Influence of the interpass temperature on the microstructure and mechanical properties of the weld metal (AWS A5.18 ER70S-6) of a narrow gap welded API 5L X70 pipe joint

To reduce manufacturing costs, manufacturers may perform welding with a high interpass temperature (IT), which can reduce the welding idle time and increase the productivity of welding production. However, an increase in IT can jeopardize the behavior of welded joints. Therefore, the present study investigated the effects of high ITs (295, 345, and 390 °C) on the weld metal (AWS A5.18 ER70S-6) of a narrow groove high-strength low-alloy steel (API 5L X70) pipe welded by a gas metal arc. The increase in IT led to a decrease in the welding idle time. The highest ITs (345 and 390 °C) reduced the thermal gradient, thus increasing the cooling time from 800 to 500 °C (t8/5), which enhanced the formation of low-toughness constituents (sideplate and proeutectoid ferrites) and reduced the acicular ferrite content. This induced a drop in the weld metal Charpy V-notch (CVN) impact energy. Nevertheless, even the IT = 390 °C condition (with the lowest CVN impact energy) satisfied the DNVGL-ST-F101 standard requirements, which indicates that a high IT can be used to increase the effective productivity factor and reduce the welding cost. However, it is necessary to evaluate the risk of this decrease in CVN impact energy for each application.