Stress relief

Stress relief consists of heating the castings at a rate of 50 - 100 °C/h to 600 °C (taking care not to exceed 610 °C), followed by soaking them for a minimum of one hour, plus an extra hour for every 25 mm of section thickness in the thickest section, and then cooling them at a rate of 50 - 100 °C/h or less. The castings must be adequately supported in the furnace so that they are not subjected to stress. 

---

See ASTM A263, A264, A265, and B432. To convert MPa to psi, multiply by 145. Stress relief annealed at 621 °C. 

Residual. Stress-relief-anneal components and assemblies following cold working or welding operations. Note, however, that annealing has no effect on applied stresses. 

Stress-relief-annealing cannot be expected to eliminate SCC in every case. Only residual stresses are reduced in stress-relief-annealing. Applied stresses, which may be responsible for the cracking, will remain. Inhibitors are not 100% effective in combating SCC. Complete coverage and inhibition is difficult to achieve, especially below deposits, in crevices, and in pits. 

Residual stresses caused by large temperature differences between the weld bead and adjacent metal can be reduced by preheating the metals to be welded, especially if the sections are thick, or by stress-relief-annealing following the welding procedure. Proper welding techniques, especially the use of appropriate weld filler metals to minimize weld-metal shrinkage, can minimize residual stresses. 

When stress-relief-annealing 300 series stainless steel components, care must be taken to avoid slow cooling through the sensitization range (see Weld Decay in this chapter). 

By introducing branch points into the polymer chains, for example by incorporating about 2% of 1,2,3,-trichloropropane into the polymerisation recipe, chain extension may proceed in more than two directions and this leads to the formation of networks by chemical cross-links. However, with these structures interchange reactions occur at elevated temperatures and these cause stress relief of stressed parts and in turn a high compression set. 

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. 

Acrylonitrile-butadiene-styrene polymers are similar in stmeture, but the acrylonitrile hardens the polymer. Minute rubber particles act as stress-relief centers, making it good for large objects luggage or car body parts. It can be chrome plated, foamed, injection molded, blown, and alloyed wiih other pla.siic. . 

Spannungs-freiglUhen, n. Metal.) stress-relief anneal, -grad, m. degree of tension, spannungslos, a. without tension or strain Elec.) dead. 

Lack of stress relief Poor material workmanship Inadequate Residence Time to Separate Gas, Lean Oil, Water... 

Stress relief is of little practical value as a means of preventing stress-corrosion cracking in austenitic steels, as cracking occurs at quite low stress levels even in fully softened material and it is difflcult to ensure that stresses are reduced to a safe level in a real structure. The technique can however be useful in small items but, even in this case, phase changes which reduce stress-corrosion resistance or have other deleterious effects can occur at the stress relieving temperature. 

For carbon steels, however, a full stress-relief heat treatment (580-620°C) has proved effective against stress-corrosion cracking by nitrates, caustic solutions, anhydrous ammonia, cyanides and carbonate solutions containing arsenite. For nitrates, even a low-temperature anneal at 350°C is effective, while for carbonate solution containing arsenite the stress-relief conditions have to be closely controlled for it to be effective . 

However, with large vessels, there are two areas where it is difficult to ensure adequate stress relief ... 

In addition, a surprisingly large number of stress-corrosion cracking failures have resulted from the welding of small attachments to vessels and piping after stress-relief heat treatment has been carried out. 

The evidence to date suggests that thermal stress relief prevents cracking in all three environments. 

Silver is often preferred as an undercoat for rhodium by reason of its high electrical conductivity. A further advantage of silver in the case of the thicker rhodium deposits (0-0025 mm) applied to electrical contacts for wear resistance is that the use of a relatively soft undercoat permits some stress relief of the rhodium deposit by plastic deformation of the under-layer, and hence reduces the tendency to cracking , with a corresponding improvement in protective value. Nickel, on the other hand, may be employed to provide a measure of mechanical support, and hence enhanced wear resistance, for a thin rhodium deposit. A nickel undercoating is so used on copper printed connectors, where the thickness of rhodium that may be applied from conventional electrolytes is limited by the tendency of the plating solution to attack the copper/laminate adhesive, and by the lifting effect of internal stress in the rhodium deposit. 

Heat treatment may also affect the extent and distribution of internal stresses. These may be eliminated by appropriate annealing treatments which can remove susceptibility to stress-corrosion cracking. This must be explored in any studies of the performance of materials in environments where stress-corrosion cracking is a hazard. In particular cases, stress-relief annealing treatments may result in the appearance of new phases which, while eliminating the stress-corrosion effects, will induce another type of path of attack. This possibility must be kept in mind in assessing the overall benefits of heat treatments applied primarily for stress relief. 

WIND LOAD DESIGN RADIOGRAPHY % STRESS RELIEF 23... 

---