Експериментальне оцінювання механічних властивостей металу трубопроводу зі сталі 17Г1С–У після тривалої експлуатації

Abstract

Наведено результати експериментального визначення характеристик короткочасної статичної міцності та пластичності металу трубопроводу з поздовжнім заводським зварним швом. Встановлено, що характеристики міцності та пластичності основного металу трубопроводу та металу зварного шва залежать від напрямку прокату та форми лабораторних зразків. Визначення характеристик міцності металу трубопроводу неруйнівним методом інструментованого індентування добре узгоджуються з даними механічних випробувань.

The results are presented for the experimental determination of the short-term static strength and ductility of the metal in the longitudinal and transverse directions of the pipe of steel 17G1S-U with a factory-made longitudinal welded joint after a long operation. Specimen blanks were cut out of a piece of the pipe of 530 x 8 mm in diameter. The mechanical properties of the base metal (BM) and the metal in the specific areas of the welded joint: weld metal (WM) and the metal of the heat-affected zone (HAZ) were determined in the transverse direction of the pipe. The mechanical properties of the BM and WM were determined in the longitudinal direction of the pipe. The strength and plasticity characteristics of the pipe metal were determined by conventional tensile testing of laboratory specimens and a nondestructive instrumented indentation technique. For conventional tensile tests, flat specimens (with a treated and untreated test portion), both full-sized cylindrical specimens and those with a shortened test portion (for weld zones) were used. The strength characteristics of the BM were determined by a nondestructive instrumented indentation technique, whereas the strength of the specific areas of the welded joint was determined under static and cyclic loading conditions using a ball indenter of D = 2.5 mm. It is found that the mechanical treatment of both surfaces of the flat specimen of the BM increases the ultimate strength by 4.8%, the offset yield stress by 7.6% and the reduction of area by 16% as compared to the specimen with an untreated surface. The machining of the external or internal surface of the flat specimen increases the ultimate strength only by 1.2% as compared to that with an untreated surface. Tensile tests of specimens with a treated surface (flat and cylindrical specimens) of the BM and WM give a higher ultimate strength (by 6.3-7.6%) as compared to the similar data obtained for flat specimens having the BM without surface treatment, regardless of the rolling direction. The data obtained in testing of cylindrical specimens cut out in the transverse direction of the pipe and having a shortened test portion for the BM and WM exhibit higher ultimate strength and offset yield stress (by 5.46% and 2.86% and 8.7% and 9.05%) and lower reduction of area by 11.42% and 14.42% as compared to the corresponding characteristics obtained for full-sized cylindrical specimens in the longitudinal direction of the pipe. The determination of the strength characteristics of the pipeline metal by a nondestructive instrumented indentation technique agrees well with the data of conventional mechanical tests.