Welding stresses elimination

In alloyed air-hardened steels (13 CrMo44), thorough tempering at 750°C is needed after welding to eliminate the hardness structure. Only when the hardness is below 220V are these steels resistant to stress corrosion cracking. 

Ultrasonic (processes) Process which utilizes specially designed tooling usually vibrating at 15-80 KHz. Processes are designed to cause localized heating of thermoplastic materials which, in turn, will provide some type of welded or fused joint. Benefits are elimination of fillers and minimized heat stress on surrounding materials. 

Residual stresses occur from welding and other fabrication techniques even at very low stress values. Unfortunately, stress relief of equipment is not usually a reliable or practical solution. Careful design of equipment can eliminate crevices or splash zones in which chlorides can concentrate. The use of high-nickel stainless steel alloy 825 (40% nickel, 21% chromium, 3% molybdenum and 2% copper) or the ferritic/austenitic steels would solve this problem. 

Today, boilers are welded and stress-relieved, thus ostensibly eliminating a primary component of the SCC process however, modem boilers operate at higher heat fluxes, which imposes a strict requirement for cleaner metal surfaces. The presence of deposits on any waterside surface may provide an opportunity for the concentration of free alkali under the deposit, and so caustic embrittlement still occurs today, depending on inherent stress levels and the particular water chemistry involved. 

This form of corrosion can be prevented in some instances by eliminating high stresses. Stresses developed during fabrication, particularly during welding, are frequently the main source of trouble. Of course, temperature and concentration are also important factors in this type of attack. 

Eliminate notches in design or minimize notch effect as much as possible carefully inspect welds and base material eliminate or minimize vibrations, stress levels. 

Threads are used to transport material from the shoulder down to the bottom of the pin for example, a clockwise tool rotation requires left-handed threads. A round or domed end to the pin tool reduces the tool wear upon plunging and improves the quahty of the weld root directly underneath the bottom of the pin. The best dome radius was specified as 75% of the pin diameter. It was claimed that as the dome radius decreased (up to a flat-bottom tool), a higher probability of poor-quality weld was encountered, especially directly below the pin (Ref 85). The versatility of the cylindrical pin design is that the pin length and diameter can readily be altered to suit the user s needs. Also, machining a radius at the bottom of the threads will increase tool life by eliminating stress concentrations at the root of the threads. 

A typical rack employed for installation of specimens in pilot plants is shown in Fig. 6. Both corrosion coupons, 2 X 1 X 0.35 in. thick, and bend specimens intended to determine stress-corrosion cracking susceptibility, are included in the installation for aqueous corrosion testing. Specimens are separated by high density alumina spacers to eliminate electrochemical effects. During exposure, the racks are welded to existing components in the pilot plant equipment. 

Austenitic or duplex stanless steels undergo a solution annealing and water quenching heat-treatment. Additionnal heat-treatments such as for stress relief or post weld treatment are also used to eliminate the internal stresses of the material. 

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