FIELD OF THE INVENTION
The present invention generally relates to leak tests in heat exchangers and pressure vessels and more particularly, the present invention relates to a method of port closure in pressure vessels to improve helium leak test procedure.
BACKGROUND OF THE INVENTION
In order to meet the reliability of manufacture, heat exchangers, pressure vessels and steam generators are subjected to leak tests. These leak tests are conducted using inert, rare and light gases such as Helium to meet the very stringent norms in order to certify the leak tightness. Normally, during the process of Helium leak testing, the ports of the heat exchanger / pressure vessel / steam generator are dummied with welded closures. After the testing, the dummies are removed by gas cutting and grinding operations which lead to more cycle time and warrant additional non-destructive examinations for welded and subsequently gas cut and ground portions. Also, thermal cycles in welding contribute for degradation of materials involved. Referring Xto the Figure-1, the ports (1) of the heat exchanger are dummied using conventional welding with a dummy plate (2).
Hence, there is a need to find out an alternate method for ports (1) closing to eliminate the above mentioned draw backs and as well as to improve the productivity.

OB3ECTS OF THE INVENTION
It is therefore, an object of the present invention is to propose a method of port closure in pressure vessels to improve helium leak test procedure.
Another object of the present invention is to propose a method of port closure in pressure vessels to improve helium leak test procedure which eliminates the dummy plate welding in the ports.
A still another object of the present invention is to propose a method of port closure in pressure vessels to improve helium leak test procedure which adapts a closure joint with facility for inter-gasket evacuation.
A further object of the present invention is to propose a method of port closure in pressure vessels to improve helium leak test procedure in which the closure joint is a flanged joint along with provision for inter-gasket evacuation.
A still further object of the present invention is to propose a method of port closure in pressure vessels to improve helium leak test procedure which uses a double / twin gasket flanged joint with inter-gasket evacuation to allow

enhanced sensitivity of pressure vacuum Helium leak testing by effectively closing the dummy ports without welding.
Another object of the present invention is to propose a method of port closure in pressure vessels to improve helium teak test procedure which is capable to establish Helium leak tightness in closure joints between higher pressure and high vacuum.
A further object of the present invention is to propose a method of port closure in pressure vessels to improve helium leak test procedure which provides pressure to vacuum closures for various sizes of ports both on straight and tapered sealing surfaces involved in closure joints.
SUMMARY OF THE INVENTION
Accordingly, a port closure arrangement has been provided for conducting pressure vacuum type Helium leak test and all the ports (1) of the heat exchanger / pressure vessel / steam generator / product (3) have been closed using the new arrangement. This methodology is shown in Figure - 2 in which a typical port (1) in the product (3) undergoing pressure vacuum Helium leak test is provided with port closure (4). For conducting this pressure vacuum Helium leak test, the product (3) with all its ports (1) closed as per the newly invented port closing arrangement (4) has to be placed inside the vacuum chamber.

During the test, high vacuum of the order of 1x10-4 mbar will be created in the vacuum chamber which accommodates the product (3) undergoing test. The inner volume of the product (3) is pressurized with 100% pure Helium up to a pressure of 10 bar (g). Prior to pressurization, the inner volume is evacuated to 1x10-4mbar in order to ensure 100% pure Helium in side the product (3).
Figure - 3 gives the details of this newly developed port closure (4).
The port closure system (4) has been constructed using twin gaskets or double gaskets (8,9) which are made up of neoprene rubber material. The inner gasket (8) which is nearer to the bore of the port (1) is partially Helium leak tight, and shows traces of Helium leakage crossing this inner gasket (8) into an inter gasket space between the inner and outer gaskets (12) during pressurisation inside the product (3). Due to this, Helium pressure build up takes place in this inter gasket space (12). If the inter gasket pressurization and rise in Helium concentration in the inter gasket space (12) are maintained at sufficiently lower levels, then only, the outer gasket (9) which is nearer to the outer side would prevent completely the flow of this inter gasket space (12) filled Helium to the high vacuum side or to the vacuum chamber (which inter alia ensures a complete leak tightness of the closures). Thus, based on the combined effect of inner gasket (8) and outer gasket (9) operations, a totally reliable and full proof Helium leak tight performance can be achieved for the newly developed port closures (4). Once the ports (1) are getting proved for effective closure with

Helium leak tightness, then only it is possible to achieve reliable Helium leak tightness verification on the product (3).
Therefore, to achieve a full proof Helium leak tightness in the port closures (4), a provision of double or twin gaskets (8, 9) is made as shown. Tightening of the nuts (11) over the studs (10) results in the compression of both the inner and outer gaskets (8, 9) in between the two circular sealing surfaces and this double sealing is desired for achieving effective Helium leak tightness. One of the sealing surface is on the closing plug (5) which serves the function of top flange in the newer design and the other sealing surface is the face or end (straight or taper) portion of the product's port (1) which is existing between the inner diameter and outer diameter of the port (1). Two gaskets' combined operation ensures an effective leak tightness of 100% pure Helium between 10 bar (g) maintained inside the product (3) and high vacuum (1x10-4mbar) maintained out side the product (in the vacuum chamber).
Further, a through hole is made on the closing plug (5) in the area in between the inner and outer gaskets (8,9) to conveniently access the inter gasket space (12) for enhancing the full proof leak tightness of the new closure system (4) by facilitating the connection of a suction tube (13) with the inter gasket space (12). This arrangement allows evacuation of the inter-gasket space (12) and Helium, if any, leaked from the inner gasket (8) into the inter gasket space (12) will be sucked out and removed and hence it will not cross the outer gasket (9) so as to enter into the vacuum chamber. By this, effective and enhanced tightness of the closure (4) between 10 bar (g) 100% pure Helium pressure and

high vacuum of 1x10-4mbar is ensured. Suction tube (13) is seal welded to the closing plug (5) top as shown.
To this suction tube (13), a vacuum pump for evacuation of inter gasket space (12) is connected during the pressure vacuum Helium leak test. Alternately, a Helium hose is connected to the suction tube for pressurizing the inter gasket space (12) with Helium. This inter gasket space (12) accessible for Helium pressurisation / evacuation further allows an independent performance testing of the inner and outer gaskets separately as a preparatory part prior to conducting a full fledged pressure vacuum Helium leak test (where the inter gasket space will be separately evacuated or pressurized). One each reaction bar ring (7) and retainer flange (6) respectively, is provided to the invented twin gasket flanged system for ensuring tightening of the closing plug (5) with the port face (1) using nuts (11) and studs (item 10) with the inner and outer gaskets (8,9) in between. According to the invention, the closing plug (5) which is a top flange of the port closure, is welded with a suction tube (13) as shown in Figure-4.
After assembling all the port closures in all the openings of the product (which is to be pressure-vacuum Helium leak tested), the performance of individual gaskets was tested initially by following the sequences as given below.
A. The inner volume of the product was first evacuated and through the inter gasket space (by means of suction tube), Helium was sent. There was no signal rise practically in a leak detector connected to the

inner volume of the product, which indicated the satisfactory performance of inner gasket in vacuum test (from inter gasket space or outer side of inner gasket to inner side of inner gasket or inner volume of product under test no Helium leak flow has taken place).
B. The inter gasket space was evacuated by connecting a vacuum pump to
the suction tube. Helium was admitted into the inner volume of the
product in small quantities, then by having the leak detector connected
to the inter gasket space, the leak tight performance of inner gasket in
vacuum test was checked. Leak free condition of inner gasket for flow
from inner side of gasket (inner part of product) to outer side of the
gasket (inter gasket space) was practically verified in this method.
C. The inner volume of the product was evacuated and then filled up with
100% pure Helium. Helium pressure was increased to about 10 bar (g).
By accessing the inter gasket space (through suction tube) with sniffer
probe connected to the leak detector, the performance of the inner gasket
for its leak tightness in pressure type Helium leak test was checked.
Leakage from inner side of inner gasket to outer side of inner gasket due
to pressurization was measured by the sniffer probe. Replacing the sniffer
probe by the vacuum cup connected to the leak detector, we measured
the global leakage from the inner side of inner gasket to the outer side of
the inner gasket in the pressure - vacuum Helium leak test condition also.
In these tests, higher leak rates exceeding the acceptance criteria for the
product was observed.
D. Similarly, by pressurizing on the inter gasket space to 10 bar (g) and
sensing for Helium inside the product, we tested for the performance of
inner gasket for its Helium leak tightness from outer side to inner side in

both pressure type and pressure- vacuum type Helium leak tests. In these tests also, higher leak rates exceeding the acceptance criteria for the product was observed.
E. By evacuating the inter gasket space to high vacuum and then spraying
Helium on outer gasket's out side (outer part of test product at port
closure location) the outer gasket's performance for leak tightness was
tested in a vacuum type test for flow from outer side of outer gasket to
its inner side (inter gasket space). In this test, satisfactory performance
was observed.
F. By pressurizing the inter gasket space to 10 bar (g) and sniffing for
Helium on outer gasket's outer side, the performance of the outer gasket
was tested for leak tightness from its inner side to outer side in pressure
tests. For this leak path, to perform pressure-vacuum test, the inter
gasket space of the product was pressurized when product was placed in
side the vacuum chamber so that the outer side of outer gasket could be
maintained in high vacuum. In these tests also, higher leak rates
exceeding the acceptance criteria for the product was observed.
G. The test product was placed inside the vacuum chamber. The inter gasket
space was given a light spray of Helium. By this, performance of the
outer gasket for leak tightness was tested in vacuum type tests for flow
from inner side of outer gasket to its outer side and this has given
satisfactory results.

The results obtained in the performance tests A to G are summarized as given in Table -1. The following important inferences are drawn.


1. Each of the gasket works well in vacuum type tests by individually rendering a leak tightness of 1x10-12 Pam3s-1 or better (practically zero leakage rate).
2. Each of the gasket allows profuse flow of Helium resulting in individual gasket's leakage rates to the extent of 1x10-5Pam3s-1 (which is higher than the acceptance criteria of 1x10-8Pam3s-1 for the product) in pressure and pressure-vacuum tests.
Based on the inferences, it was concluded that there would be leakage of inner gasket with a leak rate / flow rate exceeding the acceptance criteria during the pressurisation of product at its inner volume to 10 bar (g) (while conducting the pressure-vacuum Helium leak test by placing the 100% pure Helium pressurised product in the vacuum chamber). This continuous flow of Helium due to leakage of the inner gasket is expected to further build up of pressure in the small inter gasket volume and then this pressurised Helium from the inter gasket space is quite likely to flow crossing the outer gasket in to the vacuum chamber at a rate which would be exceeding the acceptance criteria for the product. This would ultimately result in leakage of the port closure systems to a level higher than the acceptance criteria and consequently the product's test joints (other than port closures) would not get leak tested at all.
Therefore, it was decided to have an effective and working inter gasket space evacuation in place while conducting the pressure-vacuum Helium leak test. The evacuation in this space would continue till the completion of the test for the positive, full proof and total removal of inter gasket spaces' Helium collections due to inner gaskets' leakage. This immediate and continuous Helium removal

from the inter gasket spaces ensures avoiding Helium pressure build ups in the inter gasket spaces and hence the possibility of Helium leakage flow from there to the vacuum chamber after crossing the outer gasket is totally eliminated. (If this inter gasket spaces evacuation is not done, Helium pressure build up in the inter gasket spaces due to leakage flow of pressurised Helium after crossing inner gaskets, leakage flow of thus collected Helium from inter gasket spaces after crossing outer gaskets into vacuum chamber and consequently the stage of inability to conduct pressure-vacuum Helium leak test would all become inevitable as already explained).
With this inter gasket spaces evacuation in place, a complete pressure - vacuum Helium leak test was successfully performed. During this test, pure Helium of 10 bar (g) was maintained inside the product and high vacuum of 1x10-4mbar was maintained out side the product in the vacuum chamber. The pressure-vacuum seal established by twin gaskets working in tandem along with the combined operation of inter-gasket evacuation ensured 100% leak tightness from inner side of product to vacuum chamber. The leak meter connected to the vacuum chamber did not show up any increase in its original back ground reading and it was always less than 1x10-12Pam3s-1 for 3 hours duration (the time for which observation was made). This has clearly demonstrated and proved that the port closures' effective and enhanced leak tightness by using double gaskets in combined operation mode along with inter gasket space evacuation which enables the achievement of the desired 100% leak tightness of port closures ultimately and this a mandatory requirement for conducting pressure-vacuum tests effectively.

Based on the satisfactory results obtained in the first test mentioned as above, the inventive port closures using double gaskets and inter-gasket evacuation have been introduced for pressure-vacuum Helium leak tests. To close various sized ports of both straight face / end type and taper face / end type, port closures using double gaskets and an inter gasket space along with a suction tube (to access the inter gasket space) have been made. Such closure systems in sets have been made to cover the entire range of products to close their different sized ports (port size range = 15mm to 600mm). With this new arrangement, in all the pressure-vacuum leak tests, all the port closures are ensured for complete and thorough leak tightness which facilitate conducting pressure vacuum leak tests for the product's material or other joints or both as required.
Process flow chart for conducting the pressure vacuum Helium leak test after sealing the ports using newly invented port closures is given in Figure - 7.
BRIEF DESCRIPTION OF THE ACCOMPNYING DRAWINGS
Figure - 1 shows the existing arrangement of the product's ports closing arrangement by using welded dummies.
Rgure - 2 shows the introduction of flanged joints for the ports closing replacing the welded dummies in the heat exchanger / pressure vessel / steam generator / product.
Rgure - 3 shows a typical arrangement of the newly invented port closure with all the details of sub-components involved.

Figure - 4 shows the closing plug (top flange) welded with suction tube for facilitating the inter-gasket space evacuation.
Figure - 5 shows the arrangement for inter connecting all the inter gasket spaces using connecting lines welded between all the suction tubes (of the ports) and a common suction header which has a provision for attaching a connector for leak testing purposes.
Figure - 6 shows the complete arrangement of the product's pressure - vacuum Helium leak testing by keeping the set up as shown in Figure - 5 above in side the vacuum chamber.
Figure - 7 gives the process flow for the use of the newly invented twin gasket sealed, inter gasket space evacuation enabled and flanged connection type of port closure system for carrying out pressure vacuum Helium leak tests on the product,
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION
Referring to Figure - 1:
In Figure - 1, prior art system of the port closing arrangement using welded dummies is shown. In this, a typical port (1) of the heat exchanger / pressure vessel / steam generator / product is used. To the end opening of the port (2), which is a dummy plate, is welded (by placing the dummy plate on the open end face - sealing surface - of the port) in order to ensure port closure.

Referring to Figure - 2 :
In Rgure - 2, a schematic arrangement of the newly developed port closure is shown. In this, the product (3) is a pressure vessel / heat exchanger / steam generator - which is undergoing pressure vacuum Helium leak test. There are number of ports (1) of different sizes (with straight or tapered surfaces at the sealing end surfaces). Each of the port (1) is closed with a port closure (4) which is the newly developed port closing arrangement. It is a pre-requisite to fix the port closure (4) on all the ports before starting the leak test.
Referring to Figure - 3 :
In Rgure -3, complete details of the newly developed port closing arrangement (4) are shown. This new port closure system (4) is constructed using twin gaskets or double gaskets. Here, we have an inner gasket (8) and outer gasket (9) - both are made up of neoprene rubber material. Basically, they are circular to seal circular openings of ports (1) by getting placed on end / face sealing surface. Their sizes (diameter and width) are chosen in such a way that both of them would seat on the port's sealing surface by leaving a definite radial gap in between them as shown. The inner gasket (8) is nearer to the bore of the port and will have to be Helium leak tight to contain leakage flows from the product's inner volume into the space (12) between gaskets after crossing the inner gasket.
In between the inner and outer gaskets (8, 9) there is an inter gasket space (12). This is an annular volume existing between the outer diameter of inner gasket and inner diameter of outer gasket, and the height of the volume is equal

to the thickness of the gaskets. Traces of Helium leakage, if any, will be crossing the inner gasket into inter gasket space being a space between the inner and outer gaskets (12) during pressurisation of Helium inside the product. Due to this, Helium pressure build up would take place in this inter gasket space (12). If this inter gasket space pressurization and Helium concentration rise in the inter gasket space (12) are maintained at sufficiently lower levels, then only, the outer gasket (9) which is nearer to the outer side will prevent completely the flow of inter gasket space (12) filled Helium to high vacuum side or to vacuum chamber and this is the desirable requirement of effective leak tightness from the closures. Inner side of outer gasket (9) is the inter gasket space (12) and outer side is the vacuum chamber which accommodates the product undergoing pressure vacuum Helium leak test.
Figure - 3, further shows a plurality of studs (10) and nuts (11) which are usually made up of regular fastener materials. Tightening of the nuts (11) over the studs (10) results in compression of both the inner and outer gaskets (8,9) in between the two circular sealing surfaces. One of the sealing surface is on the closing plug (5) which serves the function of top flange and the other sealing surface is the face or end (straight or taper) portion of the product's port (1) which is existing between the inner diameter and outer diameter of the port (1). Two gaskets' combined operation ensures an effective leak tightness of Helium between 10 bar (g) and high vacuum (1x10-4mbar) during the test.

Further, a through hole is made on the closing plug (5) in the area in between the inner and outer gaskets to access the inter gasket space (12) which is also part of the inter gasket space - is conveniently used for enhancing the leak tightness of the new closure system (4) by facilitating the connection of a suction tube (13) with the inter gasket space (12). Suction tube (13) is a small circular tube segment of metallic material welded to the top of the closing plug (5) at the inter gasket space access location. This arrangement will facilitate evacuation of the inter-gasket space (12) and Helium, if any, leaked from inner gasket (8) into the inter gasket space (12) will be sucked out and removed and hence it will not cross outer gasket (9) at all. By this, effective and enhanced Helium leak tightness of the new port closure system (4) between 10 bar (g) pure Helium pressure and high vacuum of 1x10-4mbar is ensured.
To the suction tube (13), a vacuum pump is connected for evacuation of inter gasket space during the pressure vacuum Helium leak test. Alternately, a Helium hose can be connected to the suction tube (13) for pressurizing the inter gasket space (12) with Helium. This inter gasket space (12) access for Helium pressurisation / evacuation will also facilitate for the independent performance testing of the inner and outer gaskets separately as parts of preparatory work prior to conducting full fledged pressure vacuum Helium leak test (in this full fledged test, inter gasket space will be separately evacuated as a mandatory requirement).

Figure - 3, still further shows one each reaction bar ring (7) and retainer flange (6) respectively and they are of metallic materials. They are essential items of the new twin gasket flanged system for ensuring the tightening of closing plug (5) with port face (1) using nuts (11) and studs (10) with inner and outer gaskets (8, 9) in between the closing plug (5) and port face (1).
Referring to Figure - 4 :
Figure - 4 gives the exclusive view of a closing plug (5) which is the top flange of the system- with suction tube (13) in welded condition.
Referring to Figure - 5 :
In Rgure - 5, the arrangement for inter connecting all the inter gasket spaces (12 of Figure-3) is shown. Using a plurality of connecting lines (14) welded between all the suction tubes (of the ports (13) and a common suction header (15) which has a provision for attaching a connector for leak testing (16), this is arranged. The connector for leak testing (16) facilitates for conducting Helium leak test of all the lines and their weld joints by connecting either an evacuation line or a pressurizing line to this connector for leak testing (16). Alternately, this connection may come out openly to atmosphere.
Referring to Rgure - 6 :
In Rgure - 6, a complete arrangement of the product's pressure - vacuum Helium leak testing by keeping the set up as shown in Rgure - 5 above in side

the vacuum chamber (17) is shown. In this, the product (3) under test is shown as placed in the vacuum chamber (17). The product (3) along with its ports (1) closed using the newly invented port closure systems (4) and connecting lines (14) welded to the respective suction tubes (13) at one end and common suction header (15) at other end is placed in the vacuum chamber (17) as shown for conducting pressure-vacuum Helium leak testing. In this Figure 6, the connector for leak testing (16) will facilitate for the evacuation of inter gasket spaces (12) through the common suction header (15) during the pressure vacuum Helium leak test or it will be kept in the 'open to atmosphere' condition in order to diffuse the inter gasket spaces' (12) Helium collections.
Referring to Figure - 7 :
Figure - 7 gives the process flow for the use of the newly invented twin gasket sealed, inter gasket space evacuation enabled and flanged connection type of port closure system for carrying out pressure vacuum Helium leak tests on the product,
Based on this invention, 'pressure-vacuum test described in leak testing hand books has been put into industrial deployment for conducting the Helium leak testing of products / heat exchangers / pressure vessels / steam generators for the first time.
According to the invention, a double gasket type port closures with inter-gasket evacuation have been put into successful use in the pressure-vacuum tests for closing the ports with openings (with Helium leak tightness between pressure and vacuum) ranging from 15mm to 600mm.

The new closures have been successfully developed for both straight and taper faces and the leak tightness results in both the categories are equally excellent.
The new closures offer advantage of quick fitting and dismantling feasibility.
The new port closures offer the best advantage of effective closing of all the openings of the product without resorting to welded end covers. Therefore, the material is not getting affected due to heat effects of welding of covers. Cutting allowance for welded covers is not required and finished part itself can be used directly.
The sensitivity of Helium leak test is enhanced in the pressure-vacuum test based on adoption of new port closures and this is possible with the use of 100% pure Helium maintained at higher pressure gradients (11 bar) for conducting the test.
The following are the unique features of the inventive port closures in a pressure vacuum test.
 100% pure concentration Helium is used in this method compared to the
best concentration levels of 70-80% achieved in vacuum tests.
 Pressure gradient involved here is 11 times compared to vacuum test and
hence sensitivity of test is enhanced.
100% pure concentration Helium is used in this method compared to the best concentration levels of 50% achieved in pressure tests.
 Pressure gradient involved here is 11 times compared to normal pressure
test and hence sensitivity of test is enhanced.

 Pressure method senses only sample Helium where as 100% leaking Helium is sensed and quantified by pressure-vacuum method
The following are the steps involved in a method of port closure (using the new closures) in pressure vessels to improve helium leak test procedure:
placing respective retainer flanges (6) concentrically on all the ports (1) of the pressure vessel (3);.
locating the respective reaction bar rings (7) concentrically on the ports of the product (3);
positioning the respective inner gaskets (8) and outer gaskets (9) concentrically on the sealing faces of the ports (1) leaving a gap between both the gaskets radially for accommodating an inter gasket accesses;
parallely, carrying out fillet / Seal welding of respective suction tubes (13) to closing plugs (5) at their inter gasket space access holes (12);
positioning each of the closing plugs (5) concentrically over the respective twin gaskets (8 and 9) in such a way that the inter gasket spaces (12) of the closing plugs (5) along with corresponding suction tubes (13) come in between the pair of respective two gaskets within the radial spaces between the gaskets;
fixing studs (10) into the holes of the respective closing plugs (5) and placing corresponding nuts (11) over the studs (10) and tightening the same, allowing compression of the corresponding gaskets (8,9) which close all the ports (1);

evacuating the inter gasket spaces (12) individually one by one using the corresponding suction tubes (13) and ensuring the Helium leak
tightness of the outer gaskets (9) by Helium spray on the outer part of port closures (4) in vacuum type tests against a desired leak tightness of 1x10-12Pam3s-1 or better;
- evacuating inter gasket spaces (12) individually one by one using the corresponding suction tubes (13) and ensuring the leak tightness of inner gaskets (8) by admitting 10% concentrated Helium into the inner volume of the product (3) in vacuum type tests against the desired leak tightness of 1x10-12Pam3S-1 or better;
pressurizing the inner volume of the product (3) using the Helium gas up to 10 bar (g) and evacuating, the inter gasket spaces (12) one by one including recording of the readings of a leak detector connected to the inter gasket spaces (12) through the corresponding suction tubes (13)
This pressure-vacuum test demonstrates the extent of leak tightness of the respective inner gaskets (8) one by one. The desired level of maximum allowable leak rates of 1x10-5Pam3s-1 or better is ensured for each of the individual spaces (12) in this testing ;
After conducting separately confirmatory tests for inner and outer gaskets
(8,9) of individual ports (1), connecting all the inter gasket spaces (12) together by providing welded connecting lines (14) to the individual suction tubes (13) such that the other ends of the individual connecting lines (14) are welded to a common suction header (15) which has got one more connection called connector for leak testing (16) in order to facilitate for conducting Helium leak test of all the lines and their weld joints by

connecting either an evacuation line or a pressurizing line to this connector for leak testing. Alternately, this connection may come out openly to atmosphere ;
connecting the volumes of the common header (15), all connecting lines (14), all suction tubes (13) and the inter gasket spaces (12) in a combined manner through the connector for leak testing (16); and evacuating the combined entire volume by connecting a vacuum pump; connecting a mass spectro meter leak detector through a valve parallel to vacuum pump;
- isolating the vaccum pump and spraying Helium on all the connecting lines
(14) to the common header (15) joints, connecting lines (14) to suction
tubes (13) joints and connector for leak testing (16) to common header (15)
joint and ensuring the leak tightness of these joints against 1x10-12Pam3s-1 or
better;
- evacuating to 1x10-4 mbar or better the entire inner volume of the
product (3) undergoing pressure vacuum Helium test and then pressurizing
100% pure Helium into the inner volume of the product (3) to a pressure of
10 bar (g); through the connector for leak testing (16), evacuating the
combined volume of inter gasket spaces (12), the suction tubes ( 13), the
connecting lines (14) and the common suction header (15) to a vacuum level
of 1x10-4 mbar or better and isolation of the pump;
- connecting the leak detector in the line parallel to the vacuum pump through
a valve arrangement and determining the cumulative leakage of all the inner

gaskets (8) due to the flow of leaking Helium through all the inner gaskets (8) into the common suction header (15) after passing through inter gasket space (12), suction tubes (13) and connecting lines (14) and this rate has been in the range of 1x10-5Pam3s-1 or better;
EXAMPLE
After the confirmation of closure's successful performance, and before going in for pressure-vacuum test, first the leak tightness of the product's (3) test joints (welds, assembly joints and materials) have been first checked in the regular vacuum type test and pressure type test separately. These confirmatory vacuum type and pressure type tests have been done as parts of regular testing sequence for the product (3) before placing the product (3) inside the vacuum chamber (17) as shown in Figure-6, considering the fact that there would be no access for product's joints during the pressure-vacuum test.
Figure - 6 shows the details of actual pressure vacuum Helium leak testing. In this, the product (3) under test is first placed in the vacuum chamber (17) as shown. The product's (3) port closure systems (4) and vacuum chamber (17) together are made up of 3 spaces. All the three spaces are accessible for pressurization or evacuation from out side. The details about these 3 SPACES are given below.
 SPACE 1 is a high vacuum space of the vacuum chamber (17) with a vacuum level of 1x10-4 mbar or better during the actual pressure-vacuum test; wherein

 SPACE 2 is a combination of all inter r gasket spaces (12) of port
closures (4), suction tubes (13) common suction header (15) and
connecting lines (14), the space being normally at atmospheric
pressure or it can be evacuated using a connector (16) for leak testing;
and wherein
SPACE 3 is the inner volume of the product (3) under pressure-vacuum Helium leak test, which can be evacuated to 1x10-4 mbar or better and then pressurized with 100% pure Helium to 10 bar (g),
In addition to the above three spaces, a provision to connect standard Helium leak calibrator to the vacuum chamber (17) for performing system sensitivity check is provided including a provision to connect the Helium leak detector parallel to the evacuation line of the vacuum chamber (17) through a valve arrangement which allow conducting of Quantitative Helium leak test of the product (3). Leak rate observed in this test on the leak detector will be the total leakage of Helium from inner part of the product (3) which is pressurized with 100% pure Helium at 10 bar (g) to the outer part of the product which is vacuum chamber (17). As all the port closures (4) have been certified for their leak tight performance based on many confirmatory tests as explained already, if any leakage observation is noticed in the leak detector, then it is due to leaks in the product (3) joints only.

The systematic STEPS in the actual pressure vacuum Helium leak test are given below.
- evacuating of SPACE 1 of vacuum chamber (17) to a vacuum level of 1 x10-4 mbar or better after placing a heat exchanger (3) in the vacuum chamber (17).
- separately evacuating SPACE 2 continuously till the completion of the test for full proof and total removal of helium gas collected in the inter gasket spaces (12) due to leakage in the inner gaskets (8);

- conducting vacuum hold test for 1 hour for SPACE1 by isolating the vacuum pumps connected to this space; and determining sensitivity of the leak detector connected parallel to the evacuating line through valve arrangement;
- determining vacuum system's sensitivity for SPACE 1 by admitting Helium from a standard leak calibrator connected to the vacuum chamber (17),
- closing the calibrator and evacuating SPACE 1 to remove the Helium entered during the system sensitivity check till the attainment of a leak meter reading of 1x10-12 Pam3s-1 or better in the said leak detector which is connected parallel to vacuum pump, and isolating the pump for carrying out pressure vacuum Helium leak testing;

evacuating the product (3) to a vacuum level of 1x10-4 mbar or better and injecting 100% Helium into this SPACE 3 to a positive pressure of 10 bar (g), and recording the meter readings on the leak detector connected to said SPACE 1 wherein an increase in the value on leak meter in respect of the value before pressurization of Helium is determined to be the global leakage rate due to leakage from the inner part of product (3) to the outer part (17) in this pressure-vacuum Helium leak test. As we have positively ensured the fool proof leak tightness of all the port closures (4) using the innovatively made double gasket systems with the facility for inter gasket evacuation, the leak meter reading with an increasing trend (from its back ground) is due to the leakage from product's (3) joints and material undergoing test only.
Thus, using the new port closures (4), the product / heat exchanger / pressure vessel / steam generator (3) has been successfully pressurevacuum Helium leak tested in a global manner for the determination of total leakage rate of all the test joints.
The draw backs mentioned in the lBack ground of the Invention' with the welded dummies have been eliminated based on using the newly invented port closures and this results in substantial savings in cycle time of the product by rendering productivity improvement in leak testing. Novel method of conducting pressure-vacuum Helium leak testing to achieve the desired

higher test sensitivities has been made possible based on this invention. Also, elimination of welded dummies renders material savings by avoiding additional allowances otherwise required exclusively for facilitating the test.
This also helps for preserving the original mechanical properties of materials (especially this is relevant for critical materials) by avoiding 'heat cycles' (while welding of dummies before test and gas cutting of dummies after test) which are inevitable with earlier version of welded dummies for ports. Also, non destructive tests for welding and cutting of dummies have been eliminated.

WE CLAIM :
1. A new method of port closures in pressure vessels to improve helium leak test procedure, comprising the steps of:
placing respective retainer flanges (6) concentrically on all the ports (1) of the pressure vessel (3);.
locating the respective reaction bar rings (7) concentrically on the ports (3);
positioning the respective inner gaskets (8) and outer gaskets (9) concentrically on the sealing faces of the ports (i) (leaving a gap between both the gaskets radially for accommodating an inter gasket accesses);
parallely, carrying out fillet / Seal welding of respective suction tubes (13) to closing plugs (5) at their inter gasket space access holes (12);
positioning each of the closing plugs (5) concentrically over the respective twin gaskets (8 ,9) in such a way that the inter gasket spaces (12) of the closing plugs (5) along with corresponding suction tubes (13) come in between the pair of respective two gaskets within the radial spaces between the gaskets;
fixing studs (10) into the holes of the respective closing plugs (5) and placing corresponding nuts (11) over the studs (10) and tightening the same, allowing compression of the corresponding gaskets ( 8 ,9) to achieve closing of all the ports (1);

evacuating the inter gasket spaces (12) individually one by one using the corresponding suction tubes (13) and ensuring the Helium leak tightness of the outer gaskets (9) by Helium spray on the outer part of port closures (4) against a the desired leak tightness of 1x10-12Pam3s; or better;
evacuating inter gasket spaces (12) individually one by one using the corresponding suction tubes (13) and ensuring the leak tightness of inner gaskets (8) by admitting 10% concentrated Helium into the inner volume of the product (3) in vacuum type tests against the desired leak tightness of 1x10-12Pam3s-1 or better;
pressurizing the inner volume of the product (3) using the Helium gas up to 10 bar (g) and evacuating the inter gasket spaces (12) one by one including recording of the readings of a leak detector connected to the inter gasket spaces (12) through the corresponding suction tubes (13); this pressure-vacuum test demonstrates the extent of leak tightness of the respective inner gaskets (8) one by one. The desired level of maximum allowable leak rates of 1x10-5Pam3s-1 or better is ensured for each of the individual spaces (12) in this testing ;
after conducting separately confirmatory tests for inner and outer gaskets (8, 9) of individual ports (1), connecting all the inter gasket spaces (12) together by providing welded connecting lines (14) to the individual suction tubes (13) such that the other ends of the individual connecting lines (14) are welded to a common suction header (15) which has got one more connection called

connector for leak testing (16) in order to facilitate for conducting Helium leak ' test of all the lines and their weld joints by connecting either an evacuation line or a pressurizing line to this connector for leak testing, alternately, this connection may come out openly to atmosphere ;
connecting the volumes of the common header (15), all connecting lines ( 14), all suction tubes (13) and the inter gasket spaces (12) in a combined manner through the connector for leak testing (16); and evacuating the combined entire volume by connecting a vacuum pump;
connecting a mass spectra meter leak detector through a valve parallel to the vacuum pump;
isolating the vacuum pump and spraying Helium on all the connecting lines (14) to the common header (15) joints, connecting lines (14) to suction tubes (13) joints and connector for leak testing (16) to common header (15) joint and ensuring the leak tightness of these joints against 1x10-12Pam3s-1 or better;
evacuating to 1x10-4 mbar or better the entire inner volume of the product (3) undergoing pressure vacuum Helium test and then pressurizing 100% pure Helium into the inner volume of the product (3) to a pressure of 10 bar (g) and through the connector for leak testing (16), evacuating the combined volume of the inter gasket spaces (12), the suction tubes ( 13), the connecting lines (14) and the common suction header (15) to a vacuum level of 1x10-4 mbar or better and isolation of the pump; and

connecting the leak detector in a line parallel to the vacuum pump through a valve arrangement and determining the cumulative leakage of all the inner gaskets (8) due to the flow of leaking Helium through all the inner gaskets (8) into the common suction header (15) after passing through inter gasket space (12), suction tubes (13) and connecting lines (14) and this rate has been in the range of 1x10-5pam3s-1 or better.
2. A new method of port closures in pressure vessels to improve helium leak
test procedure based on preparatory steps given above and the performance of actual tests comprising the steps of:
- evacuating SPACE 1 of a vacuum chamber (17) to a vacuum level of 1 x 10-4mbar or better after placing a heat exchanger (3) in the vacuum chamber (17);
- separately evacuating SPACE 2 (which is the combination of all inter gasket spaces (12) of port closures (4), suction tubes (13) common suction header (15) and connecting lines (14), this space will be normally at atmospheric pressure or it can be evacuated using connector for leak testing (16) continuously till the completion of the test for full proof and total removal of helium gas collected in the inter gasket spaces (12) due to leakage in the inner gaskets (8);

conducting vacuum hold test for 1 about hour for SPACE 1 by isolating the vacuum pumps connected to this space ; and determining sensitivity of the leak detector connected parallel to the evacuating line through valve arrangement;
- determining vacuum system's sensitivity for SPACE 1 by admitting Helium from a standard leak calibrator connected to the vacuum chamber (17) - for SPACE 1 ;
- closing the calibrator and evacuating SPACE 1 to remove the Helium entered during the system sensitivity check till the attainment of a leak meter reading of 1x10-12 Pam3s-1 or better in the said leak detector which is connected parallel to vacuum pump and isolating the pump for carrying out pressure vacuum Helium leak testing; and
evacuating the product (3) to a vacuum level of1x10-4 mbar or better and injecting 100% Helium into this SPACE 3 to a positive pressure of 10 bar (g), and recording the meter readings on the leak detector connected to said SPACE 1 wherein an increase in the value on leak meter in respect of the value before pressurization of Helium is determined to be the global leakage rate due to leakage from the inner part of product (3) to the outer part (17) in this pressure-vacuum Helium leak test; as we have positively ensured the fool proof leak tightness of all the port closures (4)

using the innovatively made double gasket systems with the facility for inter gasket evacuation, the leak meter reading with an increasing trend (from its back ground) is due to the leakage from product's (3) joints and material undergoing test only; where in
SPACE 1 is a high vacuum space of the vacuum chamber (17) with a vacuum level of 1x10-4 mbar or better during the actual pressure-vacuum test; wherein
SPACE 2 is a combination of all inter gasket spaces (12) of port closures (4), suction tubes (13) common suction header (15) and connecting lines (14), the space being normally at atmospheric pressure or it can be evacuated using a connector (16) for leak testing; and wherein
SPACE 3 is the inner volume of the product (3) under pressure-vacuum Helium leak test, which can be evacuated to 1x10-4 mbar or better and then pressurized with 100% pure Helium to 10 bar (g).