Lowest service temperature

Ductility is the plastic response to tensile force. Plastic response, or plasticity, is particularly important when a material is to be formed by causing the material to flow during the manufacture of a component. It also becomes important in components that are subject to tension and compression, at every temperature between the lowest service temperature and the highest service temperature. Ductility is essential for steels used in construction of reactor pressure vessels. Ductility is required because the vessel is subjected to pressure and temperature stresses that must be carefully controlled to preclude brittle fracture. Brittle fracture is discussed in more detail in Module 4, Brittle Fracture. 

On the other hand, in plastics which have a high degree of crystallinity (e.g., polyethylene, polypropylene), the amorphous regions are small, so Tg is only of secondary importance. For them it is the melting temperature which will limit the maximum service temperature. The lowest service temperatures which can be used are normally limited by the brittleness introduced into the material. The behavior of plastics materials at room temperature is related to their respective Tg values. This aspect has been dealt with in Chapter 1. 

To measure how much the binder creeps under constant load at lowest service temperature.The creep stiffness and m-value of the asphalt binder contained in the mbc are used as performance-based specification criteria. 

B. Maximum Pressure Below Lowest Service Temperature... 

The maximum allowable pressure below the lowest service temperature is defined by paragraph NB-2332, Section III of the ASME Code, to be 20% of the preoperational hydrostatic test pressure. This test pressure is 125% of the design pressure (2500 psia), or 3125 psia, and 20% of this value is 625 psia. Therefore, the maximum pressure below the lowest service temperature is 625 psia (actual fluid pressure at the inside surface of the beltline). 

Except for the need to employ peel-stress relief, as discussed later, the process of designing the bonded splices in the PABST fuselage really was as simple as looking up entries for the appropriate skin thickness in Fig. 2. The astute reader will observe that no mention has yet been made of the service temperature. This is because the calculations on which Fig. 2 is based were repeated for the highest and lowest service temperatures, and tor room temperature as well. The design overlap is actually set by the maximum temperature, where the adhesive is softest, as is explained later, and the joint strength by the minimum temperature, where the bond strength is least because the adhesive is more brittle then. The tensile... 

Listed uoumetallic materials 6. No ad(htional requirements. 6. Below the recommended minimum temperatures, the designer shall have test results at or below the lowest expected service temperature which assure that the materials will have adequate toughness and are suitable at the design minimum temperatures. 

Thermal contraction of piping must be allowed for, based on the lowest possible service temperature. 

The design minimum temperature is the lowest component temperature expected in service. This temperature may establish special design requirements and material qualification requirements. See also paras. IP-2.1.7(c) and GR-2.1.2(b). 

The chilling effect of sudden loss of pressure on highly volatile fluids as a factor in (feermining the lowest expected service temperature. 

The second reaction depends on an equilibrium which shifts in the desired direction at low temperature. From a thermody namic standpoint, to obtain high hydrogen contents in the efiluent produced (raw s3mthesis gas), the operating conditions must guarantee the lowest possible service temperatures. In practice, this consideration is incompatible with the paitial oxidation operauon w hich, due to its exothennicity, creates a high reaction temperature (950 to 1250 Q. 

The maximum service temperature will also be affected since the resin modulus will tend to drop at the lowest relaxation temperature. Some modified systems also exhibit a larger reduction in Tg because of modifier hydrolysis, especially during thermal excursions. Therefore, an additional safety margin should be added to the highest service temperature. Since the Tg of a thermoset is a direct function of the cure or postcure temperature, a resin cured at 150 °C may have a long-term maximum useful temperature of only 100 °C. This represents the design service temperature of the stracture, although moisture equilibrium will be reached after several years. 

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