Common causes

The most common causes of abnormally pressured reservoirs are... 

Splitting is most commonly caused by the interaction of protons on adjacent carbons with the proton of interest. If there are m equivalent hydrogens on an adjacent carbon, the proton of interest produces m + 1 peaks by this coupling. 

Sources of Error. pH electrodes are subject to fewer iaterfereaces and other types of error than most potentiometric ionic-activity sensors, ie, ion-selective electrodes (see Electro analytical techniques). However, pH electrodes must be used with an awareness of their particular response characteristics, as weU as the potential sources of error that may affect other components of the measurement system, especially the reference electrode. Several common causes of measurement problems are electrode iaterferences and/or fouling of the pH sensor, sample matrix effects, reference electrode iastabiHty, and improper caHbration of the measurement system (12). 

Vents and flares are intended to take contaminants released from safety valves away from work areas. However, if an elevated vent is at the level of an occupiable platform on the same or an adjacent unit, a worker may, under certain wind conditions, be subject to the nearly undiluted effluent of a vent. Whereas such elevated platforms may rarely be occupied, a heavy exposure from a vent could incapacitate a worker or cause a fall. Tanks that vent only when being filled are common causes of this concern. The usual solution is to raise the vent above any occupiable platform or, at greater cost, to scmb the vent effluent. 

Artificial Hearts. Congestive heart failure (CHF) is a common cause of disabiHty and death. It is estimated that three to four million Americans suffer from this condition. Medical therapy in the form of inotropic agents, diuretics (qv), and vasofilators is commonly used to treat this disorder (see Cardiovascularagents). Cardiac transplantation has become the treatment of choice for medically intractable CHF. Although the results of heart transplantation are impressive, the number of patients who might benefit far exceeds the number of potential donors. Long-term circulatory support systems may become an alternative to transplantation (5). 

Comphcations associated with lUDs include uterine perforation and pelvic inflammatory disease (95). Uterine bleeding and cramping are the most common causes for discontinuation of this method. 

Often, complete mixing cannot be approached for economic reasons. Inactive or dead zones, bypassing, and limitations of energy input are common causes. Packed beds are usually predominantly used in plug flow reactors, but they may also have small mixing zones... 

When a pulsation frequency coincides with a mechanical or acoustic resonance, severe vibration can result. A common cause for pulsation is the presence of flow control valves or pressure regulators. These often operate with high pressure drops (i.e., high flow velocities), which can result in the generation of severe pulsation. Flashing and cavitation can also contribute. 

Identification and quantitative estimation of common-cause failures are general problems in fault tree analysis. Boolean approaches are generally better smted to mathematically handle common-cause failures. 

A common cause of a BLE T] in plants of the hydrocarbon-chemical industry is exposure to fire. With an external fire below the liquid level in a vessel, the heat of vaporization provides a heat sink, as with a teakettle evolved vapors exit tnrough the relief valve. But if the flame impinges on the vessel above the liquid level, the metal will weaken and may cause the vessel to rupture suddenly, even with the relief valve open. The explosive energy for a BLE T] comes from superheat. This energy is at a maximum at the superheat hmit temperature. (SLT is the maximum temperature to which a hquid can be heated before homogeneous nucleation occurs with explosive vaporization of the hquid and accompanying overpressure.) The SLT... 

Active attack is commonly caused by microorganisms. Four factors must be present for a diagnosis of microbiologically influenced corrosion ... 

A common cause of erosion is partial obstruction of tubes by foreign bodies. At the inlet end, for example, debris such as sticks, glass fragments, and wood chips may lodge in tube ends or be held against the tubes by water flow. The nominal velocity of the water past the obstruction increases according to the degree of obstruction. It can be shown... 

Selective removal of nickel from copper alloys is common. However, denickelification does not commonly cause the affected component to fail. Rather, the liberated nickel may deposit downstream and/or be released into the environment. 

Take common cause failures into account while evaluating reliability... 

Use staggered proof testing to reduce chances of common cause failure... 

Eliminate common cause electrical failures for supply and backup... 

Electrical, electromagnetic, or radio frequency interference causes malfunction of the BPCS and SIS. Potential for common cause failure. 

Among the most common causes of premature bearing failure are the following ... 

Improper procedure when mounting the bearing on the shaft is one of the most common causes of premature failure. Roller bearings and ball bearings are precision devices, and correct installation... 

Obviously, oil leakage may be caused by leaking mechanical seals. In turboexpander compressors, however, the most common cause is improperly designed labyrinth seals. Tapered labyrinth designs seem more prone to suffer from this defect. 

Common-cause or inherent variability is due to the set of factors that are inherent in a machine/process by virtue of its design, construction and the nature of its... 

When only common-cause variability is present, the process is performing at its best possible level under the current process design. For a process to be capable of producing components to the specification, the sum of the common-cause and assignable-cause variability must be less than the tolerance. 

High or low fuel gas pressure ean have a dramatic effect on the operation of a firetube heater. Burners are typically rated as heat output at a specified fuel pressure. A significantly lower pressure means inadequate heat release. Significantly higher pressure causes overfiring and over heating. The most common causes of a fuel gas pressure problem are the failure of a pressure regulator or an unacceptably low supply pressure. 

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