RT - Journal Article T1 - Investigation of weldability in multi-pass girth welding of thermomechanical steel pipe JF - mdrsjrns YR - 2013 JO - mdrsjrns VO - 13 IS - 4 UR - http://mme.modares.ac.ir/article-15-7769-en.html SP - 60 EP - 73 K1 - API X70 K1 - Girth Weld K1 - Thermomechanical Steel K1 - Steel Pipe K1 - Natural Gas Transmission K1 - API X70 AB - The structural integrity of welded joints in natural gas transportation through large diameter steel pipes requires the experimental determination of material mechanical properties in seam weld via destructive and non-destructive testes. In this paper, the metallurgical and mechanical characteristics of multi-pass girth weld in seam weld, heat affected zone (HAZ), and base metal of a pipe with 56 inch outside diameter, 0.780 inch wall thickness is determined. To do this, chemical analysis, standard metallography, tensile and impact tests and hardness experiments were conducted. The metallographic results demonstrated that different sub-zones in welded joint had different microstructure. The existence of different chemical contents in different weld passes and the presence of hard phases (such as martensite due to uncontrolled heat cycles) had direct effects on mechanical properties of the seam weld and HAZ. From the hardness test result, it was found that HAZ and centerline of the seam weld had the minimum and maximum hardness levels, respectively. Furthermore, the minimum Charpy impact energy was found in the seam weld centerline. LA eng UL http://mme.modares.ac.ir/article-15-7769-en.html M3 ER -