Strength thermal limits

Epoxy Mortars Epoxies are the strongest resin mortars, have the best bond strength to other CRM materials, and resist many solvents, mild to moderate acids, non-oxidizing and alkaline media. Their useful pH range is about 2-14, and their thermal limit is approximately 230°F. Besides their excellent alkali and dilute acid resistance, epoxy mortars handle many organic chemicals and sodium hypochlorite at low temperatures. Epoxies should not be exposed to acetic acid and its esters. Epoxy mortars have the best physical and mechanical properties of all the resin mortars. 

A base polymer, such as an ethylene-propylene (EP) copolymer, can be acquired in a range of compositions, molecular weights, various ethylene-to-propylene ratios, various molecular weight distributions, and a range of densities. Each of these variations results in a base polymer that has specific practical properties such as flexibility, elastic recovery, tensile strength and thermal limit to name a few. As a base polymer, ethylene-propylene polymers and most other non-crosslinked elastomers have no significant commercial application, since they are essentially a liquid with veiy high viscosity. 

Composihoti, wt% Strength, MPa Modulus thermal limits, °C expansion... 

Silicone adhesives have very good thermal stability, but low strength. Their primary application is in non-structural uses, such as high-temperature pressure-sensitive tapes. Attempts have been made to incorporate silicones in other adhesives, such as epoxies and phenolics, but long cure times and low strength have limited their use. The maximum service temperature for silicone adhesive/sealants is 260°C for continuous operation and up to 316°C for intermittent exposure, depending on the type used. 

A number of other specialized adhesion testing methods have been tried, but most apply only to a very limited class of materials. These other methods use many other techniques, such as surface indentation probes or acoustic or thermal shock of the coating to get an idea of the film adhesion. In addition to being applicable only to a small class of materials, all of these techniques are plagued by the lack of a direct relation to adhesive strength and limited use and experience with the technique. Reference 16 reviews a few of the more common methods of adhesion testing. 

Computed stresses are based on test thickness at test temperature. Since water pressure is a short-term condition, the allowable stresses for structural parts such as supports are frequently increased by a factor of 1.2. The upper limit of stress in the vessel shell during a hydrotest of pressure parts is not specified by the Code. However, it is a good engineering practice to limit the maximum membrane stress in any part of the vessel during a hydrotest to 80 percent of the yield strength. Thermal expansion stresses and local mechanical stresses will be absent and need not be considered. 

Although thermal performance is a principal property of thermal insulation (13—15), suitabiHty for temperature and environmental conditions compressive, flexure, shear, and tensile strengths resistance to moisture absorption dimensional stabiHty shock and vibration resistance chemical, environmental, and erosion resistance space limitations fire resistance health effects availabiHty and ease of appHcation and economics are also considerations. 

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