Welding heat-affected zone

Many instances of intergranular stress corrosion cracking (IGSCC) of stainless steel and nickel-based alloys have occurred in the reactor water systems of BWRs. IGSCC, first observed in the recirculation piping systems (21) and later in reactor vessel internal components, has been observed primarily in the weld heat-affected zone of Type 304 stainless steel. 

Hastelloy C-4 is almost totally immune to selective intergranular corrosion in weld-heat-affected zones with high temperature stabihty in the 650-I040 C (I200-I900 F) range Hastelloy C-22 has better overall corrosion resistance and versatihty than either C-4 or C-276 (in most environments). 

This method is the simplest of all the methods and is capable of detecting surface flaws such as corrosion, contamination, surface finish and surface discontinuities on joints.47 The discontinuities on joints such as welds, seals, solder connections and adhesive bonds can be detected. General corrosion, qualitative pitting corrosion, stress-corrosion cracking, weld-heat-affected zone attack, erosion corrosion and other type of degradation can be observed by visual examination aided by microscopes with sufficient magnification. Degradation of plastics can also be detected by visual examination. Visual examination is also used in conjunction with other techniques, such as powerful microscopes. 

The materials behavior (austenitic, austeno-ferritic, and ferritic steels - base metal, welds, heat affected zones) in terms of thermal aging and its effect on mechanical properties, embrittlement, sensitiveness to corrosion (in normal and incidental environment), and radiation effect on the potentially exposed structures. 

As far as provisions affecting both the design and the operation are concerned, the most relevant one is the experimental programme for the measurement of neutron embrittlement. This programme should offer a good indication of the state of the material in the areas of interest (base metal, welds, heat-affected zones) well ahead of time the specimens, that is, must be located where the neutron... 

As a result of the above tests, a relationship was established between the carbon content of 304 stainless steel and weld heat input. This relationship is used to avoid weld heat-affected-zone sensitization as described below. 

Weld heat affected zone sensitized austenitic stainless steels (which will fail the Strauss Test, ASTM A 708) are avoided by careful control of ... 

The non-electrochemical techniques include direct immersion of materials samples in the test fluid in either the laboratory or plant. These s lmples sometimes have an artificial crevice generated with a serrated washer. They may be welded to determine the effects of welds and weld heat affected zones. Real-time information can be obtained using electrical resistance probes. Heat transfer effects can be evaluated by having a test sample that is exposed to the corrodent on one side and the other side heated or cooled. Stressed samples are used to evaluate stress corrosion cracking tendencies [33]. 

Flow proceeds from the lower plenum, through the core. The steam and water are separated the steam is then dried and passed to the turbine. Other flow (see above) returns to the recirculation system. Feedwater is introduced to the annulus between the core shroud and reactor vessel (Fig. 4). The recirculation system piping is a primary pressure boundary for the high-pressure, high-temperature reactor coolant. Type 304 stainless steel was selected for recirculation system piping and numerous other auxiliary systems (such as the reactor water cleanup system, residual heat removal system, core spray, and other emergency core cooling systems) for its corrosion resistance and adequate mechanical properties. Failures of weld heat affected zones... 

Low Temperature Sensitisation of Type 304 Stainless Steel Pipe Weld Heat Affected Zone... 

Elbows at Boiling Water Reactors on February 6, 1997 [5.21] which notes that the riser elbow cracking observed at both BWRs occurred in the weld heat-affected zone of the riser elbow to thermal sleeve attachment weld appears to be characteristic of IGSCC. 

Although there is potential for IGSCC at weld heat-affected zones exists in some BWRs where the LPCI coupling was fabricated from Type 304 stainless steel, no incidents of cracking have been observed. 

IGSCC of the core spray internal piping has been found in a number of BWR plants with relatively high lifetime average water conductivity. Currently, core spray internal piping is visually inspected to the provisions of NRC Bulletin 80-13 [6.3]. However, such visual inspection does not provide information concerning the creviced locations and the inside diameter of weld heat-affected zone. 

The composition of type 439L will be foimd in Table 7.5. This alloy is nonhardenable through heat treatment and has excellent ductility and weldability. It resists intergranular attack and formation of martensite in the as-welded, heat-affected zone, but is subject to 885°F (475°C) embrittlement. 

Alloy B-2 has improved resistance to knifeline and heat-affected zone attack. It also resists formation of grain-boimdary precipitates in weld-heat-affected zone. 

Alloy C-22 resists the formation of grain boundary precipitates in the weld-heat-affected zone. Consequently, it is suitable for most chemical process applications in the as-welded condition. 

HASTELLOY alloy B-2—An improved wrought version of HASTELLOY alloy B. Alloy B-2 has the same excellent corrosion resistance as alloy B, but with improved resistance to knife-line and heat-affected zone attack This alloy resists the formation of grain-boundary carbide precipitates in the weld heat-affected zone, thus making it suitable for most chemical process applications in the as-welded condition. Alloy B-2 also has excellent resistance to pitting and stress-corrosion cracking it is particularly well suited for equipment handling hydrogen chloride gas. and hydrochloric, sulfuric, acetic, and phosphoric acids. 

It consists of heating to a temperature below the lower critical temperature line A1 for the purpose of reducing the fabrication and welding stress and softening the weld heat-affected zones. 

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