Low temperatures, welding

Development of theory and creation of acceptable levels of defects in low-temperature welds. 

Grade LCB low temperature welded carbon steel casting, grade B J03... 

To provide the better inspection of welded joints the parameters of crawlers, working in low temperatures up to - 40°C, and X-ray television introscopes are improved, etc. 

Solidification. The heat of the electric arc melts a portion of the base metal and any added filler metal. The force of the arc produces localized flows within the weld pools, thus providing a stirring effect, which mixes the filler metal and that portion of the melted base metal into a fairly homogeneous weld metal. There is a very rapid transfer of heat away from the weld to the adjacent, low temperature base metal, and solidification begins nearly instantaneously as the welding heat source moves past a given location. 

Impact Testing Materials conforming to ASTM specifications listed in the code may generally be used at temperatures down to the lowest temperature listed for that material in the stress table without additional testing. When welding or other operations are performed on these materi s, additional low-temperature toughness tests may be reqiiired. The code requirements are listed in Table 10-57. 

Low-temperature service is defined as being below—29°C (—20°F), and impact testing of many materials is required. The code is restrictive in the type or welding permitted. 

Nickel Steel Low-carbon 9 percent nickel steel is a ferritic alloy developed for use in cryogenic equipment operating as low as —I95°C (—320°F). ASTM specifications A 300 and A 353 cover low-carbon 9 percent nickel steel (A 300 is the basic specification for low-temperature ferritic steels). Refinements in welding and (ASME code-approved) ehmination of postweld thermal treatments make 9 percent steel competitive with many low-cost materials used at low temperatures. 

Aluminum Aluminum alloys have unusual ability to maintain strength and shock resistance at temperatures as low as —250°C (—425°F). Good corrosion resistance and relatively low cost make these alloys very popular for low-temperature equipment. For most welded construction the 5000-series aluminum alloys are widely used. These are the aluminum-magnesium and aluminum-magnesium-manganese materials. 

The material of constmction of the vessels D and C was not suited for use under low temperature conditions. Vessels A and B were, however, suitable. The location of initial brittle fracture in vessel C was the weld seam near the manhole. Vessel D probably failed as a result of impact from a fragment from vessel C. 

The selection of materials for high-temperature applications is discussed by Day (1979). At low temperatures, less than 10°C, metals that are normally ductile can fail in a brittle manner. Serious disasters have occurred through the failure of welded carbon steel vessels at low temperatures. The phenomenon of brittle failure is associated with the crystalline structure of metals. Metals with a body-centred-cubic (bcc) lattice are more liable to brittle failure than those with a face-centred-cubic (fee) or hexagonal lattice. For low-temperature equipment, such as cryogenic plant and liquefied-gas storages, austenitic stainless steel (fee) or aluminium alloys (hex) should be specified see Wigley (1978). 

WELLS, A. A. (1968) British Welding Journal 15, 221. Fracture control of thick steels for pressure vessels. WlGLEY, D. A. (1978) Materials for Low Temperatures, Engineering Design Guide No. 28 (Oxford U.P.). 

A 333 Seamless and Welded Steel Pipe for Low-Temperature Service [Notes (2) and (4)]... 

A 334 Seamless and Welded Carbon and Alloy-Steel Tubes for Low-Temperature Service... 

Materials With Limited Service. The desirability of specifying some degree of production impact testing, in addition to the weld procedure qualification tests, when using materials with limited low-temperature service experience below the minimum temperature stated in Table IX-2. 

Flexible PVC is appreciated for the versatility of its characteristics according to the formulation. Significant quantities of fillers and plasticizers are used to optimize some of the characteristics such as behaviour at low temperatures, fire resistance, flexibility and hardness in the elastomer range, low price, electric insulation, easy welding and joining, possibility of transparency, food contact, fireproofing. 

Flexible PVC characteristics depend broadly on the formulations flexibility improved low-temperature behaviour fire-retardant grades low cost possible food contact and transparency easy to weld and stick. 

---