Research on the influence of heat treatment temperature on bearing capacity of high steel grade pipeline during in-service welding

Yan Xu,Jasmine Jasmine,Zhenjun Feng,Xianghui Nie,Liang Li,Yinglai Liu,Fengping Yang,L Liu,F Liu

doi:10.1051/matecconf/202135301020

Abstract

During the welding of in-service pipeline, natural gas is continuously transported in the pipeline, which maintains a high gas pressure. Therefore, the welding process is completed under strong cooling conditions, and welding delay crack is easy to occur. Preheating before welding and heat treatment after welding can effectively control the hardened microstructure, reduce the residual stress and ensure the welding quality. In this study, the influence of heating temperature on the bearing capacity of high steel grade pipe during in-service welding repair was studied. The high temperature tensile test was used to simulate the bearing capacity of the pipe under heating and high temperature environment. It is found that when the heating temperature is below 400°C, the pipe strength remains at the original level. With the increase of heating temperature, when the test temperature is higher than 400°C, the yield strength and tensile strength of the pipe decrease significantly. When the test temperature is 450°C, the yield strength and tensile strength of the material decrease by 15.8% and 11.1%, respectively, compared with the normal temperature, which are lower than the pipe standard requirements. Therefore, it is suggested that when the heat treatment temperature is higher than 400°C during in-service welding repair, it is necessary to consider reducing the pipeline pressure. At the same time, the box furnace heat treatment method was adopted to heat treat the pipe, and the tensile properties of the pipe after heat treatment were tested to analyze the bearing capacity of the pipe after heat treatment. It is found that when the heating temperature is higher than 700°C, the tensile properties of high grade pipeline steel pipe decrease sharply. It is suggested that when the heat treatment temperature is higher than 700°C, the risk assessment of the service safety of the heat treated pipeline should be carried out.

Highlights

In-service welding repair is one of the main repair methods in pipeline defects and leakage repair work
The inservice welding repair technology is faced with two technical difficulties, namely, burn-through and hydrogen-induced cracks [3,4,5,6] Among them, burnthrough mainly considers that the welding arc is instantaneously loaded on the pipe metal in the welding process, and the increases instantaneously
When the test temperature is450°C, the yield strength of the material is 533MPa, the tensile strength is 618MPa, compared with the room temperature tensile properties decreased by15.8% and 11.1%, the value is lower than the standard requirements

Summary

Introduction

In-service welding repair is one of the main repair methods in pipeline defects and leakage repair work. It can ensure the continuous pipeline transportation, and reduce the degree of environmental damage, shorten the repair cycle and reduce the repair cost [1,2]. At present, the mainstream technology of pipeline steel production is to prepare high strength and toughness steel through low-carbon micro-alloying combined with thermo-mechanical control process. It is necessary to study the influence of heat treatment temperature on the bearing capacity of high-grade pipeline during welding of inservice pipelines

Test Materials and Methods

Test result

C NM N r iob e

Conclusion