Stress relieving

Other Techniques. The FEP resin is bonded to metal surfaces by the appHcation of heat and pressure it can be heat sealed or hot-gas welded. Heating FEP at 260°C and allowing it to cool slowly results in stress relieving, or annealing. The FEP film is used to weld PTFE-coated surfaces. 

Overhaul pump replace casing or repair by welding. Stress-relieve after welding as needed. 

For stress-relieved tempers (T3.51, T3510, T3.511, T451, T4510, T4511, T651, T 510, T6511) stress values for material in the listed temper shall be used. 

In handhng caustic, as-welded steel can be used without developing caustic-embrittlement cracking if the temperature is below 50°C (I20°F). If the temperature is nigher and particularly if the concentration is above about 30 percent, cracking at and adjacent to non-stress-relieved welds frequently occurs. 

Insiilating refractories are used mainly in the heat-treating industiy for furnaces of the periodic type. They are also used extensively in stress-relieving furnaces, chemical-process furnaces, oil stills or heaters, and the combustion chambers of domestic-oil-burner furnaces. They usually have a hfe equal to that of the heavy brick that they replace. They are particularly smtable for constructing experi-... 

In general, the higher the residual or applied metal stress, the more severe the corrosion at a given acidic pH. This explains why many heat exchanger tube ends are often attacked so severely (Fig. 7.1). Tube ends that have been rolled or welded often contain high residual stress. Further, crevices are sometimes present in which acidic species may concentrate (see Chap. 2, Crevice Corrosion ). Screens, rolled sheet metal, and other highly worked metals (not stress relieved) are also prone to attack. 

Contain tensile residual stresses which are usually as large as the yield stress. Weld liable to fatigue even when applied stress cycle is wholly compressive. Reduce residual stresses by stress relieving, hammering or shot peening. 

Z Stress relieving may be required for the restoration or improvement of the weld s strength properties. 

Poor Weldability a. Underbead cracking, high hardness in heat-affected zone. b. Sensitization of nonstabilized austenitic stainless steels. a. Any welded structure. b. Same a. Steel with high carbon equivalents (3), sufficiently high alloy contents. b. Nonstabilized austenitic steels are subject to sensitization. a. High carbon equivalents (3), alloy contents, segregations of carbon and alloys. b. Precipitation of chromium carbides in grain boundaries and depletion of Cr in adjacent areas. a. Use steels with acceptable carbon equivalents (3) preheat and postheat when necessary stress relieve the unit b. Use stabilized austenitic or ELC stainless steels. 

Embrittlement embrittlement and for improperly heat treated steel, both of which give intergranular cracks. (Intercrystalline penetration by molten metals is also considered SCC). Other steels in caustic nitrates and some chloride solutions. Brass in aqueous ammonia and sulfur dioxide. physical environments. bases of small corrosion pits, and cracks form with vicious circle of additional corrosion and further crack propagation until failure occurs. Stresses may be dynamic, static, or residual. stress relieve susceptible materials. Consider the new superaustenitic stainless steels. 

In this same amine service it was found that carbon steel pits much more readily if it has not been stress relieved. 

If, after fabrication, heat treatment is not possible, materials and fabrication methods must have optimum corrosion resistance in their as-fabricated form. Materials that are susceptible to stress corrosion cracking should not be employed in environments conducive to failure. Stress relieving alone does not always provide a reliable solution. 

Stress relieving at 600-700°C for steels decreases operation at temperatures some 20°C lower. Unfortunately, suitable furnaces generally are not available, and local stress relieving of welds, etc., is often not successful because further stresses develop on cooling. 

Stress relieving of fabricated filiating covers, or channels GaskL-ts in contact with oil 111 uas... 

Stressed, such as heat-affected zones near welds, in areas of high acid-gas concentration, or at a hot gas-liquid interface. Therefore, stress-relieving all equipment after manufacturing is necessary to reduce corrosion, and special metallurgy in specific areas such as the still overhead or the reboiler tubes may be required. 

The hot potassium carbonate solutions are extremely corrosive. All carbon steel must be stress-relieved to limit corrosion. A variety of corrosion inhibitors are available to decrease corrosion. 

Amine systems are extremely corrosive due to the acid-gas concentrations and the high temperatures. It is important that all carbon steel expo.sed to the amine be stress-relieved after the completion of welding on the particular piece. A system fabricated from stress-relieved carbon steel for DEA solutions, as recommended, will not suffer excessive corrosion. For MEA systems, corrosion-resistant metals (304 SS) should be used in the following areas ... 

Install Coalescer in the Lean Oil and Sponge Oil Streams Stress relieve carbon steel... 

The corrosion rate of nickel in sodium hydroxide is adversely affected by heat transfer by small amounts of oxidisable alkaline sulphur-containing salts, e.g. Na2SOj, NajS Oj, Na S and, at high temperatures, by alkaline oxidising agents, viz. NaClOj and NajOj. In the former circumstance Alloy 600 is more resistant than nickel, but not in the latter. When Alloy 600 is used for service in caustic alkalis, it should be stress relieved after fabrication to minimise the possibility of stress-corrosion cracking. 

Nickel 200 Caustic alkalis, high concentrations and high temperature IG 1. Stress-relieve after fabrication 2. Use low-carbon nickel (0 02% C max.)... 

Alloy 600 Alloy 800 Water-cooled nuclear reactor circuits Usually IG 1. Control alloy composition and processing 2. Control water chemistry 3. Stress relieve after fabrication... 

Yield stress -(MN/m ) 6 UTS (MN/m ) Modulus of eiasticity (GN/m ) Poisson s Hardness ratio (VPN) Resistance to thermal shock Workability (ductile to brittle trans. temp.)( C) Recrystallisation temperature Stress relieving temperature ... 

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