Assessment of residual stresses and post weld heat treatment in butt weld joints of 2.25 Cr1Mo steel tubes by x-ray diffraction technique and Barkausen noise analysis

High Strength Low Alloy (HSLA) steels are the materials of choice in pipeline construction with the API X70 grade as the steel for the majority of pipeline networks constructed during the late 20th and early this century. This paper reports on the influence of Post-Weld Heat Treatment (PWHT) on the reduction of residual stresses, resulting changes in the microstructure, and mechanical properties of a multi-pass, X70 HSLA steel, weld joints made by a combined Modified Short Arc Welding (MSAW) and Flux Cored Arc Welding (FCAW) processes. Neutron diffraction results highlighted high magnitude of tensile residual stresses, in excess of yield strength of both parent and weld metal, in the as-welded specimen (~650 MPa), which were decreased substantially as a result of applying PWHT (~144 MPa). Detailed microstructural studies are reported to confirm the phase transformation during PWHT and its interrelationship with mechanical properties. Transmission Electron Microscopy (TEM) analysis showed polygonization and formation of sub-grains in the PWHT specimen which justifies the reduction of residual stress in the heat-treated weld joints. Furthermore, microstructural changes due to PWHT justify the improvement in ductility (increase in the elongations) with a slight reduction in yield and tensile strength for the PWHT weld joint.

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X-ray Determination of Compressive Residual Stresses in Spring Steel Generated by High-Speed Water Quenching

Materials ◽

10.3390/ma12071154 ◽

2019 ◽

Vol 12 (7) ◽

pp. 1154

Author(s):

Diego E. Lozano ◽

George E. Totten ◽

Yaneth Bedolla-Gil ◽

Martha Guerrero-Mata ◽

Marcel Carpio ◽

...

Keyword(s):

Heat Treatment ◽

Residual Stresses ◽

High Speed ◽

Spring Steel ◽

X Ray Diffraction ◽

Laboratory Equipment ◽

X Ray ◽

Water Chamber ◽

Hardened Case ◽

Compressive Residual Stresses

Automotive components manufacturers use the 5160 steel in leaf and coil springs. The industrial heat treatment process consists in austenitizing followed by the oil quenching and tempering process. Typically, compressive residual stresses are induced by shot peening on the surface of automotive springs to bestow compressive residual stresses that improve the fatigue resistance and increase the service life of the parts after heat treatment. In this work, a high-speed quenching was used to achieve compressive residual stresses on the surface of AISI/SAE 5160 steel samples by producing high thermal gradients and interrupting the cooling in order to generate a case-core microstructure. A special laboratory equipment was designed and built, which uses water as the quenching media in a high-speed water chamber. The severity of the cooling was characterized with embedded thermocouples to obtain the cooling curves at different depths from the surface. Samples were cooled for various times to produce different hardened case depths. The microstructure of specimens was observed with a scanning electron microscope (SEM). X-ray diffraction (XRD) was used to estimate the magnitude of residual stresses on the surface of the specimens. Compressive residual stresses at the surface and sub-surface of about −700 MPa were obtained.

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Residual Stress State of X65 Pipeline Girth Welds Before and After Local and Furnace Post Weld Heat Treatment

Journal of Pressure Vessel Technology ◽

10.1115/1.4035884 ◽

2017 ◽

Vol 139 (4) ◽

Cited By ~ 5

Author(s):

Yao Ren ◽

Anna Paradowska ◽

Bin Wang ◽

Elvin Eren ◽

Yin Jin Janin

Keyword(s):

Heat Treatment ◽

Residual Stress ◽

Residual Stresses ◽

Outer Surface ◽

Post Weld Heat Treatment ◽

Pipe Length ◽

Stress Profiles ◽

Girth Welds ◽

Welded Pipe ◽

Weld Heat

This research investigated the effects of global (in other words, furnace-based) and local post weld heat treatment (PWHT) on residual stress (RS) relaxation in API 5L X65 pipe girth welds. All pipe spools were fabricated using identical pipeline production procedures for manufacturing multipass narrow gap welds. Nondestructive neutron diffraction (ND) strain scanning was carried out on girth welded pipe spools and strain-free comb samples for the determination of the lattice spacing. All residual stress measurements were carried out at the KOWARI strain scanning instrument at the Australian Nuclear Science and Technology Organization (ANSTO). Residual stresses were measured on two pipe spools in as-welded condition and two pipe spools after local and furnace PWHT. Measurements were conducted through the thickness in the weld material and adjacent parent metal starting from the weld toes. Besides, three line-scans along pipe length were made 3 mm below outer surface, at pipe wall midthickness, and 3 mm above the inner surface. PWHT was carried out for stress relief; one pipe was conventionally heat treated entirely in an enclosed furnace, and the other was locally heated by a flexible ceramic heating pad. Residual stresses measured after PWHT were at exactly the same locations as those in as-welded condition. Residual stress states of the pipe spools in as-welded condition and after PWHT were compared, and the results were presented in full stress maps. Additionally, through-thickness residual stress profiles and the results of one line scan (3 mm below outer surface) were compared with the respective residual stress profiles advised in British Standard BS 7910 “Guide to methods for assessing the acceptability of flaws in metallic structures” and the UK nuclear industry's R6 procedure. The residual stress profiles in as-welded condition were similar. With the given parameters, local PWHT has effectively reduced residual stresses in the pipe spool to such a level that it prompted the thought that local PWHT can be considered a substitute for global PWHT.

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Numerical Simulation of Local Post Weld Heat Treatment by Electric Heating Method of Pressure Equipment

Volume 1B: Codes and Standards ◽

10.1115/pvp2017-65695 ◽

2017 ◽

Author(s):

Liang Sun ◽

Fang Ji ◽

Xiaomei Wang ◽

Guide Deng ◽

Lei Cheng

Keyword(s):

Numerical Simulation ◽

Heat Treatment ◽

Wall Temperature ◽

Electric Heating ◽

Post Weld Heat Treatment ◽

Welding Residual Stress ◽

Band Width ◽

Butt Weld ◽

Heating Method ◽

Weld Heat

The local post weld heat treatment by electric heating method is widely used to eliminate welding residual stress in processes of manufacture and maintenance of pressure equipment. The key point of local post weld heat treatment is to choose a reasonable heated band width and insulated band width. But the criterions to determine the minimum heated band width and insulated band width are different according to Chinese, European and American standards, which are GB/T 30583-2014, EN 13445-4: 2009 and AWS D10.10/D10.10M :1999, respectively. Taking the local post weld heat treatment for the circumferential butt weld between two thick cylinders both with a 115 mm thickness as an example, numerical simulation is used to compare the wall temperature distribution of the cylinders during the heat preservation stage when the heated band width and insulated band width are chose according to the above three standards, and the numerical simulation was verified by the tested temperature from one field experiment. The results show that the numerical calculation method can accurately predict the wall temperature of the cylinders during the local heat treatment, and the wall temperature of the surfaces on which the heaters are arranged according to the three standards all well meets the requirement of the heat treatment, but the wall temperature of the surfaces without the heaters cannot meet the temperature requirement. So double-side heating and double-side insulating are suggested to be adopted during local post weld heat treatment.

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Investigation of Residual Stress/Strain and Texture in a Large Dissimilar Metal Weld Using Synchrotron Radiation and Neutrons

Materials Science Forum ◽

10.4028/www.scientific.net/msf.772.193 ◽

2013 ◽

Vol 772 ◽

pp. 193-199 ◽

Cited By ~ 1

Author(s):

Carsten Ohms ◽

Rene V. Martins

Keyword(s):

Synchrotron Radiation ◽

Neutron Diffraction ◽

Residual Stresses ◽

Large Scale ◽

High Energy ◽

X Ray Diffraction ◽

Butt Weld ◽

X Ray ◽

Component Size ◽

Thin Slice

Bi-metallic piping welds are frequently used in light water nuclear reactors to connect ferritic steel pressure vessel nozzles to austenitic stainless steel primary cooling piping systems. An important aspect for the integrity of such welds is the presence of residual stresses. Measurement of these residual stresses presents a considerable challenge because of the component size and because of the material heterogeneity in the weld regions. The specimen investigated here was a thin slice cut from a full-scale bi-metallic piping weld mock-up. A similar mock-up had previously been investigated by neutron diffraction within a European research project called ADIMEW. However, at that time, due to the wall thickness of the pipe, stress and spatial resolution of the measurements were severely restricted. One aim of the present investigations by high energy synchrotron radiation and neutrons used on this thin slice was to determine whether such measurements would render a valid representation of the axial strains and stresses in the uncut large-scale structure. The advantage of the small specimen was, apart from the easier manipulation, the fact that measurement times facilitated a high density of measurements across large parts of the test piece in a reasonable time. Furthermore, the recording of complete diffraction patterns within the accessible diffraction angle range by synchrotron X-ray diffraction permitted mapping the texture variations. The strain and stress results obtained are presented and compared for the neutron and synchrotron X-ray diffraction measurements. A strong variation of the texture pole orientations is observed in the weld regions which could be attributed to individual weld torch passes. The effect of specimen rocking on the scatter of the diffraction data in the butt weld region is assessed during the neutron diffraction measurements.

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The BWR RPV Internals Management Program of the German NPP Gundremmingen, Units B and C: Results and Conclusions

Selected Topics on Aging Management, Reliability, Safety and License Renewal ◽

10.1115/pvp2002-1373 ◽

2002 ◽

Cited By ~ 1

Author(s):

Martin Widera

Keyword(s):

Heat Treatment ◽

Crack Initiation ◽

Residual Stresses ◽

Surface Condition ◽

Management Program ◽

Post Weld Heat Treatment ◽

Interim Result ◽

The Core ◽

Weld Heat ◽

Core Shroud

Due to the core shroud cracks reported from numerous BWRs including the German KWU type BWR Wuergassen, a RPV internals management program for the Gundremmingen NPP (KRB-II) has been initiated in 1994. Major steps and the main results of this program are presented. As an interim result, surface condition of the weld regions and controlled post weld heat treatment (PWHT) in order to reduce the residual stresses seem to play an important role for resistance to crack initiation and growth. To support these assumptions, results of related R&D projects of the German utilities (VGB) are presented.

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