Residual Stress Relaxation in a Tube Attachment Weld Inside a Pressure Vessel Forging During Post Weld Heat Treatment

2007 ◽  
Author(s):  
P. R. Hurrell ◽  
J. Davies ◽  
N. A. Leggatt ◽  
R. J. Dennis ◽  
R. H. Leggatt
Keyword(s):  
Heat Treatment ◽  
Residual Stress ◽  
Stress Relaxation ◽  
Pressure Vessel ◽  
Hold Time ◽  
Stress Relief ◽  
Post Weld Heat Treatment ◽  
Secondary Creep ◽  
Axial Tensile ◽  
Weld Heat

This paper presents analyses done to determine residual stress relief achieved by post weld heat treatment (PWHT) of tube attachment welds inside a thick SA508 steel pressure vessel forging. Finite element (FE) analyses were performed modelling the manufacturing operations in detail including welding, machining and PWHT. The analyses demonstrate that PWHT at 600°C for 8 hours is effective in reducing as-welded residual stress levels from tensile yield magnitude (+500MPa approx) to <100MPa. The maximum residual stress was computed to be 90MPa sub-surface in a region of hydrostatic (tri-axial tensile) stress. Secondary creep was modelled using data from creep tests on SA508 steel uni-axial tensile specimens. Practically all of the stress relaxation is due to creep strain with minimal additional plastic strain. Most stress relief occurs during the first hour of soak, with diminishing benefit thereafter. Analysis results also indicate that PWHT effectiveness is more sensitive to soak temperature than hold time. These FE results are considered slightly pessimistic but are reasonably consistent with other analytical predictions. By comparison surface hole drilling stress measurements of <50MPa (10% yield strength) were recorded from a representative welded test block. Analysis pessimism was attributed to ignoring both primary creep and relaxation during the slow warm up phase of the heat treatment cycle.

Finite Element Modelling of a Tube to Vessel Attachment Weld and Local Post-Weld Heat Treatment

2011 ◽  
Author(s):  
Benjamin M. E. Pellereau ◽  
Paul R. Hurrell ◽  
Christopher M. Gill ◽  
Sarah L. Allen
Keyword(s):  
Heat Treatment ◽  
Finite Element ◽  
Pressure Vessel ◽  
Hold Time ◽  
Measurement Data ◽  
Stress Relief ◽  
Post Weld Heat Treatment ◽  
Isotropic Hardening ◽  
Fe Model ◽  
Weld Heat

This paper describes Finite Element (FE) modelling of a weld between a tube and a machined feature on a curved pressure vessel surface. The components were manufactured from a ferritic steel with a matched weld metal deposited by a mechanised TIG process. The weld region then underwent a local Post-Weld Heat Treatment (PWHT) which used heating bands and cooling air flows to control the temperature distribution. The PWHT’s aim was to provide stress relief and HAZ tempering, while minimising the stresses due to thermal gradients in the component. Trial welds on representative test pieces had predicted significant welding-induced distortions. Therefore, during the weld and PWHT, restraints were applied to the tube to prevent excessive deformation. The material behaviour was represented using Abaqus’ built-in material options, with the same properties for both the base metal and the filler. Isotropic hardening was assumed and the stress relaxation during the PWHT was modelled by applying a Norton creep law only during the hold time. Phase transformation effects in the ferritic material were not included. Initial modelling used a 2D axisymmetric model to allow sensitivity studies to inform the development of the PWHT process. These showed that the degree of stress relief was much more sensitive to the soak temperature than the hold time. Subsequent runs analysed a 3D model using a segmented block-dumping technique, with the deposition modelled by introducing the weld elements in 90° segments. The 3D modelling was undertaken in order to more accurately model potentially asymmetric welding distortions and residual stresses. The torch was represented by a body flux into each segment after its introduction. This model was also run without restraint to provide validation by comparing the predicted distortion with measurements from the welding trials; a good match was demonstrated. Further comparisons were made between the predicted stresses and results of Incremental Centre Hole-Drilling (ICHD) stress measurements made on the trial specimens both in the as-welded condition and after PWHT. The measured stresses were close to those predicted by the FE analysis and the key features of the predicted stress field were apparent in the measurement data. Due to the location of the tube’s attachment to the pressure vessel, thermal expansion of the vessel during the PWHT caused the tube to bend. The induced bending stresses were then relaxed during the soak and re-introduced in the opposite sense as the system cooled. This effect was captured by running the analysis as a submodel of a global FE model with displacements read across at nodes in the pressure vessel shell immediately below the weld.

An Arrhenius equation-based model to predict the residual stress relief of post weld heat treatment of Ti-6Al-4V plate

2018 ◽  
Vol 32 ◽  
pp. 763-772 ◽  
Author(s):  
Guangxu Yan ◽  
Alexandru Crivoi ◽  
Yajuan Sun ◽  
Niroj Maharjan ◽  
Xu Song ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Residual Stress ◽  
Arrhenius Equation ◽  
Stress Relief ◽  
Post Weld Heat Treatment ◽  
Weld Heat

Residual Stress Relief in Post-Weld Heat Treatment

2008 ◽  
Author(s):  
Pingsha Dong ◽  
Jeong K. Hong
Keyword(s):  
Heat Treatment ◽  
Residual Stress ◽  
Stress Relief ◽  
Heating Time ◽  
Post Weld Heat Treatment ◽  
Weld Residual Stress ◽  
Pressure Vessel Steels ◽  
Parametric Analyses ◽  
Holding Temperature ◽  
Weld Heat

This paper focuses on analysis of weld residual stress relief process during furnace-based uniform post-weld heat treatment (PWHT). Two classes of pressure vessel steels: 2-1/4CrMo and carbon steel are considered in seam weld configurations. It is found that the dominant mechanism for residual stress relief is the creep relaxation that occurs much earlier during a PWHT cycle than typically expected. This phenomenon is further confirmed by experimental data. After a large number of parametric analyses of various PWHT parameters, a simple form of relationship is proposed for relating residuals stress relief to a set of PWHT parameters for the two classes of steels. These parameters include PWHT ramp-up heating time, PWHT holding time, PWHT holding temperature, and weldment thickness.

scholarly journals Optimization Study of Post-Weld Heat Treatment for 12Cr1MoV Pipe Welded Joint

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 127
Author(s):  
Zichen Liu ◽  
Xiaodong Hu ◽  
Zhiwei Yang ◽  
Bin Yang ◽  
Jingkai Chen ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Residual Stress ◽  
Stress Reduction ◽  
Simulation Method ◽  
Post Weld Heat Treatment ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Tempering Treatment ◽  
Temper Heat Treatment ◽  
Weld Heat

In order to clarify the role of different post-weld heat treatment processes in the manufacturing process, welding tests, post-weld heat treatment tests, and finite element analysis (FEA) are carried out for 12C1MoV steel pipes. The simulated temperature field and residual stress field agree well with the measured results, which indicates that the simulation method is available. The influence of post-weld heat treatment process parameters on residual stress reduction results is further analyzed. It is found that the post weld dehydrogenation treatment could not release residual stress obviously. However, the residual stress can be relieved by 65% with tempering treatment. The stress relief effect of “post weld dehydrogenation treatment + temper heat treatment” is same with that of “temper heat treatment”. The higher the temperature, the greater the residual stress reduction, when the peak temperature is at 650–750 °C, especially for the stress concentration area. The longer holding time has no obvious positive effect on the reduction of residual stress.

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

2017 ◽  
Vol 139 (4) ◽  
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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