Corrosive condition, prevention

If the performance of the equipment is monitored on a continuous basis, then abnormal behaviour can be identified, and preventive maintenance can be performed as and when required this is called on-condition preventive maintenance. The condition of equipment may be established by inspection, that is taking it off-line, opening it up and looking for signs of wear, corrosion etc. This obviously takes the equipment out of service, and may be costly. 

Any acoustic treatment on the fan discharge is required to operate under potentially corrosive conditions, with warm moist air passing through the attenuators. Precautions are needed to ensure that these are adequately treated to prevent risk of condensation and that the structural media are also protected against water pick-up and potential damage. 

A compressor will always give better, more reliable service when enclosed in a building that protects it from cold, dusty, damp, and corrosive conditions. In certain locations, it may be economical to use a roof only, but this is not recommended unless the weather is extremely mild. Even then, it is crucial to prevent rain and windblown debris from entering the moving parts. Subjecting a compressor to adverse inlet conditions will dramatically reduce reliability and significantly increase maintenance requirements. 

Relief valves are preferred for use on clean materials, because automatic closure prevents excessive discharge once excessive pressure is relieved. Rupture disks are less susceptible to plugging or other malfunctions but may allow complete emptying of the vessel, thus creating a safety or environmental hazard. Where fluctuating pressures or very corrosive conditions exist, or where polymerizable materials could prevent proper operation of a relief valve, some designers install two safety devices in series, ie, either two rupture disks or an upstream rupture disk followed by a relief valve. With either arrangement, it is imperative that the space between the two relief devices be monitored so that perforation or failure of the relief device closest to the vessel may be detected (86). 

Description Ammonia and carbon dioxide react at 150 bar to yield urea and ammonia carbamate. The conversion in the reactor is very high due to favorable NH3/CO2 ratio of 3.5 1 and operating temperature of 185°C to 190°C. These conditions prevent corrosion problems. Carbamate is decomposed in three stages at different pressures in the stripper at the same pressure as the reactor, in the medium-pressure decomposer at 18 bar and in the low-pressure decomposer at 4.5 bar. 

To this concern. Figure 20.5 shows the results of application of cathodic prevention to slabs subjected to ponding with a NaCl solution [43]. After about 700 days, initiation of rebar corrosion was detected in the control slab (in the free corrosion condition) at spots where the chloride content at the steel surface had reached more than about 1 % by mass of cement. From about that point in time, the slab receiving a very low current density of 0.4 mA/m showed a similar (instant-off) potential as the control slab and its 4-hour decay values became lower than 100 mV. The slab receiving 0.8 mA/m showed lower decays from about... 

Thermogalvanic corrosion is prevented by appropriate design and measures to avoid uneven heating/cooling and forming of hot spots. For heat-insulated pipes and equipment is important that the insulation is continuous. The corrosion form may under certain conditions be prevented by cathodic protection or coatings. 

An important factor that should be taken into account while drying PVC is the corrosion of the equipment due to the monomer chloride. Monomer chloride, which is always present in the wet cake, induces pitting corrosion and stress corrosion cracking in parts where the powdery materials are processed. Those parts, therefore, are made of AISI-316L and are partially coated with an acid-resistant coating. It is indispensable to make periodic inspection of the corrosion condition and to make timely replacement of the necessary spare parts. Preventive maintenance is imperative to successful operation. 

Recognize corrosion problems in materials used at the site and make monitoring a normal part of the operation. Sour oil and gas operations are often conducted under high pressure and corrosive conditions. Therefore, in addition to temperature and pressure considerations, system designs for the wellhead, downhole equipment, and pipeUnes must have features to minimize the effects of corrosion and prevent an accidental release of H2S. Corrosion-inhibiting fluids can be used to prevent internal corrosion and cathodic protection can be used to prevent external corrosion. Also, during extended periods of shut-in and injection into pipelines, inhibitor applications may be beneficial. 

The issue of carbon corrosion has received considerable attention in recent years. There are several drivers for this (1) the cost drivers for commercialization require the use of high performance catalysts with less durable carbon catalyst supports, (2) the need for system simplification and low cost prevents additional control systems to be implemented to avoid the carbon corrosion conditions, and (3) the use of the fuel cells subjected to "real world" conditions as opposed to carefully controlled demonstration projects, with very dynamic duty cycles and many start-up/shutdown cycles. This increased attention has resulted in new or improved measurement techniques and several studies and reviews on the high cathode potential and associated carbon corrosion mechanism [39,40,48-51]. 

The importance of ensming that the specification and selection of electrical equipment is appropriate to the environment and conditions of use is recognised in the W Regulations. Regulation 6 specifically mentions various kinds of adverse or hazardous environments, namely the effects of the weather, natural hazards, temperature, pressure, wet, dusty and corrosive conditions as well as exposure to flammable or explosive dusts, vapoms or gases. The requirement is that electrical equipment which may reasonably foreseeably be exposed to such conditions shall be of such construction, or as necessary protected, as to prevent, so far as is reasonably practicable, danger arising from such exposure. 

Regulation 6 has the important stipulation that measures must be taken to prevent dangerous deterioration of equipment that may be exposed to conditions that may adversely affect its performance. The specific influences considered are mechanical damage the effects of the weather, natural hazards, temperature or pressure the effects of wet, dirty, dusty or corrosive conditions and any flammable or explosive substances, including dusts, vapours or gases. 

Most inhibitors are required to function in aqueous environments in various states of aeration. Furthermore, there may be a requirement for them to be added to an environment to help prevent the further development of corrosion. The data referred to above were obtained in quiescent NaCl solutions open to air. The performance of R salt inhibitors under various conditions of aeration, i.e. alternate immersion, constant immersion in a quiescent test solution and constant immersion in an aerated test solution, has been studied by Hinton (1989). The weight-loss data obtained for tests with 7075 Al alloy in 0.1 M NaCl containing 1000ppm CeCls are shown in fig. 6. The R salts are effective inhibitors even under the most severe corrosion conditions, some of which are typical of service conditions. For example, the inhibition efficiency is greatest in a continuously aerated solution. This is consistent with a mechanism of inhibition based on the formation of the R oxide on the metal surface (see sects. 2.6 and 2.8). Continuous aeration will favour the reduction of oxygen with the formation of hydroxyl ions, and consequently promotes the precipitation of the R oxide and its coverage of the metal surface. 

This attack occurs when pH is either very high or very low. The protective aluminum oxide layer dissolves rapidly under the above conditions. Prevention from uniform corrosion requires control of pH by inhibitor additions, or use of cathodic protection, or replacement with a more corrosion-resistant alloy. 

Where protection is reqnired against atmospheric corrosion only (e.g. nnder rural conditions), it may not be necessary to use sealer, provided an adequate fihn thickness of sacrificial metal contained, for example, in a metalhc or inorganic zinc coating, is applied. Otherwise an apphcation of sealer is a necessity, observing that it is in the interests of the proprietor of a utihty to avoid repetition of expensive overall preparation of surface. Sealer extends the effectiveness of anti-corrosive composition and the anti-corrosive composition prevents the onset of corrosion that penetrates through damaged and porons sealer. Both are complementary to each other. 

A comparable effect to the sacrificial electrodes is provided by the direct supply of a cathodic current to the dissolving metal. A proper cathodic current applied to the metal structure sets the potential to a value where corrosion is prevented. A disadvantage is the requirement of a permanent cormection to a current supply (or even a potentiostat). However, with this approach, the metal construction may be tuned in for complicated situations. Metallic structures often consist of several metals with different corrosion properties. The environmental conditions may be very difficult. For example, passivation should be maintained but the potential should not become more positive than the critical pitting potential. In these complicated cases, a potentiostat with a CE and a RE is useful. The WE of this circuit is the metal construction. Protection by a current source is applicable to chemical reaction vessels or constructions with permanent location but not always to mobile devices like cars, ships, etc. Therefore both methods are useful, and the choice depends on the specific requirements for the construction in service conditions. In well-conducting electrolytes, one has to take care of the equilibrium potentials of the involved electrodes (metal/metal ion and redox electrode). If the environment has a low conductivity (wet soil), ohmic drops have to be taken into account in order to establish an appropriate protecting... 

The temperature and humidity should be maintained at comfort conditions consistent with the operator s expected level of activity in order to minimise perspiration. Constant temperature and humidity may also be required in machine rooms to prevent the etching or corrosion of machine parts. If perspiration causes only minor damage to the product and results in few rejects, then inside design conditions at 27°C and 40% rh are satisfactory. Where even small amounts of perspiration cause extreme damage to precision-machined parts and result in a high amount of rejects, inside design conditions of 21°C and 40% rh are recommended. 

Bronze disease necessitates immediate action to halt the process and remove the cause. For a long time, stabilization was sought by removal of the cuprous chloride by immersing the object in a solution of sodium sesquicarbonate. This process was, however, extremely time-consuming, frequentiy unsuccesshil, and often the cause of unpleasant discolorations of the patina. Objects affected by bronze disease are mostiy treated by immersion in, or surface appHcation of, 1 H-henzotriazole [95-14-7] C H N, a corrosion inhibitor for copper. A localized treatment is the excavation of cuprous chloride from the affected area until bare metal is obtained, followed by appHcation of moist, freshly precipitated silver oxide which serves to stabilize the chloride by formation of silver chloride. Subsequent storage in very dry conditions is generally recommended to prevent recurrence. 

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