Low temperature service

Most refrigeration systems are essentially the same as the heat pump cycle shown in Fig. 6.37. Heat is absorbed at low temperature, servicing the process, and rejected at higher temperature either directly to ambient (cooling water or air cooling) or to heat recovery in the process. Heat transfer takes place essentially over latent heat profiles. Such cycles can be much more complex if more than one refrigeration level is involved. 

Mihtary interest in the development of fuel and thermal resistant elastomers for low temperature service created a need for fluorinated elastomers. In the early 1950s, the M. W. Kellogg Co. in a joint project with the U.S. Army Quartermaster Corps, and 3M in a joint project with the U.S. Air Force, developed two commercial fluorocarbon elastomers. The copolymers of vinyUdene fluoride, CF2=CH2, and chlorotrifluoroethylene, CF2=CFC1, became available from Kellogg in 1955 under the trademark of Kel-F (1-3) (see Fluorine compounds, ORGANic-POLYcm.OROTRiFLUOROETHYLENE Poly(vinylidene) fluoride). In 1956, 3M introduced a polymer based on poly(l,l-dihydroperfluorobutyl acrylate) trademarked 3M Brand Fluorombber 1F4 (4). The poor balance of acid, steam, and heat resistance of the latter elastomer limited its commercial use. 

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. 

Because of the need to operate more efficiently at low teiTmera-tures, the simple heat exchangers have generally been replaced with more sophisticated types. Guidance for the development of such units for low-temperature service include the following factors ... 

Materials selection for low-temperature service is a specialized area. In general, it is necessaiy to select materials and fabrication methods which will provide adequate toughness at all operating conditions. It is frequently necessaiy to specify Charpy V-notch (or other appropriate) qu fication tests to demonstrate adequate toughness of carbon and low-aUoy steels at minimum operating temperatures. 

When the temperamre is lowered, rubbers become stiff and brittle. All rubbers eventually stiffen to a rigid, amorphous glass at the glass transition temperature (Tg). This temperature also indicates the low-temperature service limit of the rubber. Tg values are dependent on the structure, degree of cross-linking (vulcanization) and isomeric composition of the rubber. 

FPN No. 2) Low ambient conditions require special consideration. Explosionproof or dust-ignitionproof equipment may not be suitable for use at temperatures lower than -25°C (-13°F) unless they are approved for low-temperature service. However, at low ambient temperatures, flammable concentrations of vapors may not exist in a location classified Class I, Division 1 at normal ambient temperatures. 

Examples A, O-rings for rotary and static applications (43) B, extruded items such as hose, tube, and solid splicable stock C, fuel hose for low temperature service (—57°C) and coated fabric for collapsible fuel storage tanks (40, 45) D, biomedical applications such as soft denture liners (48) and blood compatible parts E, lip seals (42) F, shock absorption and vibration damping mounts, (Photograph courtesy of the Firestone Tire... 

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. 

Waste-Form Stability. If they occur at all, solid state transformations in dry glass and UO2 matrices will be too slow under the temperature conditions of service to be observable in the laboratory at the same temperature. Here we need to extrapolate from high temperature laboratory conditions to low temperature service conditions. It will be desirable to develop an intimate knowledge of the processes of phase separation and devitrification of sodium borosilicate glasses at temperatures below the softening point by meticulous application of electron microscopic. X-ray crystallographic and other techniques. The glasses will contain inactive elements representative of the fission product... 

To avoid brittle failures, materials of construction for low temperature service shall be suitable for the minimum design metal temperature in accordance with the codes and other requirements specified. The purchaser and the vendor shall agree on any special precautions necessary with regard to conditions that may occur during operation, maintenance, transportation, erection, commissioning and testing. 

ASTM A 352, Standard specification for steel castings, ferritic and martensitic, for pressure-containing parts, suitable for low-temperature service. 

The obvious comment could be that if the O ring was designed for low temperature service the leakage could not have happened. But then, O rings cannot be designed for operational faults such as this. 

Flat-bottomed, vertical, cylindrical storage tanks for low-temperature service , BSi, BS 7777 Part 1. 1993... 

Other opportunities for stress concentration in bonded joints that may be aggravated by low-temperature service include trapped gases or volatiles evolved during bonding, residual stresses in adherends as a result of the release of bonding pressure, and elevated-temperature cure (i.e., shrinkage and thermal expansion differences). 

Significant differences in the thermal expansion coefficient between the substrate and the adhesive can cause severe stress at the interface. This is common when plastics are bonded to metals because of the difference in thermal expansion coefficients between the substrates. Residual stresses are compounded by thermal cycling and low-temperature service. Selection of a resihent adhesive or adjustments in the adhesive s thermal expansion coefficient via fillers or additives can reduce such stress. 

B. D. Craig, T. V. Bruno, W. M. Buehler. Complexities of Failure Analyses in Sour Systems. Canadian Welding Society/American Society for Metals conference Materials and Welding for Sour Service and Low Temperature Service . Calgary, Alberta, Canada, 1997-11-20/21. 

This guide covers the following materials and corrosion allowance (CA) for process equipment materials for low-temperature services and materials for wear and abrasion resistance. EQUIPMENT DESIGN UFE ... 

GENERAL GUIDELINES FOR MATERIALS SELECTION FOR LOW-TEMPERATURE SERVICES... 

PDMS is the mainstay of the silicone industry, and the majority of its applications are related to its unusual surface properties. Most of these applications are not the result of surface behavior alone but come from desirable combinations of surface properties and other characteristics, such as resistance to weathering, high- and low-temperature serviceability, and high gas permeability. These applications are all a direct consequence of four fundamental structural properties of PDMS, namely (1) the low intermolecular forces between the methyl groups, (2) the unique flexibility of the siloxane backbone, (3) the high energy of the siloxane bond, and (4) the partially... 

The grades of steel normally specified for low temperature service and the minimum temperature of mill Charpy V notch acceptance testing, as abstracted from ASTM A-20-81b "Standard Specification For General Requirements For Steel Plates For Pressure Vessels" are as shown in Table 3-2. 

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