PATENT
Inventor: Paulo Roberto Leite Nóbrega
Original Assignee: Petróleo Brasileiro S.A.- Petrobras
Patent number: 7878508
Issue date: Feb 1, 2011
Application number: 12/659,233
FIELD OF THE INVENTION 15
The seal is provided by an internal labyrinth which is capable of retaining the lubricating oil within the bearing housing in a 20 highly efficient way and preventing moisture or dirt from entering. It also has very small external dimensions, and can be used as a replacement for the lip seals commonly in use without causing problems to the accessory equipment connected to a pump. 25
DESCRIPTION OF THE RELATED ART
The oil industry, and the various processes which it involves, frequently makes great use of various models of 30 centrifugal pumps.
Once extracted at production platforms, oil passes through a great variety of means of transport, such as oil pipelines or tankers, and in the main, in the process specifically referred to as refining, in specific industrial facilities, it has to be pumped 35 through thousands of metres of pipe and hundreds of systems, which in popular language are known as the processes of oil extraction and refining.
Thus the most important components, and the ones most subject to wear in the oil industry, are pumps, which are used 40 in a variety of applications, and which may be present in a variety of models and power, requiring great attention when specifying and maintaining them.
As these are essential components in any stage of processing in the oil industry, many pumps are used continuously, 45 only being shut down if a fault occurs or for programmed maintenance.
Pumps have bearings within the bearing housing which are sensitive to any contaminant from the environment in which the pump is operating. They also have a component, which is 50 particularly subject to failure, which isolates the bearings within the bearing housing from the external environment, and also prevents any trace of lubricant from the interior of the bearing housing from contaminating the environment.
At the present time many pumps present in industrial facili- 55 ties were originally designed using lip seals as the isolating member, fitted in such a way that they are always located in the space included within the thickness of the bearing housing. They do not occupy any space beyond the internal or external surfaces of the bearing housings, and much operating 60 equipment has been designed accurately to fit these pumps.
However, lip seals have a very short service life and low resistance to the pressure of the oil vapour which can be generated within bearing housings; in some cases lip seals do not last three months' operation. Thus lip seals which have 65 already been fitted need to be replaced by a device which is more efficient and durable, and this is a seal.
In this respect standards have been created to establish minimum parameters to provide maximum satisfaction for these isolating conditions, and which make lip seals obsolete. One of these standards is the American Petroleum Institute Standard API 610, 9th edition (2003), which states:
"5.10.2.7—Bearing housings shall be designed to prevent contamination by moisture, dust and other foreign matter. This shall not be achieved through the use of compressed air injection, but through the use of labyrinth or magnetic-type seals in those places where the shaft passes through the housing".
Nevertheless, complying with this requirement through using a seal of the labyrinth type is also extremely difficult because the majority of these seals available on the market allow oil to flow from the bearing housing under severe operating conditions. The problem is made worse when an attempt is made to use seals dimensioned with reduced thickness as a replacement for old lip seals already fitted in earlier work.
Despite seals of the labyrinth type being slightly cheaper than hermetic seals, having a technically indefinite service life, any failure gives rise to great losses for the petroleum industry, in particular when all the hours during which the production processes involved are shut down during repairs, or the environmental harm resulting from such flows, are taken into account. The costs in man/hours of overcoming all these problems are high, as is also the harm of possible adverse repercussions on a company involved in environmental accidents.
Direct losses have been measured as a result of investigations which demonstrated seal failure in the inward direction, where the presence of only 0.02% of water in the bearing oil was sufficient to reduce the useful life of the bearings by up to 48%. Indirect losses could be even greater, because of the possibility of a seal failure in the inward/outward direction giving rise to an oil leak and causing a company to have a negative image in environmental terms.
Any unscheduled shutdown, especially those caused by failure of the bearing housing seal, not only interrupts the process of which the particular pump is a part but also invariably damages various components of the pump.
There are various models of labyrinth-type seals designed according to current standards, but one of the greatest concerns of the engineers responsible for pump maintenance is to be able to replace the lip seals fitted on former occasions by seals available on the market so as to avoid failures, especially in the case of centrifugal pumps. Labyrinth-type seals, when free from defects, are those most indicated for these applications because of a number of basic considerations.
They are a device having smaller axial dimensions, which allow a greater possibility for adjustment when they replace a lip seal in equipment with little internal space.
The second reason is of an economic nature. As the number of items of equipment which need to be adapted is very high and labyrinth-type seals offer the lowest cost among the seals available on the market, this is the option which generates greatest interest.
Given that every pump needs at least two seals, and that around 1000 pumps are used in a medium-sized refinery, the economic factor caused by the impact of the application of these components is clearly apparent.
Nevertheless the labyrinth seals currently available on the market, despite being a cheap option, have a number of problems which also make their use subject to special attention.
Despite their advantages, some of the labyrinth-type seals most currently in use in the oil industry also have disadvantages which give rise to premature failures or the need for periodical maintenance.
By way of example, one of the labyrinth-type seals most widely used at the present time is the INPRO-VBX®.
Although thin, these seals also have an axial thickness which may cause problems when they are used as replacements for old lip seals. 5
They have already given rise to isolation failures when subjected to severe operating conditions, or even when there is occasionally an excess of lubricating oil in the bearing housing.
Isolation failures have also been detected in the inward/ 10 outward direction, because the passage area in the labyrinth has poor retaining properties. It can be seen that all the labyrinth-type seals currently available on the market have a single deflector located on the outside surface and therefore do not provide any extra protection in the inward/outward 15 flow direction.
Another technical disadvantage encountered in the use of this device is the difficulty of fitting or removing it, because a press has to be used. Apart from the fact that use of a press gives rise to operational difficulties, it may result in alignment 20 problems, which will consequently give rise to a failure of isolation in either direction, inwards or outwards.
Alignment is a condition which is very difficult to achieve in seals for bearing housings with the models currently in existence, because the seat is in a stationary condition, and the 25 primary seal is fixed in a rotating sleeve. In turn present sleeves are provided with a single "O" ring. This construction of the sleeve with a single "O" ring can give rise to misalignment during installation.
In the models currently in existence on the market perfect 30 alignment is only achieved through very careful fitting work, preferably calibrated using a centering-comparison gauge. This is a task which in addition to requiring special tools requires time, and has to be carried out by a specialist engineer. 35
It is also important to point out that being imported products they have an additional cost, in addition to requiring logistics on the part of the stores department so that there is never any shortage, especially in emergency situations.
Thus, no matter how good the quality of the isolation, the 40 alignment and the availability offered by labyrinth-type seals, what would be better would be equipment which is durable. It is because of this that design engineers in the oil industry try to exceed the requirements of API Standard 610, 9th ed. (2003), and create their designs to ensure that the sealing of 45 bearing housings with labyrinth-type seals overcomes the problems currently in existence, especially in centrifugal pumps.
The object of this invention is to provide a labyrinth-type seal for bearing housings which fully meets API Standard 610 50 for this type of seal. Other objectives which the compact restrictive seal for bearing housings to which this invention relates is intended to accomplish are listed below:
a. Improving the seal to prevent oil leaks to the environment,
b. Improving the seal to prevent the entry of contaminants 55 from the environment into the bearing housing,
c. Improving protection against jets of liquids,
d. Improving the seal in situations where there is excess oil in the housing,
e. Reducing the need for specialist professionals to carry out 60 the work of fitting mechanical seals,
f. Eliminating the need for a press to fit the seal,
g. Provision of a longer service life and for the pump in which it is fitted,
h. Easier fitting through self-regulating alignment, 65
i. Fitting with axial adjustment provided by the seal itself, j. A rotary seat,
k. Use of less external space,
1. Possibility of use on pumps, specifically centrifugal pumps, m. Possibility of use in a wide range of rotary equipment such as: electric motors, mixers, reduction gears, turbines, etc.
SUMMARY OF THE INVENTION
This invention relates to a labyrinth-type seal which is easy to fit and remove, it is provided with a double deflector system and a two-function labyrinth system, and which is very much thinner than similar seals present on the market.
The invention comprises a set of known elements such as: sleeve, housing, labyrinths, sealing "O" rings, resilient rings and deflectors, arranged in such a way that their special configurations and construction features make it possible to produce a labyrinth which brings about maximum restriction of communication between the internal environment and the external environment of the bearing housing, and when fitted has a total thickness which is very much less than that of the seals currently in existence.
In its general lines the assembly is arranged as follows:
A circular sleeve with a profile of recumbent "J" shape in which the longer limb is parallel to the axis and whose free extremity is directed away from the bearing housing.
The next element forming the compact restrictive seal is a housing in which an expanding restraining ring and a centralising ring are fixed. The housing has a "J"-shaped profile in cross-section, with the longer limb parallel to the axis and pointing towards the interior of the bearing housing, where it is fixed. This longer portion of the housing is subdivided into two sections with specific functions, namely the first section is distinguished in that it is totally beneath the projection of the wall of the bearing housing and the second section is outside the bearing housing.
The inner face of the first section is provided with two successive channels; the expanding restraining ring is mounted in one of the channels so that the expanding restraining ring together with the subsequent channel, the smaller portion of the sleeve and the free extremity of the vertical portion of the said sleeve together form an internal labyrinth and an internal drainage chamber over the entire internal perimeter of the seal.
The second section does not wholly face the outer wall of the bearing housing, but is slightly separated from the outer wall of the said bearing housing by a tooth, thus forming a channel between the outer wall of the bearing housing and the outer body of the seal.
The vertical portion of the said housing has a shape which mirrors the inner face of an external deflector, and has at least one main channel which together with a tooth form an external drainage half-chamber. The free extremity of the shorter portion of the same housing, also in a direction parallel to the axis, faces the interior of the bearing housing.
The said free extremity of the shorter portion is provided with a toothed cavity around the entire perimeter of the housing, and a centralising ring, preferably comprising a polymer alloy, is fixed to this toothed cavity.
The final component of the seal which has to be connected is the external deflector, which has a closed circular shape, with an "L"-shaped profile in cross-section, its longer portion lying perpendicular to the axis and its free extremity having a "V"-shaped bevel, a tooth is provided downstream. This profile presented by the longer limb of the external deflector combines with the matching profile of the main channel and the tooth of the vertical portion of the housing.
The shorter portion of the external deflector parallel to the axis is provided with two channels, one at each extremity of 30
the segment of the portion. The innermost channel is configured to seat the "O" sealing ring and the outermost channel houses a restraining ring. After the seal has been fitted the said ring is located in an intermediate position between the outermost channel and the sleeve channel. 5
No comments:
Post a Comment