Instrumentation/control systems corrosion

Other research areas that could improve the effectiveness and economics of flue gas treatment are (1) the development of better instrumentation for system control and (2) the evaluation of superior corrosion-resistant materials. System optimization cannot occur without a good means of system control. Many existing flue gas treatment systems are particularly sensitive to instrument feedback and response. The ability to control closely the operation of these systems could enhance their effectiveness and reliability. The presence of water in flue gas treatment systems... 

The task of purging pipelines for maintenance is almost second-nature to well-experienced operators in this unit. Typically, pipeline clearing is routine and is uneventful. This time, however, the utility dry air system was also being utilized as a source for instrument air in the operating area. Hence, this corrosive material was able to backflow throughout the instrument air system into monitoring and control systems. The backflow created expensive instrument damages. 

In order to simplify and improve the use of the corrosimeter, an expert system has been installed on the corrosimeter itself, for controlling the corrosion rates measured by any single probe, and for verifying that the values, the trends and the transients of such corrosion rates are not anomalous. This expert system is called ERICE (Expert Reasoning Instrument for Corrosive Environments). 

The feed control and instrument trips and alarms on the reactor will allow the process to be operated safely. In the event of failure of the control and trip system, the runaway reaction would be safely vented from the reactor. However, since this would result in a serious toxic and corrosive aerosol emission, the reliability of the trip and control system has to be checked. The use of Hazan allows the frequency of the occurrence of the runaway to be determined, in order to decide whether the frequency of emission is acceptable. 

The sulfuric acid attacks exposed concrete and unprotected surfaces of iron, steel, and copper, resulting in corrosion and deterioration of the exposed vulnerable materials. Electrical and instrumentation systems are particularly vulnerable to low levels of hydrogen sulfide gas. H2S readily attacks copper contacts to form copper sulfide, a poor conductor of electricity. This can cause equipment failure or poor reliability of control systems. 

Rugged instruments based on portable computers are now available from many vendors. These systems, complete with motor-driven robotic devices to manipulate the transducer(s), have created the ability to measure wall thickness of corroded components at tens of thousands of points over 0.1 m, which can be converted into mass loss and pitting rates. This capabihty, coupled with increased precision of field measurements achievable with computer-controlled systems, has made these automated ultrasonic systems well suited for online corrosion monitoring [4]. 

Ill-103. Reactivity control system, reactor shutdown system The function of the mechanical and electrical design shall be described. The description shall include the materials and dimensions and shall be supported by drawings. The reactivity control mechanisms and their instrumentation, such as their position or status (coupled/decoupled), should be presented, together with their insertion time and interlocks. The effects of corrosion, fatigue, neutron doses, etc., on the lifetime of the mechanical and electrical components shall also be discussed. The safety related design parameters should be presented, such as ... 

A second, and more subtle, problem to do with utilities is their potential for process contamination. On one refinery, e.g., the highly toxic and corrosive chemical hydrogen fluoride (HF), which is discussed in Chapter 5, leaked into the instrument air system. This had the effect of spreading HF all around the refinery it was even being vented from instrument lines in the control rooms. 

A factor which previously limited installation of automatic corrosion monitoring systems was the cost of cabling between sensors and control room instrumentation-this was particularly relevant to the electrical resistance (ER) systems. Developments to overcome this have included transmitter units at the probe location providing the standard 4-20 mA output (allowing use of standard cable) for onward transmission to data systems or the use of radio linkage which has been successfully used for other process-plant instrumentation. 

The basic components of a liquid chromatograph cover a wide range of sophistication, features and cost [1-5]. Most systems are modular to provide maximum operating flexibility and frequently fully automated. Advanced materials allow the fabrication of instruments from non-metallic components for enhanced biocompatibility and corrosion resistance in life science and ion chromatography applications. Continuing improvement in design and electronic control provides for ease of use with a wider range of column diameters from semipreparative to packed capillary columns at close to optimum separation conditions. Interest in small-diameter columns stems from their lower... 

Ageing effects may be detected by a change in measurable parameters. For example, increase in temperature or pressure may be an indication of die accumulation of corrosion products in the tube of a heat-exchanger and instrument drift may be an indication of electronic component degradation. Parameters should be measured periodically in a consistent manner and the readings should be compared and assessed. Physical parameters, such as temperature, pressure, flow rate, control rod drop times, radiation level (e.g. neutron and gamma), water quality, are indicators of the state of a system, structure or component. 

Part A gives general guidelines for the design of large commercial fluidized bed reactors with respect to the following aspects (1) solids properties and their effect on the quality of fluidization (2) bubble size control through small solid particle size or baffles (3) particle recovery by means of cyclones (4) heat transfer tubes (5) solids circulation systems (6) instrumentation, corrosion and erosion, mathematical models, pilot plants and scale-up techniques. 

The passivation behavior of a metal is typically studied with a basic electrochemical testing setup (App. D, Basic Electrochemical Instrumentation). When the potential of a metallic component is controlled and shifted in the more anodic (positive) direction, the current required to cause that shift will vary. If the current required for the shift has the general polarization behavior illustrated in Fig. 12.1, the metal is active-passive and can be anodically protected. Only a few systems exhibit this behavior in an appreciable and usable way. The corrosion rate of an active-passive metal can be significantly reduced by shifting the potential of the metal so that it is at a value in the passive range shown in Fig. 12.1. The current required to shift the potential in the anodic direction from the corrosion potential can be several orders of magnitude greater than the current necessary to maintain the potential at a passive value. The current will peak at the passivation potential value shown as (Fig. 12.1). 

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