Stainless steels welding procedure

The duplex range of stainless steels can be readily cast, wrought and machined. Problems can occur in welding, due to the need to keep the correct balance of ferrite and austenite in the weld area, but this can be overcome using the correct welding materials and procedures. 

In submerged arc-welding, the strip electrode is fed from a coil into the flux bed and fused in the arc. The width of the weld deposit corresponds approximately to the width of the electrode, and mixing with the substrate depends on the process parameters. The procedure is preferably used to clad stainless steels. Because of bum-off and mixing, the electrode must be overalloyed to compensate for the loss of important elements. 

Extensive testing on stainless steel mockups, fabricated using production techniques, has been conducted to determine the effect of various welding procedures on the susceptibility of unstabilized 300 series stainless steels to sensitization-induced intergranular corrosion. Only those procedures and/or practices demonstrated not to produce a sensitized structure are used in the fabrication of RCPB components. The ASTM standard A 708 (Strauss Test) is the criterion used to determine susceptibility to intergranular corrosion. This test has shown excellent correlation with a form of localized corrosion peculiar to sensitized stainless steels. As such, ASTM A 708 is utilized as a go/no-go standard for acceptability. 

TAPPI TIP 0402-29, Qualification of Welding Procedures for Duplex Stainless Steels, TAPPI, Atlanta, GA, 2001. 

A microstructured monolith for autothermal reforming of isooctane was fabricated by Kolb et cd. from stainless steel metal foils, which were sealed to a monohthic stack of plates by laser welding [73]. A rhodium catalyst developed for this specific application was coated by a sol-gel technique onto the metal foils prior to the sealing procedure. The reactor carried a perforated plate in the inlet section to ensure flow equi-partition. At a weight hourly space velocity of 316 L (h gcat). S/C 3.3 and O/C 0.52 ratios, more than 99% conversion of the fuel was achieved. The temperature profile in the reactor was relatively flat. It decreased from 730 °C at the inlet section to 680 °C at the outlet. This was attributed to the higher wall thickness of the plate monolith compared with conventional metallic monolith technology. The reactor was later incorporated into a breadboard fuel processor (see Section 9.5). 

Corrosion problems on process units often first show up as weld leaks. More precisely, the failures occur in the heat-affected zone adjacent to the weld. The welding procedure lowers corrosion resistance at the metal grain boundaries in the heat-affected zone. Stress relieving and improved welding techniques will not necessarily mitigate the problem. Use of low-carbon steels or Type 321 stainless (contains titanium) and Type 347 stainless (contains columbium) for replacement piping subject to frequent weld leaks will minimize the rate of failure. 

Titaniuin and most titanium alloys can be welded by arc, spot, seam, flash, pressure, friction and electron beam methods. Procedures and equipment are generally similar to those used for welding austenitic stainless steel or aluminum. However, because titaniixm and titanium alloys are extremely reactive above 540 °C (1000 °F), precautions mvist be taken to shield the joint frnm air. No flux is used when welding titaniimi. 

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