Creep properties in similar weld joint of a thick-walled P92 steel pipe (original) (raw)
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Creep behavior of P91B steel in the presence of a weld joint
Materials Science and Engineering: A, 2015
The paper presents creep test data on standard P91B steel specimens made from two distinct regions of a welded plate over a range of stresses (50-190 MPa) and temperatures (600-650°C). The analysis of test data revealed that the samples having a weld zone within the gage length (cross-weld samples) have lower long term rupture strength than the samples made of the base metal. Estimated weld strength factors (WSF) of this steel were found to be higher than those reported for P91 steel. The study also showed that the effect of welding on loss of rupture ductility is much more prominent than its effect on the reduction in rupture strength. In presence of welded zone the extent of local deformation in ruptured samples was not as prominent as in the samples without weld. Creep damage tolerance factors (λ) were estimated from the creep strain versus time plots. This also showed that the magnitude of λ is significantly reduced in the presence of welding. Examination of microstructure and measurement of density revealed that this difference is primarily due to the formation of cavities in the heat affected zones of welded specimens. In the lower stress regime a few test specimens without any welded region did not fail even after very long creep exposure. Diameters of these specimens were found to have increased in spite of measureable increase in length due to creep. This unusual effect has been attributed to oxide scale growth. It shows up when the increase in diameter due to the growth of oxide scale becomes greater than the decrease in diameter due to the accumulation of creep strain.
Creep resistance of similar and dissimilar weld joints of P91 steel
Materials at High Temperatures, 2006
Two experimental weld joints, a similar weld joint of 9Cr-1Mo steel and a dissimilar weld joint of 9Cr-1Mo and 2.25Cr-1Mo steels, were fabricated by the TIG þ E method and post-weld heating was applied. Creep testing was carried out at temperatures ranging from 525 to 625 C in the stress range 40-240 MPa. Creep rupture strength was evaluated using the Larson-Miller parameter. Extended metallography including transmission electron microscopy was performed and critical zones were indicated where fractures were concentrated during the creep exposure. At high temperatures rupture of the dissimilar weldment occurred in the heat affected zone (HAZ) of the weld metal while rupture of the similar weldment was located in the HAZ of the parent material. The processes of recovery seem to be the main causes of decrease in creep rupture strength of both weld joints in comparison to the parent materials.
Analysis of the Creep Behavior of P92 Steel Welded Joint
Different regions of heat-affected zone (HAZ) were simulated by heat treatment to investigate the mechanisms of the Type IV fracture of P92 (9Cr-2W) steel weldments. Creep deformation of simulated HAZ specimens with uniform microstructures was investigated and compared with those of the base metal (BM) and the weld metal (WM) specimens. The results show that the creep strain rate of the fine-grained HAZ (FGHAZ) is much higher than that of the BM, WM, the coarse-grained HAZ (CGHAZ), and the inter-critical HAZ (ICHAZ). According to the metallurgical investigation of stress-rupture, the FGHAZ and the ICHAZ have the most severely cavitated zones. During creep process, carbides become coarser, and form on grain boundaries again, leading to the deterioration of creep property and the decline of creep strength. In addition, the crack grows along the FGHAZ adjacent to the BM in the creep crack growth test (CCG) of HAZ.
Creep strength and microstructure of a modified P911-type steel weld joint
IOP Conference Series: Materials Science and Engineering, 2021
The creep strength and microstructure of the weld joint of the modified P911-type steel has been studied. The creep rupture time of the welded joint at 650° of 1375 h is close to that of the base metal. The heat affected zone-is found to be the weakest area due to the increased size and relatively high coarsening rate of precipitates. The increased boron content in the weld steel effectively stabilizes the M23(C,B)6 particles and is beneficial for the creep strength of the weld joint in the fusion zone.
Effect of welding on creep damage evolution in P91B steel
Journal of Nuclear Materials, 2017
Study of creep behavior of base metal (without weld) and welded specimens P91B steel over a range of temperature (600-650 °C) and stress (50-180 MPa) showed similar values of minimum creep-rates for both specimens at higher stress regime (> 100 MPa) whilst, significantly higher creep rates of welded specimens at lower stress regime Considering that welded specimen comprised of two distinct structural regimes, i.e. weld affected zone and base metal, a method was proposed for estimating the material parameters describing creep behavior of those regimes. Stress-strain distribution across welded specimen predicted from finite element analysis based on material parameters revealed preferential accumulation of stress and creep strain at the interface between weld zone and base metal. This is in-line with the experimental finding that creep rupture preferentially occurs at inter-critical heat affected zone in welded specimens owing to ferrite-martensite structure with coarse Cr 23 C 6 particles.
Creep Crack Growth Behavior of a P91 Steel Weld
Procedia Engineering, 2014
Modified 9Cr-1Mo steel (P91) weld joints operating at elevated temperatures are well known to be prone to premature failure due to cracking in the heat affected zone because of the gradients in microstructure, popularly referred to as Type IV cracking. A campaign was undertaken to study the creep crack growth behaviour of modified 9Cr-1Mo weld joints. Creep crack growth (CCG) tests were carried out on compact tension (CT) specimens machined from P91 weld joints prepared using multipass shielded manual metal arc welding procedure. Specimens with two notch locations have been employed, (i) within the weld metal, between the centreline and the fusion line and (ii) in the heat affected zone. Constant load CCG tests were carried out at different applied loads at 798 and 898 K. The C*-da/dt correlations (da/dt =A C *m) were established for both notch locations. At 898 K, a higher A (0.064) and lower m (0.533) for the case with notch placed in the HAZ, compared to those for the case of notch in the weld (0.0399 and 0.75 respectively) were observed indicating the higher creep crack growth in HAZ, confirming type IV cracking. The difference increases at lower C* levels which correspond to long term behaviour. Heavy creep damage was observed in the HAZ region even for the sample with notch in the weld, whereas the weld metal regions showed relatively less damage. As the crack grew, a change in its course to follow the HAZ region was observed.
The Impact of Weld Metal Creep Strength on the Overall Creep Strength of 9% Cr Steel Weldments
Journal of Engineering Materials and Technology, 2011
In this work, three joints of a X11CrMoWVNb9-1-1 (P911) pipe were welded with three filler metals by conventional arc welding. The filler metals varied in creep strength level, so that one overmatched, one undermatched, and one matched the creep strength of the P911 grade pipe base material. The long-term objective of this work was to study the influence of weld metal creep strength on the overall creep behavior of the welded joints and their failure mechanism. Uniaxial creep tests at 600°C and stresses ranging from 70 MPa to 150 MPa were performed on the cross-weld samples of all three welds. A total creep testing time of more than 470,000 h was accumulated. The longest running sample achieved a time-to-rupture of more than 45,000 h. Creep testing revealed that the use of undermatching weld metal led to a premature fracture in the weld metal at higher stress levels. Compared with undermatching weld metal, the use of matching and overmatching filler materials increased the time-to-r...
Damage characterization of a P91 steel weldment under uniaxial and multiaxial creep
Materials Science and Engineering: A, 2009
Clarification of creep damage mechanism and establishment of remaining life assessment methods of boiler pipings of P91 steel with weldment are important subjects to maintain reliable operation of thermal power plants. In order to characterize the creep damage of a P91 steel weldment and to discuss creep rupture life prediction methods, uniaxial creep tests on a P91 steel cross weld and internal pressure creep tests on a longitudinal welded tube specimen were conducted. Three-dimensional finite-element creep analysis of the longitudinal welded tube specimen was conducted to identify stress and creep strain distribution within the specimen. Creep rupture time of the weld joints was reduced significantly from that of the base metal due to Type IV failure. It was found from an examination of creep damage in interrupted cross weld specimens that creep voids have already initiated around 20% creep damage, and that the number of voids inside the specimens was larger than those at the surface of the specimens. Creep analysis results indicated that triaxial tensile stress yielded at mid-thickness in the heat affected zone (HAZ) of the tube specimen due to differences of creep deformation properties of the base metal, the HAZ and the weld metal. It was suggested that triaxial stress states caused acceleration of creep damage evolution in the HAZ resulting in internal failure of the tube specimens. Rupture life of the longitudinal welded tube specimen under internal pressure creep is predicted from the circumferential steady-state creep strain rate at the HAZ obtained from creep analysis using a three-materials finite-element model of the tube specimen.
The aim of this study is optimizing the creep properties of T91 weld joints at high temperature and pressure. After welding, tube portions were subjected to different cycles of post welding heat treatment, than creep tests at 650°C and a range of pressure values. Crept specimens were exterminated in order to determine the weakest zones in the joint. It was found that the rupture occurs in the base metal at high pressures and in the heat affected zone at low ones. The creep rupture time of weld joint is lower than those of the base metal.Microstructure after creep is compared to the original one, to better understand the impact of creep exposure on microstructure evolution and to evaluate the strength of weld joints.
Experimental Study On Creep Strength Of The Weld Joints Of 9%Cr Heat Resistant Steels
2016
The aim of this study is optimizing the creep properties of T91 weld joints at high temperature and pressure. After welding, tube portions were subjected to different cycles of post welding heat treatment, than creep tests at 650°C and a range of pressure values. Crept specimens were exterminated in order to determine the weakest zones in the joint. It was found that the rupture occurs in the base metal at high pressures and in the heat affected zone at low ones. The creep rupture time of weld joint is lower than those of the base metal.Microstructure after creep is compared to the original one, to better understand the impact of creep exposure on microstructure evolution and to evaluate the strength of weld joints.