Characterization of Microstructure of HAZs in As-Welded and Service Condition of P91 Pipe Weldments

C. Pandey,A. Giri,M. M. Mahapatra,P. Kumar 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.1

Steels 9-12% Cr, having the high creep rupture strength are advocated for the modern low polluting thermal power plants. In the present investigation, the P91 pipe weldments have been characterized for microstructural responses in as-welded, post-weld heat treatment (PWHT) and ageing conditions. The PWHT of welded samples were carried out at 760 °C for time of 2 h and ageing at 760 °C for 720 h and 1440 h, respectively. The effect of time has been studied on precipitates size, distribution of precipitates and grain sizes present in various zones of P91 steel weldments. The impact toughness and hardness variation of heat affected zone (HAZ) have also been studied in as-welded condition as well as at different heat treatment condition. A significant change was observed in grain size and precipitates size after each heat treatment condition. The maximum impact toughness of HAZ was obtained after PWHT at 760 °C for 2 h. The main phase observed in weld fusion zone in as-welded, PWHT and ageing conditions were M23C6, MX, M7C3, Fe-rich M3C and M2C. The unwanted Z-phase (NbCrN) was also noticed in weld fusion zone after ageing of 1440 h.

Study on Suitable Semen Additives Incorporation into the Extender Stored at Refrigerated Temperature

Bhakat, M.,Mohanty, T.K.,Raina, V.S.,Gupta, A.K.,Pankaj, P.K.,Mahapatra, R.K.,Sarkar, M. Asian Australasian Association of Animal Productio 2011 Animal Bioscience Vol.24 No.10

The objective of this study was to compare the effect of Butylated Hydroxy Toluene (BHT), Pentoxifylline (PTX) and ${\alpha}$-tocopherol (Vit E) on semen quality parameters of Karan Fries bulls. The fortification of extender by various semen additives improves motility as well as fertility of spermatozoa. Split samples of 24 ejaculates of four Karan Fries bulls were extended in extender with or without various additives such as BHT, PTX and Vit E, and performance was evaluated at an interval of 0, 24, 48 and 72 h at refrigerated temperature (4-$7^{\circ}C$). Results of the present study revealed that addition of BHT, PTX and Vit E in extender improved sperm cell function, such as motility, viability, HOST, and acrosome integrity, as compared to the control during liquid storage up to 48 h of preservation at refrigerated temperature. There was no significant (p<0.05) difference between any of the additives up to 48 h of preservation. Overall, the results showed a significant (p<0.05) deterioration in motility after each storage interval. The results showed a significant deterioration in the acrosome integrity and plasma membrane integrity up to 48 h; subsequently, there was not much degradation of both the semen quality parameters. There was a significant increase in spermatozoal tail and total abnormality after each storage interval at refrigerator temperature (4 to $7^{\circ}C$); however, the head and mid-piece abnormalities were almost unaffected. Tail and total abnormality were least in extender fortified with BHT, PTX and Vit E at different hours of incubation as compared to the control. The addition of 1.5 mM BHT, 3.6 mM PTX and 1 mg/ml Vit E in the semen extender has more beneficial effect in terms of semen quality and preservability of spermatozoa.

Soluble conducting polymer-functionalized graphene oxide for air-operable actuator fabrication

Ramasamy, M.,Mahapatra, S.,Yoo, H.,Kim, Y.,Cho, J. Royal Society of Chemistry 2014 Journal of Materials Chemistry A Vol.2 No.13

An effective route for the preparation of a processable, conducting polymer-functionalized graphene oxide for actuator applications is investigated. First, graphene oxide (GO) is covalently functionalized with a 3-thiophene acetic acid (TAA) monomer by an esterification reaction. Then, the TAA-functionalized GO is self-polymerized by chemical oxidative polymerization to yield poly(3-thiophene acetic acid)functionalized GO (GO-f-PTAA). Further, the GO-f-TAA is also copolymerized with thiophene (Th) to yield GO-f-PTAA-co-PTh. The synthesis of GO-f-PTAA and GO-f-PTAA-co-PTh composites is confirmed by Fourier transform infrared, H-1-nuclear magnetic resonance, and X-ray photoelectron spectroscopies. The composites show better electrochemical properties than pure PTAA and superior solubility in organic solvents compared to pure GO. Using the soluble GO-f-PTAA and GO-f-PTAA-co-PTh composites, air-operable actuators are fabricated and their actuation performance is investigated. The copolymer-functionalized GO actuator exhibits good electroactive actuation behavior between 2 and 4 V, mainly because of the enhanced electrochemical performance of the composites, whereas the pure PTAA and GO-f-PTAA actuators do not show actuation under the applied voltage. The soluble conducting polymer-functionalized graphene composites developed in this study have potential applications in the fabrication of actuators that can be operated in air.

MODELING HETEROSTRUCTURES WITH SCHRÖDINGER–POISSON–NAVIER ITERATIVE SCHEMES, EFFECT OF CARRIER CHARGE, AND INFLUENCE OF ELECTROMECHANICAL COUPLING

D. ROY MAHAPATRA,M. WILLATZEN,R. V. N. MELNIK,B. LASSEN 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2012 NANO Vol.7 No.4

This paper presents a detailed investigation of the e®ects of piezoelectricity, spontaneous polarization and charge density on the electronic states and the quasi-Fermi level energy in wurtzite-type semiconductor heterojunctions. This has required a full solution to the coupled Schr€odinger?Poisson?Navier model, as a generalization of earlier work on the Schr€odinger ?Poisson problem. Finite-element-based simulations have been performed on a AlN/GaN quantum well by using both one-step calculation as well as the self-consistent iterative scheme. Results have been provided for ¯eld distributions corresponding to cases with zero-displacement boundary conditions and also stress-free boundary conditions. It has been further demonstrated by using four case study examples that a complete self-consistent coupling of electromechanical ¯elds is essential to accurately capture the electromechanical ¯elds and electronic wavefunctions. We have demonstrated that electronic energies can change up to approximately 0.5 eV when comparing partial and complete coupling of electromechanical ¯elds. Similarly, wavefunctions are signi¯cantly altered when following a self-consistent procedure as opposed to the partial-coupling case usually considered in literature. Hence, a complete self-consistent procedure is necessary when addressing problems requiring more accurate results on optoelectronic properties of lowdimensional nanostructures compared to those obtainable with conventional methodologies.

Microstructure Characterization and Charpy Toughness of P91 Weldment for As-Welded, Post-Weld Heat Treatment and Normalizing & Tempering Heat Treatment

Chandan Pandey,M. M. Mahapatra,Pradeep Kumar,A. Giri 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.5

The effect of weld groove design and heat treatment on microstructure evolution and Charpy toughness of P91pipe weldments was studied. The P91 pipe weldments were subjected to subcritical post weld heat treatment(760 °C-2 h) and normalizing/tempering conditions (normalized-1040 °C/40 min, air cooled; tempered 760 °C/2 h,air cooled) were employed. The influence of subsequent PWHT and N&T treatment on the microstructure of variouszone of P91 pipe weldments were also investigated. The present investigation also described the effect ofPWHT and N&T treatment on hardness, grain size, precipitate size, inter-particle spacing and fraction area of precipitatespresent in each zone of P91 pipe weldments. The result indicated great impact of heat treatment on theCharpy toughness and microstructure evolution of P91 weldments. The N&T treatment was found to be moreeffective heat treatment compared to subsequent PWHT. Charpy toughness value was found to be higher for narrow-groove design as compared to conventional V-groove design.

A Study on the Effect of Weld Groove Designs on Residual Stresses in SS 304LN Thick Multipass Pipe Welds

A. Giri,M. M. Mahapatra,K. Sharma,P. K. Singh 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.1

Present research describes the effect of weld groove designs on residual stresses of thick SS 304LN pipe welds which are commonly utilized for applications such as boiling water reactor system, oil and steam piping. The faying surfaces of the pipe joints were machined to generate conventional and narrow groove geometries for welding. Circumferential multipass pipe welding was carried out without applying preheat and post weld heat treatment. Blind hole drilling technique was employed for measuring hoop and axial residual stresses in narrow and conventional grooved SS 304LN pipe welds considering plasticity and stress concentration effects of hole drilling process. The result exhibited 20 to 30 percent reduction in residual stresses in narrow grooved pipe welds. A finite element model was developed for estimating the pass by pass peak temperature distributions in the pipe welds. Sequentially coupled thermomechanical elastic-plastic analysis of both conventional and narrow groove pipe welds indicated close agreement between the predicted and experimentally determined hoop and axial residual stresses.

Influence of heat treatment conditions of Al-Cu aluminum alloy on mechanical properties of the friction stir welded joints

Muralimohan Cheepu,D. Venkateswarlu,M. M. Mahapatra,Woo-Seong Che 대한용접·접합학회 2017 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2017 No.11

On the Prediction of Effect of Direction of Welding on Bead Geometry and Residual Deformation of Double-sided Fillet Welds

C. Pandey,A. Giri,M. M. Mahapatra 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.2

The present study describes how the effect of direction of welding is useful to minimize distortion in submerged arc welded double-sided fillet joints. In present work, angular distortion of 12 mm thick double-sided fillet welds was measured for same direction and reverse direction welding. It has been observed that the maximum magnitude of the angular distortion for reverse direction fillet welding is lower. Thermal history in horizontal and vertical plate of fillet welds was also measured for both same direction and reverse direction welding. After welding, the fillet welds were sectioned, polished and etched to measure the effect of direction of welding on weld bead geometry. To predict the temperature distribution and thermal history, a finite element (FE) elasto-plastic thermo-mechanical model has been developed for submerged arc welded double-sided fillet welds by using moving distributed heat source. The three-dimensional FE thermal model was verified by comparing peak temperature obtained with experimental values. The model results matched fairly well with experimental results with a variation of 6 percent for sample 1 and 7.5 percent for sample 2 for the maximum values of distortion, and a variation of 2-8 percent for peak temperatures in horizontal plate and 9 percent in web plate.

On the Estimation and Control of Welding Distortion of Guide Blade Carrier for a 660 MW Turbine by Using Inherent Strain Method

A. Vishvesha, C. Pandey,M. M. Mahapatra,R. S. Mulik 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.1

While predicting the welding distortion for a complex welded structure like the guide blade carrier assembly of power generation turbine, the traditional thermo-mechanical models commonly utilized for geometrically simple welded butt and T joints may not be adequate. For large and complex welded structures,the thermo-mechanical elasto-plastic analysis can be computationally prohibitive. Other than simplistic butt and T joints, the aforementioned distortion prediction technique is not so suitable to provide reliable results when applied to large complex 3-D welded structures. Hence, inherent strain method is proposed here to predict distortion in an outer ringof GBC (Guide Blade Carrier) of a steam turbine. Such welded outer rings of GBC are large welded structures having many welded joints of different weld geometries at several planes. In the present study, inherent strain based technique was utilized for the aforementioned welded structure in elastic finite element analysis for the accurate prediction of 3-D distortion patterns with reduced computational time. The predicted and measured values of 3- D distortions of GBC were observed to be in good agreement with the ones provided from the shop floor, indicating the adequacy of inherent strain based method for the prediction of welding distortion in large and complex welded structures. As part of this investigation, a suitable welding fixture was also designed and welding sequence was modified, which were verified through inherent stain method to aid in minimizing the distortion of welded GBC.

Experimental and Numerical Study on Effect of Weld Reinforcement on Angular Distortion of SAW Square Butt Welded Plates

H. K. Narang,M. M. Mahapatra,P. K. Jha,PVSS Sridhar,P. Biswas 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.2

Weld reinforcements play vital role in controlling different formation of inherent strains in the heat-affected zone in arc welded joints. It is desirable to have adequate weld reinforcements on both the top and bottom sides of butt joint such that shrinkage force effects of both the reinforcements would be cancelling the angular distortion. In this study, it has been established by experiments that acceptable top and bottom weld reinforcements can be achieved and angular distortion can be controlled in square butt joints through submerged arc welding (SAW) done from both the sides with accurate control of welding process parameters. Such process does not require use of costly backing strip and instead a flux bed can be used for the purpose. Modeling of the process was also carried out using 3-D thermomechanical finite element (FE) analysis. Moving distributed heat source, weld reinforcements on top and bottom side, weld deposition in each welding pass and temperature dependent thermos-physical properties were used in the thermomechanical analysis for predicting the temperature profiles and angular distortion patterns The numerically predicted temperature distribution and distortion patterns indicated close agreement with the experimentally observed results.