Seal failures

Loss of sealing fluid for vessel agitator seal. Possible seal failure and emission of flammable or toxic vapors. 

First, one pump running in a parallel system tends to suffer from cavitation because operation to the right of the BF.P indicates that the NPSHr of the pump rises drastically. To survive this condition, you should use dual mechanical seals on these pumps. Dual or double mechanical seals can withstand cavitation better than a single seal. There is a discussion on this in the mechanical seal chapter of this book. Many engineers perceive that parallel pumps are problematic becau.se they appear to suffer a lot of premature seal failure. Parallel pumps deserve double seals even if it s only a cold water system. 

Less heat Generated - Less force between the faces indicates less heat generated. Heat is the principal reason for premature seal failure for two reasons ... 

The easiest way to prevent many unplanned premature seal failures is to use balanced o-ring cartridge designed seals. Most of the seal manufacturers make models incorporating these design features. 

The noise and the seal failure are actually symptoms and not the problem. This is like the electrician blaming the fiise for an overloaded electrical circuit. The problem is the overloaded circuit and the symptom is the burned fiise. Likewise, in the maintenance shop, the noisy pump, the failed seals and bearings arc the Symptom of a problem that probably occurred outside the pump. 

The labyrinth portion of the seal was designed to withstand the static and dynamic differential pressure (in the event of a major seal failure) while passing the minimum volume of purge gas. 

Contamination of the seal by foreign objeets leads to seal failures. The running gap between the primary and mating gas seal rings is typieally around 3 mierons. Injeetion of any type of solids or liquids into this very... 

Equipment in HCl and chlorine service must be protected against the exposure of these acid gases to the oil. Obviously, the first line of defense is to eliminate seal failures. However, as a secondary protection, these machines could be lubricated with an alkaline oil. The alkaline additives react to the low concentrations of the acid gases, thus eliminating the addition of these acids to the oil molecule. 

For the double-opposed seal, normally an inert gas is injected between the two opposed seals. This gas is pressure controlled to maintain a differential pressure higher than the process side pressure. The supply to this seal is critical because a failure will permit the differential pressure across the outer seal to reverse, which will result in a seal failure. This seal arrangement usually incorporates a buffer to the process side of the... 

Reactor coolant pump (RCP) seal failures that lead to a loss of coolant accident (LOCA)... 

This report briefly describes a group of reactor coolant pump (RCP) seal failures that occurred at Arkansas Nuclear Unit 1, Calvert Cliffs Unit 1, and Indian Point Unit 3. Both mechanical and maintenance-induced RCP failure are discussed. For each event, the following information is provided the... 

The report presents the findings from the analysis of the RCP failures. Estimates of the annual frequency for the spectrum of leak rates induced by RCP seal failures and their impact on plant safety (contribution to coremelt frequency) are made. The safety impact of smaller RCP seal leaks was assessed qualitatively, whereas for leaks above the normal makeup capacity, formal PRA methodologies were applied. Also included are the life distribution of RCP seals and the conditional leak rate distributions, given a RCP seal failure the contribution of various root causes and estimates for the dependency factors and the failure intensity for the different combinations of pump designers and plant vendors. 

A mechanical seal s performance depends on the operating condition of the equipment where it is installed. Therefore, inspection of the equipment before seal installation can potentially prevent seal failure and reduce overall maintenance expenses. 

Seal rubbing or Cage wear Cocked races Flatted roller or ball Seal failure... 

Leaking tubes resulting from seal failures... 

In evaluating event frequency, past incidents can provide invaluable guidance. For example, if a pump seal failure is identified as having the potential to lead to a vapor cloud release, and if previous pump seal failures have occurred frequently, it might be reasonable to conclude that such a scenario is likely. This conclusion may be valid even though previous pump seal failures did not result in a vapor cloud. 

Liquids under pressure (pipeline leaks, pump seal failures, etc.), will be thrown some distance from the point source, while atmospheric leakages will emit at the point of release. The other characteristic of liquid releases is their flash points. High flash point liquids, not operating above their flash point temperatures, are inherently safer than low flash point liquids. Most liquid fires are relatively easy to contain and suppress while gas fires are prone to explosion possibilities if extinguished and source points are not isolated. 

Pump seal failure released liquids which ignited. 

Fire hazard analysis (FHA) is the process to determine the size, severity, and duration of a scenario and its impact on personnel, equipment, operations, and the environment. Chapter 5 provided details of performing an FHA. The following paragraphs provide an overview of the FHA process. For example, one scenario could be a seal failure where the material being released is ignited and afire results. In assessing consequences, several questions must be considered ... 

The volumetric gas generation rate, QgLx is calculated as 9.8 m3/s (see A2.5), given the maximum rates of temperature and pressure rise from Table 3.1 before seal failure. 1 ". ... 

This is an underestimate because of the seal failure in the test, but is over 5 times larger than that obtained for case (ii). It can therefore be concluded that case (iii) is the worst case. 

We can see, then, that either condensate backup, or blowing the condensate seal, will cause a steam reboiler to lose capacity. If you think either of these two problems could cause a loss in reboiler duty, try opening the bypass around the steam trap. If the reboiler duty goes up, the problem was condensate backup. If the reboiler duty goes down, then the problem might be a blown condensate seal. If it looks like a blown condensate seal problem, close the steam trap bypass. Then, partially close the valve downstream of the steam trap. If this increases the reboiler duty, a blown condensate seal failure is proved. 

Sometimes two other incidents are attributed to LNG The first one - a construction accident on Staten Island in 1973 - was cited as a LNG accident because work was carried out inside an empty LNG tank. The second - an electrical seal failure on a LNG pump that failed in 1979 - caused an explosion because gas (not LNG) entered an enclosed building. This event gave rise to a thorough revision of the code for electrical seals used with all flammable fluids underpressure [10],... 

Probes can be engineered for almost any environment, but these requirements must be clearly defined before probes are built. No probe can survive all environments so there may be some design trade-offs. Many immersion probes have a second window as a safety backup to ensure the process remains contained in the event of a window seal failure. Probes have been designed with motorized focus adjustments, automatic solvent or steam washes or air jets to keep the window clear, and sealed in water- and pressure-safe containers. Three commercial probes, two immersion and one non-contact, are pictured in Figure 5.4. Different optics can be attached to the face of the non-contact probe, much like conventional cameras using different lenses. 

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