Service condition

Service conditions can adversely affect the performance of a part. The conditions could be the composition of the environment in which the component is used, its temperature, and pressure. If the composition of the environment is such that the environment corrodes the material, then the performance of the component is adversely affected. Higher temperatures generally decrease the strength of a material. Increasing the pressure of the environment may not decrease the life of a component as long the material is ceramic. This is because ceramics possess good compressive strength. 

Ageing is defined as a general process in which characteristics of components, systems and structures gradually change with time or use. This process eventually leads to degradation of materials subjected to normal service conditions These include normal operation and transient conditions under which the component, system or structure is required to operate. Postulated accident and post-accident conditions are excluded [2] and should be evaluated on a case-by-case basis for the effect on the reactor safety and utilization. 

In a research reactor facility, the effects of such degradation may result in the reduction or the loss of the ability of components, systems and structures to function within accepted criteria. Safety and utilization of the facility may be affected unless preventive measures have been taken, and corrective measures have been established. 

Service conditions which contribute to ageing act through chemical and physical processes that affect material properties or functional capabilities. These are  

Environmental factors such as radiation, high humidity or the presence of chemically active liquids or gases (before or during operation)  

Service wear and corrosion, including changes in the dimensions and/or the relative position of individual parts of assemblies  

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Knockout vessels are the most common form of basic separator. The vessel contains no internals and demisting efficiency is poor. However, they perform well in dirty service conditions (i.e. where sand, water and corrosive products are carried in the well stream). 

During a hydrotest the additional weight of the water superimposes the normal operational stress by steam pressure. The big advantage of the pneumatic test is now, that it is the best imitation of the normal service condition. 

Non-Desfructive testing can be apph ed widely in all industrial organisations during construction and after construction to determine, in first case, whether flaws have been introduced due to manufacturing process or in the second case, whether flaws have developed dtie to service conditions. NDT is therefore used to inspect... 

Hardness. Glass hardness tests usually measure the resistance to abrasion by grinding or grit-blasting, resistance to scratching, or penetration by an indenter. The method to be used depends on expected service conditions. Knoop hardness (Table 4) is commonly used, because other methods usually fracture the glass. 

Fatigue. Engineering components often experience repeated cycles of load or deflection during their service fives. Under repetitive loading most metallic materials fracture at stresses well below their ultimate tensile strengths, by a process known as fatigue. The actual lifetime of the part depends on service conditions, eg, magnitude of stress or strain, temperature, environment, surface condition of the part, as well as on the microstmcture. 

Plasticizers. Monomeric (mol wt 250—450) plasticizers (qv) are predominantiy phthalate, adipate, sebacate, phosphate, or trimeUitate esters. Organic phthalate esters like dioctyl phthalate (DOP) are by far the most common plasticizers in flexible PVC. Phthalates are good general-purpose plasticizers which impart good physical and low temperature properties but lack permanence in hot or extractive service conditions and are therefore sometimes called migratory plasticizers. Polymeric plasticizers (mol wt up to 5000 or more) offer an improvement in nonmigratory permanence at a sacrifice in cost, low temperature properties, and processibiHty examples are ethylene vinyl acetate or nitrile polymers. 

Table 8 indicates the compatibiUty of magnesium with a variety of chemicals and common substances. Because the presence of even small amounts of impurities in a chemical substance may result in significantly altered performance, a positive response in the table only means that tests under the actual service conditions are warranted (132). Other factors which may significantly alter magnesium compatibiUty include the presence of galvanic couples, variations in operating temperatures, alloy composition, or humidity levels. 

Resistance is iadicated by yes, ie, laboratory tests have shown enough promise to warrant test under actual service conditions. 

Phase diagrams can be used to predict the reactions between refractories and various soHd, Hquid, and gaseous reactants. These diagrams are derived from phase equiHbria of relatively simple pure compounds. Real systems, however, are highly complex and may contain a large number of minor impurities that significantly affect equiHbria. Moreover, equiHbrium between the reacting phases in real refractory systems may not be reached in actual service conditions. In fact, the successful performance of a refractory may rely on the existence of nonequilibrium conditions, eg, environment (15—19). 

Granular materials are shipped raw or calcined and usually have been ground to a specified screen si2e or si2e distribution. The additives depend on the apphcation and service conditions. These materials are used in constmction, repair, or maintenance of furnaces and vessels. Refractory mortars are used to lay brick of the same composition. These are manufactured wet premixed or dry. 

Special Tests. Even though the American Society for Testing and Materials offers a wide range of test methods, there are other special tests that are imposed upon the manufacturer by consumers, the military, the U.S. Government, and ia some cases local or municipal governments. These tests are generally very specific and are oriented toward particular service conditions. In many iastances, the producers develop special tests within thek laboratories to solve customer problems or predict product or production performance. Many of these tests subsequentiy are adopted by ASTM. 

Industrial Surveys of Refractoy Service Conditions, Committee C-8, ASTM, Philadelphia, Pa. 

Tackifiers are used to increase the tackiness and the setting speed of adhesives. They increase tackiness by softening the poly(vinyl acetate) polymer in the wet and the dry adhesive film. Tackifiers are usually rosin or its derivatives or phenoHc resins. Other additives frequently needed for specific apphcation and service conditions are antifoams, biocides, wetting agents, and humectants. 

Colloidal State. The principal outcome of many of the composition studies has been the delineation of the asphalt system as a colloidal system at ambient or normal service conditions. This particular concept was proposed in 1924 and described the system as an oil medium in which the asphaltene fraction was dispersed. The transition from a coUoid to a Newtonian Hquid is dependent on temperature, hardness, shear rate, chemical nature, etc. At normal service temperatures asphalt is viscoelastic, and viscous at higher temperatures. The disperse phase is a micelle composed of the molecular species that make up the asphaltenes and the higher molecular weight aromatic components of the petrolenes or the maltenes (ie, the nonasphaltene components). Complete peptization of the micelle seems probable if the system contains sufficient aromatic constituents, in relation to the concentration of asphaltenes, to allow the asphaltenes to remain in the dispersed phase. 

Durability. The term "durable" has several meanings, but in the present context it is used to describe an asphalt that possesses the necessary chemical and physical properties required for the specified pavement performance, being resistant to change during the in-service conditions that are prevalent during the life of the pavement. 

The mechanical design of the idler roUs is a function of the particular service under which the conveyor operates. Minimum industrial standards for roU dimensions, bearings, and appHcation criteria for different service conditions have been estabHshed (14). Idler life is deterrnined by a combination of factors such as bearings, seals, shell thickness, load density, and the operating environment. 

With the proper idlers select ed for size and service conditions, the most important step is to locate them properly. For long belts the tension varies considerably, and idlers should be spaced to hold belt sag to reasonable limits along the full length of travel. Too much belt sag can cause a significant power loss, but for most belts of ordinary length it is usu ly satisfactoiy to space idlers fairly closely at the feed... 

Small variations in service conditions may appreciably affect corrosion resistance. Choice of materials is tlierefore guided wherever possible by a combination of experience and laboratory and site tests. 

The incubation period varies widely depending on such factors as crack morphology, water chemistry, and temperature. However, experience in a wide variety of cooling water environments has shown that many stainless alloys develop noticeable attack within 6 months of first being exposed to water. It is rare to see attack initiating many years after equipment commissioning unless service conditions change in the interim. 

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