Valve Criticality Analysis

A useful human factors exercise is to conduct a Valve Criticality Analysis. Typically, manually operated valves are organized into categories such as operated daily, operated occasionally, and used only during turnarounds. The category selected will determine the location and accessibility of the valve, with those that are used daily being provided with easy access that does not require any stretching or the use of ladders or other temporary equipment. 

The valve criticality analysis should be conducted by a team. During a project, the analysis will start once the P lDs (piping and instrument diagrams) are available. Team members include the following ... 

As discussed in Section 2, the system (flow control valve) under analysis might go through n states, before reaching the most critical deterioration state -I-1. In this paper, it is used the multiobjective GA integrated... 

Failure modes and effects analysis (FMEA) A systematic, methodical analysis performed to identify and document all identifiable failure modes at a prescribed level and to specify the resultant effect of the failure mode at various levels of assembly (NSTS 22254) the failure or malfunction of each system component is identified, along with the mode of failure (e.g., switch jammed in the on position). The effects of the failure are traced through the system and the ultimate effect on task performance is evaluated. Also called failure mode and effect criticality analysis (ASSE) a basic system safety technique wherein the kinds of failures that might occur and their effect on the overall product or system are considered. Example The effect on a system by the failure of a single component, such as a register or a hydraulic valve (SSDC). 

New systems or processes may also need to be qualified from an operational safety perspective. This is particularly relevant in the case of chemical synthesis involving exothermic reactions. Critical safety aspects are usually identified using hazard operability or HAZOP assessments and studies. For example, a HAZOP analysis of an exothermic reaction vessel would involve consideration of the consequence of failure of the motors for mixers or circulation pumps for cooling water. Thus, the qualification of such a system would involve checks and assessment to ensure that the system/process can be operated safely and that pressure relief valves or other emergency measures are adequate and functional. 

Research has been done showing that rapid pressnre-driven LC analysis can be done with little solvent consumption, demonstrating this as a viable process analytical tool. Using electrokinetic nanoflow pumps LC can be miniaturized to the point of being a sensor system. Developments in terms of sampling to enable sampling directly from a process stream, to the separation channel on a chip are critical for the application of miniaturized process LC. The components (valves and pumps) required for hydrodynamic flow systems appear to be a current limitation to the fnll miniatnrization of LC separations. Detection systems have also evolved with electrochemical detection and refractive index detection systems providing increased sensitivity in miniaturized systems when compared to standard UV-vis detection or fluorescence, which may require precolumn derivatization. 

Is the risk too high to adjust the critical isolation valves while the bullet tank was full of a highly flammable liquid (A Process Hazards Analysis might question the practice.)... 

Phase equilibria and pressure-temperature coordinates of critical points in ternary systems were taken with a high-pressure apparatus based on a thermostated view cell equipped with two liquid flow loops which has been described in detail elsewhere [3]. The loops feed a sample valve which takes small amounts of probes for gas-chromatographic analysis. In addition to temperature, pressure and composition data, the densities of the coexisting liquid phases are measured with a vibrating tube densimeter. Critical points were determined by visual oberservation of the critical opalescence. 

Different implementations of such reactors may differ in detail. For instance, in some cases the flow to the analytical instrument is additionally controlled by a mass flow controller, so that at least during the analysis all catalysts are evaluated at exactly the same space velocity. In other setups, which will be discussed below, a truly parallelized analysis is integrated into the reactor, which allows the elimination of the multiport valve. The general features of such reactors, however, can be summarized as those of a multitubular fixed bed. Critical issues in operating such parallel reactors have been discussed by Moulijn et al. [33], who also had published one of the first prototypes of a parallel reactor, the so-called six-flow reactor [34],... 

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