The stress state study of mechanically inhomogeneous welded joints of trunk pipelines with a surface crack-like defect

UDK: 621.643
DOI: 10.24887/0028-2448-2021-5-122-126
Key words: stress state, bearing capacity, mechanical inhomogeneity, welded joint, low-alloy steel, crack-like defect, strength calculation
Authors: E.A. Tigulev (Pipeline Transport Institute LLC, RF, Moscow), I.F. Kantemirov (Ufa State Petroleum Technological University, RF, Ufa), A.A. Raspopov (Pipeline Transport Institute LLC, RF, Moscow), M.Z. Yamilev (Pipeline Transport Institute LLC, RF, Moscow)

The article considers the influence of mechanical inhomogeneity and crack-like defects on the stress state of welded joints (on the example of welded joints of trunk pipelines made of low-alloy steels). Analysis of the results of previously performed studies and existing calculation methods shows that taking into account the features of zones of mechanical inhomogeneity when assessing the bearing capacity of welded joints requires further study. The development of approaches to take into account the geometry of mechanical inhomogeneity will make it possible to assess more reasonably the degree of danger of crack-like defects depending on their location in the welded joint. The determination of the geometry of mechanical inhomogeneous zones was carried out by measuring the hardness indicators. The presented results of experimental studies show the distribution of mechanical characteristics in welded joints. The results of tensile tests of specimens with an applied surface crack-like defect in mechanical inhomogeneous zones of welded joints are presented. It is shown that the difference in the values of the strength parameters of welded joints with different defect locations reaches 10%.The obtained experimental data made it possible to create a mathematical model for determining the values of the critical stresses of welded joints, taking into account the geometry of the zones of mechanical inhomogeneity. The mathematical model is based on a combination of Prandtl's solution on the constancy of tangential stresses along the plastic strip together with the method for finding the stress discontinuity, which makes it possible to take into account edge effects at free boundaries and boundaries of zones of mechanical inhomogeneity. Comparison of the results of the calculated assessment of the strength of mechanically inhomogeneous welded joints with a crest-like defect and experimental data showed their high convergence and confirmed the reliability of the proposed model.

References

1. Tigulev E.A., Yamilev M.Z., Faktory, vliyayushchie na formirovanie slozhnoy topografii mekhanicheskoy neodnorodnosti v svarnykh soedineniyakh uglerodistykh i nizkolegirovannykh staley (Factors influencing the formation of complex topography of mechanical heterogeneity in welded joints of carbon and low-alloy steels), Collected papers “Truboprovodnyy Transport – 2020” (Pipeline Transport - 2020), Proceedings of XV International educational, scientific and practical conference, Ufa: Publ. of USPTU, 2020, pp. 203–205.

2. Neganov D.A., Makhutov N.A., Zorin N.E., Formation of requirements to reliability and security of the exploited sections of the linear part of trunk pipelines transportation of oil and oil products (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2019, no. 6, pp. 106-112.

3. Neganov D.A., Zorin E.E., Zorin N.E., Assessment of influence of surface crack-like stress concentrators on main pipeline operability (In Russ.), Nauka i tehnologii truboprovodnogo transporta nefti i nefteproduktov = Science & Technologies: Oil and Oil Products Pipeline Transportation, 2021, V. 11, no. 1, pp. 8–15.

4. Yamilev M.Z., Tigulev E.A., Yushin A.A. et al., Evaluating mechanical heterogeneity of pipelines welded joints (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2020, no. 11, pp. 128–131.

5. Yamilev M.Z., Tigulev E.A., Raspopov A.A., The assessment of the level of local strengthening of pipe steel welded connections (In Russ.), Nauka i tehnologii truboprovodnogo transporta nefti i nefteproduktov = Science & Technologies: Oil and Oil Products Pipeline Transportation, 2020, V. 10, no. 3, pp. 252–262.

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

7. Dil'man V.L., Research of the mathematical models of the stress condition of the thin-walled heterogeneous cylindrical shells based on analytical methods (In Russ.), Vestnik YuUrGU, 2009, no. 17(150), pp. 36–58.

8. 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.

9. Adaskin A.M., Zuev V.M., Materialovedenie (metalloobrabotka) (Materials science (metalworking)), Moscow: Akademiya Publ., 2009, 288 p.

The article considers the influence of mechanical inhomogeneity and crack-like defects on the stress state of welded joints (on the example of welded joints of trunk pipelines made of low-alloy steels). Analysis of the results of previously performed studies and existing calculation methods shows that taking into account the features of zones of mechanical inhomogeneity when assessing the bearing capacity of welded joints requires further study. The development of approaches to take into account the geometry of mechanical inhomogeneity will make it possible to assess more reasonably the degree of danger of crack-like defects depending on their location in the welded joint. The determination of the geometry of mechanical inhomogeneous zones was carried out by measuring the hardness indicators. The presented results of experimental studies show the distribution of mechanical characteristics in welded joints. The results of tensile tests of specimens with an applied surface crack-like defect in mechanical inhomogeneous zones of welded joints are presented. It is shown that the difference in the values of the strength parameters of welded joints with different defect locations reaches 10%.The obtained experimental data made it possible to create a mathematical model for determining the values of the critical stresses of welded joints, taking into account the geometry of the zones of mechanical inhomogeneity. The mathematical model is based on a combination of Prandtl's solution on the constancy of tangential stresses along the plastic strip together with the method for finding the stress discontinuity, which makes it possible to take into account edge effects at free boundaries and boundaries of zones of mechanical inhomogeneity. Comparison of the results of the calculated assessment of the strength of mechanically inhomogeneous welded joints with a crest-like defect and experimental data showed their high convergence and confirmed the reliability of the proposed model.

References

1. Tigulev E.A., Yamilev M.Z., Faktory, vliyayushchie na formirovanie slozhnoy topografii mekhanicheskoy neodnorodnosti v svarnykh soedineniyakh uglerodistykh i nizkolegirovannykh staley (Factors influencing the formation of complex topography of mechanical heterogeneity in welded joints of carbon and low-alloy steels), Collected papers “Truboprovodnyy Transport – 2020” (Pipeline Transport - 2020), Proceedings of XV International educational, scientific and practical conference, Ufa: Publ. of USPTU, 2020, pp. 203–205.

2. Neganov D.A., Makhutov N.A., Zorin N.E., Formation of requirements to reliability and security of the exploited sections of the linear part of trunk pipelines transportation of oil and oil products (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2019, no. 6, pp. 106-112.

3. Neganov D.A., Zorin E.E., Zorin N.E., Assessment of influence of surface crack-like stress concentrators on main pipeline operability (In Russ.), Nauka i tehnologii truboprovodnogo transporta nefti i nefteproduktov = Science & Technologies: Oil and Oil Products Pipeline Transportation, 2021, V. 11, no. 1, pp. 8–15.

4. Yamilev M.Z., Tigulev E.A., Yushin A.A. et al., Evaluating mechanical heterogeneity of pipelines welded joints (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2020, no. 11, pp. 128–131.

5. Yamilev M.Z., Tigulev E.A., Raspopov A.A., The assessment of the level of local strengthening of pipe steel welded connections (In Russ.), Nauka i tehnologii truboprovodnogo transporta nefti i nefteproduktov = Science & Technologies: Oil and Oil Products Pipeline Transportation, 2020, V. 10, no. 3, pp. 252–262.

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

7. Dil'man V.L., Research of the mathematical models of the stress condition of the thin-walled heterogeneous cylindrical shells based on analytical methods (In Russ.), Vestnik YuUrGU, 2009, no. 17(150), pp. 36–58.

8. 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.

9. Adaskin A.M., Zuev V.M., Materialovedenie (metalloobrabotka) (Materials science (metalworking)), Moscow: Akademiya Publ., 2009, 288 p.


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