Possible Cause

Check the instrumentation in a systematic manner in search of the leak. It is useful to check the flow rate at this point by placing a measuring 

Note Before disconnecting any of the tubing, ensure that the pump is switched off. A sudden release in system pressure may result in a fine, high-pressure jet of mobile phase, which can pose health and safety risks. 

If reconnecting the column fails to correct the leak, then other common areas to search for leaks are the detector flow cell, the pump (around the pistons), and the injector valve. The same process should be followed until the source of the leak is identified and corrected. New parts maybe required for example, the pump piston seals may have worn out. Always consult the manufacturer s user manual when attempting to replace any part. If in doubt, contact the manufacturer and ask for installation of the new part. It will be necessary to undertake system performance qualification on the replacement of any worn out or damaged part (see Chapter 8). 

Some HPLC systems have leak detectors placed at strategic locations on the system, which can be invaluable in this sort of situation. A leak on these systems is often accompanied by a red warning light and a pump shutdown. Although quite obvious, another useful diagnostic tool is to look for a small deposit of mobile phase around or under the HPLC system. It is easier to see this when the area around the HPLC is kept clean and tidy, and good housekeeping practice at all times is recommended. 

Small pools of mobile phase can be a common occurrence when buffers are used in the mobile phase. Where there are high concentrations of 

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Item Study node Process parameters Deviations (Guide words) Possible causes Possible consequences Action required Assigned to i i... 

Parasitic ferromagnetism is a weak ferromagnetism that accompanies antiferromagnetism, eg, in a-ferric oxide [1309-37-1], a-Fe202. Possible causes include the presence of a smaU amount of ferromagnetic impurities, defects in the crystal, and slight deviations in the directions of the plus and minus spins from the original common axis. 

Equation 7 shows that as AP — oo, P — 1. The principal advantage of the solution—diffusion (SD) model is that only two parameters are needed to characterize the membrane system. As a result, this model has been widely appHed to both inorganic salt and organic solute systems. However, it has been indicated (26) that the SD model is limited to membranes having low water content. Also, for many RO membranes and solutes, particularly organics, the SD model does not adequately describe water or solute flux (27). Possible causes for these deviations include imperfections in the membrane barrier layer, pore flow (convection effects), and solute—solvent—membrane interactions. 

Diuretics, such as those of the thiazide type, have been the cornerstone of first-line antihypertensive treatments for decades. However, popularity and use have eroded as a result of increases in sudden death in patients on diuretic therapy, and unfavorable effects on blood Hpids profile, ie, increasing cholesterol and triglyceride. These effects have been impHcated as possible causes for the lack of decrease in the mortaUty rate resulting from acute MI in patients treated with a diuretic (187,240,241). However, diuretics do protect against stroke and CHF. 

There are many chemicals, by lowering suitable as carriers. Their bp is one of the principal criteria in selection. If bp is too low, the compound will evaporate from the dyebath at dyeing temperatures, and will be lost before it is effective in its role as a carrier. It may also steam distill (condense on the cooler parts of the equipment) and cause drips that will spot the fabric. On the other hand, if the bp is too high, the compound cannot be removed from the fabric under normal plant drying conditions and will affect lightfastness of finished goods, leave residual odor, and possibly cause skin irritation to the wearer. 

As the mechanical integrity of the pump system changes, the amplitude of vibration levels change. In some cases, in order to identify the source of vibration, pump speed may have to be varied, as these problems are frequency- or resonance-dependent. Pump impeller imbalance and cavitation are related to this category. Table 10-11 classifies different types of pump-related problems, their possible causes and corrective actions. 

Hygroscopic materials, condensation of moisture, or tarry adhesive components possibly causing crusty caking or plugging of the fabric or requiring special additives... 

Particulates deposition possibly causing plugging of the bed or plates... 

The current and past operation should be compared so that the timing of the observed problems is estabhshed. The possible causes (hypotheses) can be compared against the measurements found on the log sheets. The number of possible causes can then be reduced. When the quantity or quahty or measurements is insufficient to further reduce the set of causes, additional measurements are required. These may require special instruments (e.g., gamma-ray scanning) not routinely usedin the plant. Alternative operating conmtions may also be required to further reduce the number of causes. As part of the problem identification, it is alwavs important to look for measurements that are inconsistent with the proposed explanation. They will be more informative than the ones justifying the hypothesized cause. Ultimately, with appropriate additional measurements, the cause can be identified. This is not an exact science and, as stated above, relies heavily upon the communication, technical, and investigative skills of analysts. 

At this point in the investigation, the relationship between the pits and the arrowhead-shaped regions of corrosion was uncertain. Several possible causes for the pitting were considered, such as siphonic gas exsolution, biological and/or microbiological activity, and debris (concrete chips, etc.) lodged in the tubes, but each was tentatively dismissed as improbable since none of the proposed mechanisms adequately accounted for all observations. 

So in this chapter of failure analysis and corrective methods, we decided to consider some problems, symptoms, and remedies particular to PD pumps. We re using two tables. The first table lists the few symptoms that send a PD pump into the shop. These symptoms are mated to another column of possible causes listed in numerical order. The numerical causes are on the second tabic starting with the. source of the problem in the left column and the probable cause/suggested remedy in the right column. As you go through the list, you ll see again that PD pumps and centrifugal pumps have a lot in common. Enjoy. 

There have been some indications, although controversial, of increased precipitation downwind of major metropolitan areas. Urban addition of nuclei and moisture and urban enhancement of vertical motion due to increased roughness and the urban heat island effect have been suggested as possible causes. 

Troubleshooting is described by suggesting possible causes of the more common problems and discussing corrective measures. 

The glycol pH should be controlled to avoid equipment corrosion. Some possible causes for a low, acidic pH are ... 

Several structural factors have been considered as possible causes of the anomeric effect. In localized valence bond terminology, it can be recognized that there will be a dipole-dipole repulsion between the polar bonds at the anomeric carbon in the equatorial conformation. This dipole-dipole interaction is reduced in the axial conformation, and this factor probably contributes to the solvent dependence of the anomeric effect. 

Consider possible cause at building design, construction and commissioning stages Bake out buildings to drive out pollutants... 

The marketing information primarily identifies either problems or opportunities. Problems will relate to your existing products and services and should indicate why there has been a decline in sales or an increase in returns. In order to solve these problems a search for possible causes should be conducted and one valid method for doing this is to use the Cause and Effect Diagram. Opportunities will relate to future products and services and should indicate unsatisfied wants. There are three ways of collecting such data by observation, survey, and experiment. 

Having collected the data you will need to sort it and manipulate it so as to reveal the significance of the nonconformities and theorize about the possible causes. There may be several causes, in which case there will be some that dominate the others. Your job is to discover the dominant cause of the nonconformity and test the theories to find the actual cause, using problem-solving methods (see below). 

Silica gels will shatter in the presence of free water and are chemically attacked by many corrosion inhibitors. The chemical attack permanently destroys the silica gels. The other desiccants are not as sensitive to free water and are not chemically attacked by most corrosion inhibitors. However, unless the regeneration temperature is high enough to desorb the inhibitor, the inhibitor may adhere to the desiccants and possibly cause coking. 

The rupture discs on some water compressors were allov/ed to discharge inside a building as the water was clean. However, by the time it had drained down through several floors to the basement of the building, it had dissolved some solid material that had been spilt on one of the intervening floors and became hazardous. Discs had failed on several occasions, for unknown reasons. Possible causes were vibration, hammer pressure, and low-cycle fatigue. 

The worker may have misheard instructions issued by the supervisor and thought that valve B was the required valve. Possible cause communications failure giving rise to a mistaken intention. 

The worker closed valve B very frequently as part of his everyday job. The operation of A was embedded within a long sequence of other operations that were similar to those normally associated with valve B. The worker knew that he had to close A in this case, but he was distracted by a colleague and reverted back to the strong habit of operating B. Possible cause intrusion of a strong habit due to external distraction (correct intention but wrong execution). 

The worker knew that valve A had to be closed. However, it was believed by the workforce that despite the operating instructions, closing B had a similar effect to closing A and in fact produced less disruption to downstream production. Possible cause violation as a result of mistaken information and an informal company culture to concentrate on production rather than safety goals (wrong intention). 

Several examples have already been provided of the use of cognitive models of error to evaluate the possible causes of accidents that have already occurred. This form of retrospective analysis performs a vital role in providing information on the recurring underlying causes of accidents in which human error is implicated. The advantage of an analytical framework driven by a model of human error is that it specifies the nature of the questions that need... 

The second possible cause of nonlinearity is a change in mechanism. Within a reaction series any change in mechanism must be such as to provide a smaller free energy of activation for the reaction (otherwise the mechanism would not change). If a substituent effect can produce a change in mechanism, the result must therefore be curvature that is concave upward. Figure 7-2 is a per plot for the S l solvolyses... 

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