The present invention concerns a boiler tube position retainer assembly for stabilizing and supporting boiler tubes in boilers. The present invention more particularly concerns boiler tube clips for use in large industrial boilers. Primary or secondary furnace superheaters and reheaters function as important industrial power sources throughout the world. Power boilers, which may be one hundred feet in width or more with boiler tubes of over forty feet in length, are used as industrial power generators in various applications. For example, industrial power boilers may be used as steam generators in paper mills or power plants.
Similar to a smoke stack, superheated gases enter through one end of a furnace and exit through the other end. Metal boiler tubes are positioned across the flow of heated gas to maximize the heat transfer to the metal tubes. Boiler tubes are spaced apart to allow gas to flow around the metal boiler tubes. Although these metal boiler tubes are positioned to maximize heat transfer, debris may get caught between the boiler tubes if they are spaced too close together. If boiler tubes are positioned too far apart, heat transfer may not be maximized.
When water is pumped through the boiler tubes, the boiler becomes a powerful steam generator. Water entering into the boiler tube at one end may quickly heat to become superheated steam of over nine hundred degrees Fahrenheit.
Once the boiler tubes are positioned as desired, they are stabilized and kept in place by tube clips or boiler tube assemblies. Such assemblies also structurally support the boiler tubes during operation of the heaters. Previously, boiler tubes clips and assemblies were often welded directly onto the boiler tubes. One piece of the clip may be welded to the boiler tube directly, while another piece of the clip may be welded directly to the adjacent tube.
As seen in an example of a prior art assembly in
When the two pieces of this assembly are properly positioned, there is very little tolerance for expansion and contraction of the boiler tubes, thereby placing stress on the tubes at the weld connection. When the stress is too great, the boiler tubes will break, rupture or leak, causing leakage and eventual shut down of the boiler for an unscheduled repair. The clip is generally stronger than the boiler tubing, and therefore tube failure occurs before clip failure in most cases.
Another example of boiler tube assemblies or clips 22 and 24 are seen in
In the prior art, such welds penetrate through the boiler tubes and introduce weak points as the boiler tubes and clips expand and contract during normal operation of the furnace. Superheating causes stress and contributes to instability. Because these pressure part attachments do not adequately allow for expansion and contraction, or for allowances and movement caused by vibrations due to movement of gases and soot, such attachments often fail. In addition, because such clip assemblies are often made of cast iron material, which are stronger than the boiler tubes, failure often occurs at the weld points of the boiler tubes. Failure at such points will lead to boiler tubes rupturing or leaking.
When the boiler tubes fail, steam leaks cause the stoppage of the power boilers. Loss of productivity ensues until the entire tube assembly is examined and the leakage is identified and corrected. Each weld connection must often be examined by licensed professionals and corrected to industry standards. Specialized inspectors and welders are needed for boiler code inspection. Such failures cost boiler operators loss of productivity and increased expenses.
The present invention concerns a saddle clip styled, boiler tube position retainer assembly for securing boiler tubes in power boilers. The present invention supports and stabilizes the boiler tubes while allowing for slight vertical and horizontal movements. The present invention also concerns a method for positioning and stabilizing boiler tubes in power boilers, while allowing for some vertical and horizontal movement during expansion and contraction without damage to tube sheet or boiler tubes.
The tube assembly device of the present invention maintains spacing for proper heat transfer and avoids tubing wall removal should weld failure occur, thereby decreasing leakage of boiler tubes, shut down time and unscheduled down time for inspections and repairs. Productivity of the boilers is increased and maintenance costs are decreased. In the event of excess stress on the positioning assembly, the boiler tube position retainer assembly of the present invention allows for failure points to occur on the boiler tube position retainer assemblies rather than on the boiler tubes themselves.
Furthermore, fewer procedures are required to assemble the boiler tube position retainer assembly of the present invention, i.e., two vertical welds per attached saddle components, male and female. If failure is imminent, the clip is designed to fail prior to damaging the pressurized tubes. Using the present invention, less welding steps and procedures are involved and results in a simpler device. Overall, the assembly of the present invention is more cost effective, and less boiler tube failure results in fewer shut downs and decreased cost of repairs.
The tube attachment pads 54 and 56 are saddled to the boiler tubes 50 and 52. They are attached by welding along the contact surface of the saddle clip portions 60 and 62 of the tube attachment pads 54 and 56 and the boiler tubes 50 and 52. Such welds are preferably vertical fillet welds, instead of full penetrations welds of the prior art.
Also, the saddle clip portions 60 and 62 have thinner walls than the boiler tubes 50 and 52. Thus, in the event of stress or breakage, failure occurs preferably by tearing of one or more of the pad ear portions 64, 65 or 67 from the saddle clip portions 60 and 62 without damage to the boiler tubes 50 and 52. Thus, the present invention allows for a much more convenient correction mechanism that saves cost and time and increases productivity. Unlike prior art assemblies that require welds that penetrate through the boiler tubes or have clip assemblies that are stronger than the boiler tubes themselves, the current invention allows for failure to occur at the clip assembly itself, which can easily be replaced instead of repairing the boiler tubes themselves.
Preferably, the tube attachment pads are each formed as a one-piece item comprising a pad ear portion or pad ear portions and a saddle clip portion. Thus, tube attachment pad 54 comprises saddle clip portion 60 and pad ear portion 64, and tube attachment pad comprises saddle clip portion 62 and pad ear portions 65 and 67.
Each pad ear contains an alignment hole. For example, pad ear 65 has an alignment hole 68, which is drilled perpendicular to the plane of the pad ear portion 65 to form an alignment hole 68. Alignment holes for pad ears 64 and 67 are not shown in
The retaining pin 67 need not necessarily be made of code material. The retaining pin 67 maintains the spacing between the boiler tubes 50 and 52 by keeping tube attachments pads 54 and 56 at relatively fixed distances. Because the retaining pin 67 is not welded, the boiler tube position retainer assembly 48 of the present invention allows for some vertical and horizontal movement of the boiler tubes 50 and 52. Such movement may occur during start up and operation of these super boilers and allows for expansion and contraction during high temperature fluctuations.
Examining
The present invention is further advantageous in that special quantities and differing dimensional characteristics may be easily fabricated. For example, when large quantities are required, the boiler tube position retainer assemblies of the present invention may be may be easily manufactured using code approved castings.
CROSS REFERENCE TO RELATED APPLICATION This patent application is the utility application of the previously filed U.S. Provisional Applications Number 60/594,691, entitled “Boiler Tube Position Retainer Assembly” filed on Apr. 28, 2005. The Provisional Application is incorporated herein by reference.
Number | Date | Country | |
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60594691 | Apr 2005 | US |