Publ., 1996, 576 p.

5.  Neganov D.A., Makhutov N.A., Lisin Yu.V., Varshitskiy V.M., Comprehensive analysis of the pipelines safety and basic mechanical properties of the pipe steels  (In Russ.), Nauka i tehnologii truboprovodnogo transporta nefti i nefteproduktov = Science & Technologies: Oil and Oil Products Pipeline Transportation, 2017, no. 1 (28), pp. 3–38

6. Shakhmatov M.V., Issledovanie vliyaniya konstruktivnykh i geometricheskikh parametrov stykovykh bimetallicheskikh shvov na rabotosposobnost' svarnykh soedineniy (Investigation of the influence of design and geometric parameters of bimetallic butt welds on the performance of welded joints): thesis of candidate of technical science, Moscow, 1979.

The existing methods for strength calculating that underpin pipeline design are based on indicators of the strength characteristics of the pipe metal. The presence of a welded joint is taken into account using coefficients characterizing its shape and characteristics of the weld metal. In this case, the weld and the zone of the original metal subjected to the influence of the thermal cycle are assumed to be homogeneous in mechanical properties. However, a change in properties of welded joint affects the overall bearing capacity and is defined by both mechanical and geometric parameters.

In the article, the authors propose to consider an approach to assessing the contact hardening of a welded joint of pipe steels that arise at a certain range of geometric parameters, taking into account the real topographic structure of a circumferential pipeline weld. Based on the results of experimental studies, an assessment of the mechanical characteristics of welded joints of pipe steels is presented, and the geometric features of the formation of the topographic structure are shown. The weld structure was evaluated by measuring the microhardness values. Based on the results of the analysis of the topography of mechanical inhomogeneity, an integral estimate of the dependence is proposed to determine the values of the contact hardening coefficient for curvilinear forms of inhomogeneity fields. Further development of studies of the welded joints structure in pipelines will allow to improve approaches to the calculation of their strength parameters, to develop recommendations for regulating the thermal deformation cycle, taking into account the optimal location of the fields of mechanical heterogeneity; to prepare a scientific justification for assessing the strength characteristics of a weld in the presence of a surface defect, taking into account the relative position of "soft" and "hard" interlayers.

References

1. Bakshi O.A., Mekhanicheskaya neodnorodnost' svarnykh soedineniy (Mechanical heterogeneity of welded joints), Part 1, Chelyabinsk: Publ. of ChPI, 1981, 57 p.

 2. Bakshi O.A., Kul'nevich T.V., Influence of the degree of mechanical inhomogeneity on the ductile strength of welded joints under tension (In Russ.), Fizika i khimiya obrabotki materialov, 1973, no. 1, pp. 23–27

3. Bakshi O.A., Shron R.Z., On the calculated assessment of the strength of welded joints with a soft interlayer (In Russ.), Svarochnoe proizvodstvo, 1971, no. 3, pp. 3–5.

4. Vinokurov V.A., Kurkin S.A., Nikolaev G.A., Svarnye konstruktsii. Mekhanika razrusheniya i kriterii rabotosposobnosti (Welded structures. Fracture mechanics and performance criteria), Moscow: Mashinostroenie Publ., 1996, 576 p.

5.  Neganov D.A., Makhutov N.A., Lisin Yu.V., Varshitskiy V.M., Comprehensive analysis of the pipelines safety and basic mechanical properties of the pipe steels  (In Russ.), Nauka i tehnologii truboprovodnogo transporta nefti i nefteproduktov = Science & Technologies: Oil and Oil Products Pipeline Transportation, 2017, no. 1 (28), pp. 3–38

6. Shakhmatov M.V., Issledovanie vliyaniya konstruktivnykh i geometricheskikh parametrov stykovykh bimetallicheskikh shvov na rabotosposobnost' svarnykh soedineniy (Investigation of the influence of design and geometric parameters of bimetallic butt welds on the performance of welded joints): thesis of candidate of technical science, Moscow, 1979.



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