|Content Type||Conference Paper|
|Title||Flux-Core Welding in Refinery Service|
|Authors||Richard L Colwell, Bechtel Corporation; William Layo, Midalloy|
|Source||CORROSION 2008, March 16 - 20, 2008 , New Orleans LA|
|Copyright||2008. NACE International|
|Keywords||Flux-Core Arc Welding(FCAW), semi-automated, consumables, refinery, wire, shielding gas, enviromental cracking, wet H2S, pressure vessel, hear exchanger, piping , fabrication|
While its reputation has been stigmatized by early quality problems in the 1980?s, Flux-Core Arc Welding (FCAW) has evolved into a process by which experienced fabricators can obtain radiographic quality welds in many alloy systems. Research and development, modern manufacturing techniques, and improvement in sensor and inspection technologies have produced consumables for gas-shielded procedures that can meet many petroleum refinery industry specifications. During the last decade there has been increased pressure exerted by fabricators on buyers to utilize Flux-Core Arc Welding (FCAW) where possible, today?s competitive market has enabled fabricators to persuade segments of the power, chemical, and petroleum processing industry to accept FCAW for pressure vessel, heat exchanger, and piping fabrication applications in order to reduce both cost and schedule. Even though many refinery owner/operators? specifications prohibit the use of the FCAW for radiograph quality welds, there has been a growing trend to rethink the restriction, and allow the controlled use of FCAW (gas shielded) for petroleum refinery pressure retaining welds. This paper discusses the author?s experiences with the increasing use and ongoing limitation of FCAW(G).
Flux-Core Arc Welding (FCAW) is a variation of the Gas Metal Arc Welding (GMAW) process, and is generically considered a "semi-automatic" process. Like GMAW welding, consuming wire is fed into the molten weld pool at a controlled rate. Flux-Core arc welding can be further characterized as self-shielding FCAW(S) or gas shielded FCAW(G). FCAW(S) is commonly chosen in structural steel fabrication due to its advantage of providing high deposition rates. For the purpose of this discussion, as it relates to pressure boundary weldments of radiographic quality, only the gas shielded process, FCAW(G), will be discussed in any detail. Flux cored welding produces a protective slag covering that is easily removed when correct welding parameters are followed. Flux cored welding has good bead appearance (smooth, uniform welds having good contour). It has been reported that 1957 saw the debut of the flux-cored arc welding process. This new process promoted the use of self-shielded coiled wire electrode that could be used with existing semi-automatic equipment, increasing the efficiency of welding fabrication projects. In FCAW(S) the electrode wire Is fed continuously to the work piece. This increases arc time and avoids stub losses typical of the shielded metal arc welding (SMAW) process. Another new wire, called an inside-outside electrode, had a tubular cross section with the fluxing agents in the annulus was also introduced at this time. The process was called Dualshield ®1, was characterized by two modes of shielding gas; external gas and shielding gas created by the thermal breakdown of the annular fluxing agents. This process, invented by Bernard, was patented in 1957. Since that time the patent was acquired by a succession of companies, and is now owned by ESAB1. One thing to note is that these original dual shield wires were native to the USA, and for nearly 40 years no foreign source could compare/ compete. Since then many other major supplier of FCAW(G) filler wires have entered the market.
|File Size||4346 KB||16|