Nowadays, repair welding on in-service gas pipeline is a matter or primary concern of KOGAS (Korea Gas Corporation). KOGAS requires a systematical study for repair welding of API 5L Gr. X65 main pipeline that is in service. Therefore, this study was undertaken to investigate the effect of welding conditions on allowable heat input of repair weld onto in-service natural gas pipeline. First of all, single pass weld bead on plates of various thickness was deposited to evaluate the penetration of weld metal, the depth of heat affected zone and the hardness of repair weld under various welding conditions. SMAW (shielded metal arc welding) with E9016-G and GTAW (gas tungsten arc welding) with ER70S-G were applied to weld the plates whose wall thickness remained of 4, 6, 8 and 10 mm. Also, finite element analysis has been conducted to develop an appropriate model for repair welding. This analysis model was validated by means of data obtained on experimental results of bead-on plate welds. The results of the analysis are temperature profile and cooling rate under various welding conditions. From the results of metallographic examination and hardness survey of bead-on-plate welds, the penetration of weld metal and depth of HAZ (heat-affected zone) in SMAW welds was deeper than that of in GTAW welds, at a given heat input. And, the hardness of the welds by GTAW process was higher than that by SMAW at a given heat input. From the results of the bead-on-plate welds conducted to establish the limit parameters to avoid burnthrough and stress corrosion cracking, it appears that it is feasable to carry out repairs with heat input, ranging from 11.0 kJ/cm to 21.8 kJ/cm on 8 mm thick plate, and from 18.0 kJ/cm to 29.5 kJ/cm on 10 mm plate with the SMAW process. The allowable heat input range for the GTAW process is from 22.2 kJ/cm to 41.7 kJ/cm on 8 mm thick plate and from 19.5 kJ/cm to 47.6 kJ/cm on 10 mm thick plate. From the numerical analysis of heat transfer during bead-on-plate welding, it is known that the linear regression of depth of HAZ is reasonable and the variation of HAZ hardness with heat input and the plate thickness can be explained by the cooling time in HAZ.
The effect of welding conditions during pipeline maintanance welding
Die Effekte von Schweißbedingungen während des Repararturschweißens von Erdgaspipelines
2000
9 Seiten, 7 Bilder, 2 Tabellen, 10 Quellen
Conference paper
Storage medium
English
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