FIELD OF INVENTION:
The present invention relates to a steam strainer assembly in steam turbine and more particularly a steam strainer for prohibiting unwanted solid particles or foreign matter to come in contact with steam turbine and thereby saving the blades from severe damages.
BACKGROUND OF THE INVENTION:
Steam turbine is a heat engine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft to drive an electrical generator and hence to generate electricity.
In a typical larger power stations, the steam turbines are split into three separate stages, the first being the High Pressure (HP), the second the Intermediate Pressure (IP) and the third the Low Pressure (LP) stage, where high, intermediate and low describe the pressure of the steam. The High Pressure (HP) turbine is the first turbine to receive steam from the main steam system, while Low Pressure (LP) turbine is the last. The turbine in between the HP and LP is an intermediate Pressure (IP) Turbine, These turbines are designed to efficiently extract work out of high pressure steam.
Even particles of this size can cause serious blading damage. It is therefore essential that a thorough steam blow of all pipework is carried out before a turbine set is commissioned. The risk of damage to new plant from debris, pieces of weld metal, etc., which may be swept through the pipe, used to be minimised by fitting extra-fine commissioning strainers in place of the steam strainers. However, because of the time associated with strainer removal, the modern practice is to rely on the steam strainers to trap all debris.

Precise system control is required for the operation of modern superheated steam turbines. Solids in the steam leaving a boiler can deposit in the superheater and turbines causing damage. For this reason, close control of steam purity is critical.
Steam purity refers to the amount of solid, liquid, or vaporous contamination in the steam. High-purity steam contains very little contamination.
Normally, steam purity is reported as the solids content. Steam purity should not be confused with steam quality as the steam quality is a measure of the amount of moisture in the steam. It is expressed as the weight of dry steam in a mixture of steam and water droplets. For example, steam of 99% quality contains 1% liquid water.
Carryover is any solid, liquid, or vaporous contaminant that leaves a boiler steam drum with the steam. In boilers entrained boiler water is the most common cause of steam contamination. The entrained boiler water contains dissolved solids and can also contain suspended solids. There are many causes of boiler water entrainment in steam.
Boiler water solids carried over with steam form deposits in non return valves, superheaters, and turbine stop and control valves. Carryover can contaminate process streams and affect product quality.
Superheated steam turbines are particularly prone to damage by carryover. Sticking of governor and stop valves due to deposits can cause turbine overspeed and catastrophic damage. Solid particles in steam can erode turbine parts, while deposition on turbine blades can reduce turbine efficiency and turbine capacity. When large slugs of boiler water

carry over with steam, the resulting thermal and mechanical shock can cause severe damage.
Loss of production may result from reduced capacity or equipment failure caused by carryover. In some instances, the effect of carryover on production overshadows all other considerations. Carryover can never be eliminated completely. Even the best boiler designs operating with well controlled water chemistry produce trace amounts of carryover.
With increase in intermediate pressure parameters, designing of Steam strainer housing becomes difficult and the design modification and change in material to keep the design safe in operation is required.
In addition to the above, it is substantially more difficult to manufacture a strainer housing using conventional machining technologies, for example boring, turning, milling, welding etc. This however is also very cost intensive.
Hence, there is always a long felt need to provide an improved steam strainer assembly which can screen different types of particles with efficiency and yet cost effective.
The present invention meets the long felt need.
OBJECTS OF THE INVENTION:
It is therefore, the principal object of the present invention to provide a novel steam strainer assembly which can trap all debris such as solid, liquid or vaporous contamination in the steam.

Another object of the present invention is to provide a steam strainer assembly which is specially designed for modern superheated steam turbines wherein close control steam purity can be achieved.
Yet another object of the present invention is to provide a steam strainer assembly which saves turbine steam from contamination with carry over.
Another object of the present invention is to provide a steam strainer assembly to check erosion of turbine parts and subsequently enhance the turbine efficiency and turbine capacity.
Another object of the present invention is to provide a steam strainer assembly which suffices the requirement of holding the steam strainer and carrying steam from boiler to IP turbine.
Yet another object of the present invention is to provide a steam strainer assembly which is suitable for casting materials.
SUMMARY OF THE INVENTION:
The present invention relates to a steam strainer assembly for steam turbine for trapping all debris, the assembly comprising: an inlet and outlet portions; a steam strainer housing (1) to transfer and clean the steam coming from boiler to turbine; a steam strainer (2) is welded over the blanking device (3) of said housing (1); a graphite gasket (4) is provided into said housing (1) after a protective ring (5) has been inserted into said housing; a segmental split ring (6) is provided at the slot in the said housing to protect blanking device (3), graphite gasket (4) and protective ring (5) from falling a tightening cover (7); and a drain stub (11) for drainage of coller condensed steam.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
Figure 1 illustrates the perspective view of the proposed steam strainer Housing assembly in first angle projection.
Figure 2 illustrates the perspective 3-dimensional view of the proposed Steam strainer Housing assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The subject matter disclosed herein relates to steam strainer placed in a steam strainer housing of steam turbine. Further, the steam strainer actually traps all the debris and any foreign particles to provide substantially high-purity steam with very little contamination.
The steam strainer has been placed at the strainer housing which facilitates the holding of steam strainer and steam from boiler to IP turbine. Particularly, the steam strainer has been installed in the pipe line from the boiler to protect the admission elements of the turbine from foreign objects which could be picked up in the boiler or associated piping. The steam strainer is located inside the strainer housing before

the stop valve, has many small diameters from 2 to 4 mm depending on the manufacturer.
Steam Strainer Housing is a critical component of a steam turbine. In
steam strainer housing, steam strainer is placed to clean the steam
coming from Boiler and supply the steam to turbine for power
production.
The inner contour of the strainer housing has been designed in such a way so that removal of strainer element and clanking plate during overhaul can be achieved successfully.
Further, the strainer housing has been subjected to metal casting and hence the geometry of the housing is selected in accordance with that. The metal casting has performed with a metal object formed when molten metal is poured into a mold which contains a cavity of the desired shape and is allowed to solidify. The casting process is used most often to create complex shapes that would otherwise be difficult or impossible to make using conventional manufacturing practices. Casting geometry is the most powerful tool available to improve castability of the alloy and mechanical stiffness of the casting. Carefully planned geometry can offset alloy problems in fluid life, solidification shrinkage, pouring temperature and slag or dross forming tendency. Section modulus, an attribute of structural geometry, has the capability to increase stiffness and/or reduce stress – a capability that can be very important when applied to alloys with lower strength and stiffness. Modulus of elasticity, an alloy's inherent stiffness, can be combined with section modulus and section length to limit or allow deflection in a casting design. Therefore geometric considerations have been taken while designing the said steam strainer housing such that it remains castable and meets all the requirements of a steam strainer housing.

Figure 1 illustrates an inlet (12), outlet (13) and an area of blanking plate of steam strainer housing (1). Further, the neck radius is kept in such a way that redistribution of stress in neck area is possible.
According to an implementation of the present subject matter, a steam strainer housing (1) has been provided between the steam pipe and the interceptor valve to transfer and clean the steam coming from boiler to turbine. A steam strainer (2) is welded over the blanking device (3) of the housing. The steam strainer has both the provision of being fixed inside the housing (1) or can be uplifted by an assembly device inside the housing (1).
When the strainer (2) gets fixed inside the housing (1), some other equipments such as graphite gasket (4) been inserted after a protective ring (5) in the housing (1) at their respective slot.
Further, a segmental split ring (6) is also placed in the housing (1) to protect the blanking device (3), graphite gasket (4) and protective ring (5) from falling and keeps them tightly at their respective positions.
After that a tightening cover (7) is also provided into which studs (8), washer (9) and nuts (10) have been inserted to tighter the final assembly.
In another embodiment of the present subject matter, a drain stub (11) has been welded with the blanking device (3). It (11) protrudes from the bottom of the housing (1) which further connects to the drain pipe and also helps in drainage of collected condensed steam. The steam comes from boiler though pipe and after passing from the strainer housing, filtered steam goes to the turbine through IVCV valves.

Further, Figure 2 illustrates the three-dimensional view of the steam strainer assembly.
The further non-limiting advantages of the present subject matter has been given below:
i) The housing assembly has been constructed in such a way the end diameters match with pipe diameter keeping the stresses to least values.
ii) The steam strainer assembly helps to optimize fillet in neck and where contours changes in the Housing in such a way that stresses are minimum.
iii) The inner contour of strainer housing facilitates easy removal of strainer element and blanking plate to be possible during overhaul.
Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system or device of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.

WE CLAIM:
1. A steam strainer assembly for steam turbine for trapping all debris,
the assembly comprising:
an inlet (12) and outlet (13) portions;
a steam strainer housing (1) to transfer and clean the steam coming from boiler to turbine;
a steam strainer (2) is welded over the blanking device (3) of said housing (1);
a graphite gasket (4) is provided into said housing (1) after a protective ring (5) has been inserted into said housing;
a segmental split ring (6) is provided at the slot in the said housing to protect blanking device (3), graphite gasket (4) and protective ring (5) from falling;
a tightening cover (7); and
a drain stub (11) for draining of cooler condensed steam.
2. The steam strainer assembly as claimed in claim 1, wherein said steam strainer housing (1) is connected between steam pipe and interceptor valve.
3. The steam strainer assembly as claimed in claim 1, wherein said steam strainer can be uplifted by an assembly device inside the said housing (1).
4. The steam strainer assembly as claimed in claim 1, wherein said tightening cover (7) further comprises studs (8), washer (9) and nuts (10) to tighten the whole assembly.
5. The steam strainer assembly as claimed in claim 1, wherein said drain
stub (11) is welded with the blanking device (3).

6. The steam strainer assembly as claimed in claim 1, wherein said drain stub (11) protrudes from the bottom of the said housing (1), which further connects to the drain pipe.
7. The steam strainer assembly as claimed in claim 1, wherein strainer element and blanking plate can be removed during overhaul.