Metal working – Method of mechanical manufacture – Heat exchanger or boiler making
Reexamination Certificate
2000-03-10
2001-09-18
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Heat exchanger or boiler making
C029S890043, C029S890054, C165S173000
Reexamination Certificate
active
06289585
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to pipe structures, and in particular to a method of attaching pipes.
2. Background of the Invention
Myriad useful structures currently in use require the mutual attachment of pipes. In the area of environmental control alone examples include radiator tubes attached to header pipes, air conditioning coils, and heat exchanger coils. In the area of power generation, one application where a plurality of tubes must be attached to header pipes is in Heat Recovery Steam Generators (“HRSG”). A typical HRSG is illustrated in FIG.
1
.
Referring now to
FIG. 1
, HRSG 2 comprises a plurality of finned tubes
6
(in the interest of clarity, the individual fins are not shown), each attached at one end to first header
4
, and an opposite end to second header
5
. An interior of first header
4
communicates with an interior of second header
5
by means of finned tubes
6
. An exterior of finned tubes
6
is surrounded by a heating medium.
In use, water enters first header
4
as indicated by arrows
8
. The water then travels to second header
5
by means of finned tubes
6
. While transiting finned tubes
6
the water is heated, and exits second header
5
as steam, as indicated by arrow
10
.
EXISTING METHODS
An existing method of attachment of two pipes is illustrated in FIG.
2
. For the purposes of this illustration, the attachment of a finned tube
6
to second header
5
is illustrated. First a bore
12
is drilled into second header
5
sized to admit finned tube
6
. Then weld prep
14
is machined into hole
12
. One extreme of finned tube
6
is then inserted into hole
12
, and weld
16
is made at the intersection of finned tube
6
and weld prep
14
. Finally, weld
16
is inspected.
A number of problems exist associated with this existing method of attaching finned tubes
6
to second header
5
. One problem is that automatic welding cannot be employed, because of interference with finned tubes
6
adjacent to the finned tube
6
being welded. The conventional method described above permits a worker to perform only approximately thirty four (34) welds every twelve hours. Given that automatic welding permits five (5) or more welds to be made simultaneously, a substantial time penalty is incurred by using manual welding, as opposed to the automatic welding as taught by the instant method.
Another problem is the lack of 100% penetration achievable using the current manual welding technique. If automatic welding were performed, power could be programmed to vary automatically with weld prep depth, in order to achieve 100% weld penetration.
Still another problem associated with the current weld method illustrated in
FIG. 2
is the difficulty inherent in welding closely spaced finned tubes
6
to a header. In the application discussed above, finned tubes
6
are typically only 5-6 inches apart. Naturally, this causes clearance problems between the welder's torch and the finned tubes
6
adjacent the finned tube
6
being welded.
Yet another problem associated with the current method is the difficulty of performing a thorough inspection: only the exterior of the header may be inspected. Thus, deficiencies that may be visible from the inside of the header pass undetected.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method of attaching pipes which permits automatic welding to be employed in pipe to pipe attachments. Design steps allowing this object to be accomplished include longitudinally dividing a header into two parts, making header bores into one header part, inserting a tube into each header bore, and automatically welding each tube into its respective header bore from the inside of the header part by means of automatic welding. Advantages associated with the accomplishment of this object is time savings, and consequent cost savings.
It is another object of the present invention to provide a method of attaching pipes which permits both inside and outside inspection of a pipe to pipe attachments. Design steps allowing this object to be accomplished include longitudinally dividing a header into two parts, making header bores into one header part, inserting a tube into each header bore, and attaching each tube to the header part. Benefits associated with the accomplishment of this object include a more thorough inspection, and less sub-specification attachments.
It is still another object of this invention to provide a method of attaching pipes which provides 100% penetration in the attachment weld. Design steps enabling the accomplishment of this object include varying the welding power to compensate for varying weld prep depth while automatically welding tube(s) to a header. An advantage associated with the realization of this object is a higher quality pipe to pipe attachment.
It is yet another object of the present invention to provide a method of attaching pipes which permits both an interior and an exterior weld. Design steps allowing this object to be accomplished include longitudinally dividing a header into two parts, making header bores into one header part, inserting a tube into each header bore, automatically welding each tube into its respective header bore from the inside of the header part by means of automatic welding, and finally making a weld exterior to the header. A benefit associated with the accomplishment of this object is a stronger, higher quality weld to attach two pipes.
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patent: 5944096 (1999-08-01), Hubert
Hughes S. Thomas
Jimenez Marc
Rooy Paul S.
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