JOINING OF PIPES BY MICROWAVE ENERGY

Abstract

Use of metallic pipes in industries (such as oil, chemical, sugar, paper, process and automotive etc.) always necessitateijoining and rework during their service life. Many joining processes are available for metallic pipe joining; however, getting a sound joint at low cost is still a concern for industries. Many joints need rework and consequently consume more productive time and energy. It has been reported that microwave (MW) energy can be used for joining of bulk metals. Use of microwaves for joining of bulk metals have revealed that the process is capable of producing joints with better mechanical and metallurgical properties than conventional joining processes. Other inherent advantages of MW joining include, eco-friendly processing, reduced processing time and enhanced energy saving. Similar results can be expected while joining of metallic pipes using microwave radiations at 2.45 GHz. Thus, a new technique for joining of metallic pipes has been developed through microwave hybrid heating (MHH) technique. This research work reports joining of mild steel (MS) pipes using nickel powder (40 jim) as an interfacing material in a multimode MW applicator at 2.45 0Hz and 900 W. A ceramic fixture was developed for holding and processing the required joints in MW applicator. The basic principles involved in the MW pipe joining process have been discussed. The experiments were carried out on joining of mild steel pipes using different susceptors such as - SiC, graphite and charcoal powder. MS pipe joining using microwave energy with SiC susceptor at 1.4 kW indicates that the increase in exposure time up to 840 s, causes sintering of nickel powder whereas use of graphite plate, as susceptor does not affect the interface powder and base metal as no sintering of sandwich layer was observed up to 1080 s. In both cases no joining of pipes wc4.ç observed. The successful joining of pipes was observed while using charcoal as susceptor at 900 W in exposure time of 480 s. Characterization of the developed joints was carried out through XRD, SEM, optical microstructure, EDS analysis, microhardness, porosity measurement and tensile strength. XRD study shows the higher intensity peaks of the nickel and iron at the joint zone. Elemental mapping result revealed the presence of nickel rich area apart from iron at the entire joint region. The inner surface of the joint zone indicates the 37.91 % of the nickel whereas; outer surface of the joint indicates 10.2 % respectively. The presence of nickel as a dominating element at bottom surface of pipe was due to wider joint area as observed in SEM analysis. The percentage of nickel and iron varies at the inner region of the joint and at the interface of the joint zone indicates the melting and fusion of the interface material and base metal as observed in EDS analysis. The average micro hardness in the joint zone, at interface and at base was observed to be 572 Hv, 5 19 Hv and 397 Hv, respectively. Less porosity at the outer surface of the joint zone was observed (3 ± I %) compared to inner surface of the joint (7 + 2 %). The joint which was exposed for 420 s shows more leakage, where as joints with expose time 480 s were leakage free. The ultimate tensile strength (UTS) and yield stress (YS) of the joint for exposure time of 480 s was 397.27 MPa and 119.96 MPa compared to the UTS (607.908 MPa) and YS (128.5 MPa) of the base metal. The appreciably good joint efficiency (65.4%) was obtained due to the good fusion of the interface material and the base metal. Reduction in the joint efficiency was attributed to the higher percentage of the porosity and overheating of joint area. The model development and simulation of pipe joining was carried out inside the microwave applicator at a frequency of 2.45 GHz and 900 W power using COMSOL multiphysics software tool. At 480s, the temperature of the joint zone was observed to be 15000C, whereas the temperature at the top and bottom end of the pipes were observed to be 12000C and 9000C respectively. The sufficient temperature was observed at the joint zone which melts the interface material and faying surfaces of the metallic pipe. Simulation results are in good agreement with the experimental resuIts.