Abstract:
A hydraulically installed tube plug with or without O.D surface enhancements and plug installation tooling, high pressure fluid system and method. The invention stops leaks in tubes with a plug that utilizes controlled high pressure fluid within the plug itself to radially expand the plug in place. Other plugs and plugging systems rely on mechanical methods for setting the plugs in the tubes with little or no control on the radial pressure applied to the tube. This lack of radial pressure control can result in a tubesheet ligament being over stressed (plastically deformed) or not enough pressure applied to stop the leak. The plug high pressure expansion tooling is designed with built in safety components that allow high pressure hydraulic expansion methods to be used safely in blind holes. The high pressure fluid system&#39;s design allows it to be used in hazardous environments.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This non-provisional patent application claims priority to the provisional patent application having Ser. No. 61/396,978, having filing date Jun. 4, 2010. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to means for hydraulically installing a tube plug within transfer tubes that are found in boilers, condensers, and other type heat exchangers, and relates to plug installation techniques, and their system and method. 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to tube plugs and plug installation techniques and more particularly to thimble type plugs and the use of high pressure expansion mandrel plug installation tooling and technique to stop leaks in tubes found in boilers, condensers and other shell-and-tube type heat exchangers. 
     Some types of tube plugs used are tapered fiber (wooden or composite material) type plugs, one piece tapered metal plugs, two-piece metal tapered pin and collar plugs, multi-piece breakaway plugs, explosive plugs and thimble plugs. The tapered fiber plugs are usually limited to low pressure and temporary applications and in many cases are not compatible with the medium that would come in contact with the plug. Tapered metal one piece and two-piece (pin and collar) type plugs rely on mechanical methods for setting the plugs in the tubes with little or no control on the radial pressure applied to the tube. They are typically installed using a hammer type device. There is no way to reliably control and measure the radial force that these type plugs exert on the ID of the tube and the surrounding tubesheet ligaments during installation. This lack of radial pressure control can result in a tubesheet ligament being over stressed (plastically deformed) or not enough pressure applied to stop the leak. These forces can vary greatly from plug to plug even when installed by the same person using the same installation tools and techniques. One plug can be too loose and leak or even fall out, while the next plug can be too tight and cause permanent ligament damage which can generate leaks in the surrounding tube-to-tubesheet joints. Other potential problems with tapered metal plugs are described in Stanley Yokell&#39;s book “A Working Guide to Shell-and-Tube Heat Exchangers”. It states Quote: “they create a crevice behind the contact surface between the plug and tube, which can lead to crevice corrosion; and the tensile stresses they generate in the tubesheet may sensitize it to stress corrosion cracking.” A disadvantage of the two-piece tapered plug is that it requires a tight friction fit in three areas to work properly. One is between the tapered pin (inner piece) and the ring (outer piece), second is between the OD of the ring and the ID of the tube and last is the surface between the tube OD and the tubesheet hole. Another disadvantage is the outer ring needs to have an initial clearance gap between it and the tube ID for the plug to be inserted. This requires a substantial deformation of the ring to engage the tube ID with sufficient force to create the interfacial pressure needed to hold it in place and seal the leak. It is possible that because the shoulder of the ring rests against the tube end during installation that the driving force necessary to seat the plug and expand it may cause the tube itself to be dislodged from its seat and create another leak path. Multi-piece breakaway plugs have a very small effective expansion range and therefore must be precisely sized to work properly: A common problem is when an undersized plug is selected for use. During installation the breakaway plugs become rapidly work-hardened during the expansion process. The resistance and resulting friction forces will cause the breakaway of the plug parts to take place before the necessary radial forces are reached that should hold the plug in place and seal the leak. The results are plugs that may loosen and fail during the operation of the unit. 
     Explosive friction fit plugs must be installed by explosive certified personnel and cannot be used in many applications because of the hazardous environments that the vessels are located in such as chemical plants and refineries. Even if they can be used, it may require whole areas of the plant to be shut down and personnel removed from the area for safety reasons during their use. Another down side of explosive plugs is the extensive cleanup required to remove the explosive residue from the vessel to prevent plant systems contamination prior to bringing the vessel back online. 
     Thimble type plugs are typically a one piece plug that resembles a thin tube with a closed end or “blind hole.” When installed using mechanical rollers the plug must fit snuggly in the tube hole to begin with to prevent it from spinning during the initial rolling process. In all of the applications discussed with the exception of explosive plugs it has been proven that when the ID of the tube hole being plugged is even slightly oval shaped it is difficult to get the plug OD to conform to the tube ID and provide a reliable sealing surface. 
     In the patent to Russell D. Wasson and David A Vossbrinck, U.S. Pat. No. 5,901,594, issued on May 11, 1999, for High Pressure Expansion Mandrel with Cams Engaging Oppositely Directed Ends of an Expandable Segmented Ring, there is disclosed a high pressure mandrel for joining a metal tube to a wall of a metal sheet surrounding an annular bore of the metal sheet. Spaced O-rings are disposed on a shaft of a mandrel that is disposed axially in the metal tube. Outboard of the O-rings, backup rings are respectively disposed on the shaft. Outboard of the backup rings are disposed segmented ring assemblies which are also disposed on the shaft. Facing opposite ends of each segmented ring assemblies are cam rings. The cam rings are disposed on the shaft. High pressure fluid by means of a conduit in the mandrel shaft provides pressure to the inner wall of the metal tube to expand the tube radially outward. Simultaneously, the high pressure fluid urges the O-rings outward toward the associated backup rings and in turn the backup rings are urged outwardly toward the associated segmented ring assemblies, respectively. Facing each of the segmented ring assemblies are cam rings. Each set of cam rings expand radially its associated segmented ring assembly in response to the high pressure fluid. 
     SUMMARY OF THE INVENTION 
     This invention contemplates the construction of a precision hollow metal plug, and its method of installation within the tube of a high pressure boiler, condenser, or other heat exchangers, in order to close off a particular tube which due to corrosive or other effects, may be subject to leaking. The precision hollow metal plug of this invention is made with a smooth blind hole formed internally, and on its external surface, incorporates a series of concentric ridges and grooves which in combination with its plug, is inserted into the tube to be plugged. A mandrel assembly with seals on both ends, and an internal passage to allow high pressure fluid, such as water or oil, to pass through it, is inserted into the plug. High pressure fluid from a pumping system is injected through the mandrel and into the area between the mandrel and its seals. The pressurized fluid, which may be subject to pressures in arrange of 20,000 psi to 60,000 psi is conducted to and is contained between the seals, and is biased against the internal surface of the plug, which forces the plug to expand radially under such pressures and causes the outer surface of the plug to come in contact with the inner surface of the tube, to create a fluidic seal. When the high pressure fluid used to expand the plug into place is relieved, by venting, it leaves a tight interfacial fit between the OD of the tube plug, and the ID of the tube that is being sealed. 
     It is, therefore, the principal object of this invention to provide a plug, having unique characteristics that provides for its pressure fitting against various tubes found in boilers and condensers, and which can be plugged in place through the application of very high psi to form a seal for a tube that is experiencing leakage, fracture, or other deterioration. 
     Another object of the present invention is an engineered thimble type tube plug made of but not limited to the following materials: high strength steel, stainless steel, brass, titanium, and other highly engineered composite materials, that can be expanded using high pressure hydro-expansion tooling and techniques. 
     Another feature of the present invention is a variation of a thimble type tube plug with a shoulder or collar that is an integral part of the plug OD used to seat the plug at the very end of a tube or annular bore in a metal sheet i.e. tube-sheet and expanded in place using high pressure hydro-expansion tooling and techniques. 
     A feature of the present invention is a variation of a thimble type tube plug with a consistent OD that will allow the plug to be positioned anywhere along the interior length of a tube or annular bore in a metal sheet i.e. tube-sheet and expanded in place using high pressure hydro-expansion tooling and techniques. 
     A feature of the present invention is a variation of a thimble type tube plug with concentric ridges as an integral part of the plug OD. These ridges facilitate the plugs ability to penetrate thin layers of scale and bite into the ID of the bore or tube surface that the plug is being expanded into and provide a more complete seal. 
     Another object of the present invention is a high pressure expansion mandrel assembly for hydro-expansion of thimble type tube plug that utilizes a pressurized medium such as but not limited to distilled water. This high pressure medium the expansion mandrel uses is supplied by an adjustable high pressure supply system that produces variable and controllable pressures between 20,000 psi and 60,000 psi. These high pressure supply systems may be engineered to utilize pneumatic controlled logic or electronic and digital control logic or a combination of both. 
     A feature of the present invention is a high press expansion mandrel that incorporates an axial passageway in the body of the mandrel that provides for a safe relief of pressure when the mandrel assembly is used in blind holes such as a thimble type tube plug. This passage normally acts as a vent hole when inserting or extracting the mandrel and prevents a hydraulic lock from taking place in the blind hole area behind the mandrel. Under conditions that might cause an undesirable buildup of high pressure in the blind-hole area behind the mandrel assembly, this passageway acts as an overpressure safety vent and prevents the area from pressurizing. 
     Another object of the present invention is a high pressure expansion mandrel that has a short raised step at one end that acts as a stop and retains various sliding parts on the mandrel when the parts are under an axial force. The opposite end of the mandrel is threaded to accept a nut that when engaged, acts to stop and retain various sliding parts on the mandrel when the parts are under an axial force in the opposite direction. 
     A feature of the present invention is a high pressure expansion mandrel that incorporates a cam surface as an integral part of the short raised step on the end of the mandrel shaft body. This integrated cam surface mates up with one side of a segmented ring assembly disposed on the mandrel shaft and works with a sliding cam ring disposed on the same mandrel shaft on the opposite side of the same segmented ring assembly. In response to high pressure being applied to the sliding cam ring, pressure is applied to the sliding segmented ring which moves in an axial direction up against the fixed integral cam surface. The forces created by the opposing cam surfaces act on the segmented ring assembly cause it to expand radially, until it comes in contact with the plug or tube inner surface. The resulting forces facilitate centering and maintaining alignment of the mandrel assembly in the axial bore. 
     Another feature of the present invention is a high pressure expansion mandrel which incorporates removable center land area (spacer) to facilitate removal and replacement of worn parts on the mandrel from the primary (threaded end) of the mandrel shaft. This spacer when in place helps locate and position the sealing components of the expansion mandrel assembly which define the expansion zone area. 
     Another object of the present invention is a high pressure fluid supply system to provide fluid under high pressure to hydraulically radially expand tubes and thimble type tube plugs. 
     Another feature of the present invention is a high pressure fluid supply system that is portable and able to operate in hazardous environments using only a supply of compressed air to both control and power its pumping system. 
     A further benefit of this invention is the use of a mandrel that has an inward threaded end, that may be secured in threaded engagement with a previously installed plug, to facilitate the removal of a plug when further servicing or tube replacement may be required. 
     These and other objects may become more apparent to those skilled in the art upon review of the summary of the invention as provided herein, and upon undertaking a study of the description of its preferred embodiments, in view of the drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational view of the tube plug of this invention embodying the principles of this invention; 
         FIG. 1A  is an axial section view of the tube plug taken upon the line A-A of  FIG. 1 ; 
         FIG. 2  is an exploded view of the high pressure expansion mandrel embodying and showing the variety of component parts of this present invention; 
         FIG. 3  is a side view of the high pressure expansion mandrel located within a tube plug as shown in  FIG. 1 , with all shown being inserted into a tube located one of the tubes found in boilers, condensers, and the like; 
         FIG. 3A  is a sectional view of the high pressure expansion mandrel, as located in a tube plug, and shown within the tube being plugged, taken along the line A-A of  FIG. 3 ; and 
         FIG. 4  is a schematic view of the high pressure fluid supply system showing the relationship of the various components of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In referring to the drawings; and in particular to  FIG. 1 , the tube plug  1  is a cylindrical housing member that can be made of but not limited to the following materials: high strength steel, stainless steel, brass, titanium, and other highly engineered composite materials, that can be expanded using high pressure hydro-expansion tooling and techniques. It is sized for insertion within the end portion of a tube or an annular bore in a metal sheet i.e. tube-sheet, for a boiler, condenser, and other type heat exchanger. A portion of the outer surface of the plug  1  may or may not have concentric ridges and grooves  2  to grip the inside of the tube and create a seal, and may or may not have a flange  3  located at one end to control the depth of plug insertion into the tube. The plug  1  has an axial blind bore  4  comprising a smooth portion  5  which may or may not communicate with smaller diameter threaded portion  6 . This threaded portion  6  when included is used for attaching various plug extraction tools (not shown) and can be used for attaching internal plug support structures (not shown) in various versions of the plug. 
     Now referring to  FIG. 2 . The hydraulic expansion apparatus for setting the tube plug  1  in place includes a mandrel assembly  7  made up of the following components. The components are made of appropriate high strength materials such as but not limited to, steel, stainless steel, titanium, high strength metal alloys, plastic ceramics and can vary depending on the application and any special environmental needs. A mandrel shaft  8  made of an appropriate high strength material and has an increased diameter section  9  at one end which has a beveled surface  10  on the inboard side where it joins with the reduced diameter portion of the shaft  11  and a threaded section  12  at the opposite end of the shaft. It should be noted that the mandrel  8  is generally formed of a uniformed diameter along it length except for its end  9 , so that the components mounted thereon can be slid off and replaced when required. 
     Outboard of the threaded section  12  is a suitable high pressure connector  13  capable of joining the shaft to a 20,000 psi to 60,000 psi variable pressure fluid supply in the operation of the mandrel assembly  7  for the expansion of the tube plug  1 . O-ring  14  and a polyurethane backup ring  15  sit in a recess  16  formed in the shaft  8  outboard of the threaded section  12  of the shaft  8 . Suitable annular grooves  17   a  and  17   b  are formed in the reduced section of the shaft  11 . Seated in the grooves  17   a  and  17   b  respectively are O-rings  18   a  and  18   b  made of a suitably soft material. Outboard and adjacent to O-rings  18   a  and  18   b  are polyurethane backup rings  19   a  and  19   b  made of a resilient composition that are considerably harder than the O-rings  18   a  and  18   b  but will deform in a plastic manner when placed under extremely high pressure. These backup rings  19   a  and  19   b  are of a slightly larger diameter than the increased diameter section  9  on the mandrel shaft  8  to better enable them to fill the annular extrusion or expansion gap for the mandrel assembly  7  as defined by the outer surface of the increased diameter section  9  on the mandrel shaft  8  and the inner wall of the tube plug  5 . The backup rings  19   a  and  19   b  tend to prevent destructive deformation to the O-rings  18   a  and  18   b , respectively by acting as a barrier between the O-rings  18   a  and  18   b  and other components disposed on the mandrel shaft  8  outboard of the backup rings  19   a  and  19   b.    
     A spacer  20   a  made of an appropriate high strength material with an ID slightly larger than the OD of the reduced diameter section  11  of the mandrel shaft  8  to allow it to slide freely in an axial direction on the mandrel shaft  8 . Spacer  20   a  has a small diameter cross bore  20   d  to facilitate the free flow of pressurized fluid through and around the spacer. This allows for the removal of the pressure spacer  20   a  from the mandrel shaft  8  which facilitates the installation and removal of various components that are disposed on the mandrel shaft  8  between the groove  17   b  location and the increased diameter section  9  of the shaft. The OD of the pressure spacer  20   a  should be slightly less than the increased diameter section  9  of the mandrel shaft  8 . The spacer  20   a  is disposed on the mandrel shaft  8  between grooves  17   a  and  17   b  to provide separation for O-rings  18   a  and  18   b  and to assist them in maintaining their desired position in the grooves  17   a  and  17   b  when inserting and removing the mandrel assembly  7  axially in and out of the tube plug  1 . 
     Outboard of the backup rings  19   a  and  19   b  are segmented ring assemblies  22   a  and  22   b . The segmented ring assemblies  22   a  and  22   b , comprise, respectively four to eight equal sized segments, more or less, made of a high strength steel alloy and held together by elastic bands or O-rings  23   a  and  23   b . The number of segment pieces for each ring assembly is dependent on the size of the application. The elastic bands or O-rings  23   a  and  23   b  rest in grooves formed respectively in the outer annular face of the segment pieces that form the segmented rings  22   a  and  22   b . The ID of the segmented ring assemblies  22   a  and  22   b  is a diameter that allows them to slide along the reduced section  11  of the mandrel shaft  8 . The OD of the segmented assemblies  22   a  and  22   b  should be slightly less than the increased diameter section  9  of the mandrel shaft  8 . On each side of the segmented ring assemblies  22   a  and  22   b  are oppositely directed beveled cam surfaces  24   a  and  24   b.    
     Cam rings  21   a ,  21   b , and  21   c  are annular members that are made of a an appropriate high strength material with an ID that allows them to slide freely on the reduced diameter section  11  of the mandrel shaft  8  and an OD slightly less than the increased diameter section  9  of the mandrel shaft  8 . Each cam ring  21   a ,  21   b  and  21   c  has one end face thereof that is perpendicular to the axis of the mandrel shaft  8 . Each cam ring  21   a ,  21   b  and  21   c  has an opposite beveled end face  25   a ,  25   b  and  25   c  respectively. The cam rings  21   a ,  21   b  and  21   c  are disposed on the mandrel shaft  8  with one inboard of the segmented ring assembly  22   a  and one inboard and outboard of the segmented ring assembly  22   b  with their beveled end facing its associated segmented ring assembly, conforming to or matching the beveled surface confronting therewith. 
     Outboard of cam ring  21   c  are disposed annular spacers  20   b  and  20   c  made of an appropriate high strength material with an ID slightly larger than the OD of the reduced diameter section of the mandrel shaft  11  to allow it to slide freely in an axial direction on the mandrel shaft  8 . The OD of the spacers  20   b  and  20   c  should be slightly less than the increased diameter section  9  of the mandrel shaft  8 . Spacer  20   b  has a small diameter cross bore  20   e  to facilitate the free flow of venting fluid through and around the spacer. The spacers assist in positioning the components on the mandrel shaft  8  between groove  17   a  and the threaded section  12  of the mandrel shaft  8 . Outboard of the spacer  20   c  is a locking nut  26  that is secured in threaded engagement with the threaded section  12  of the mandrel shaft  8  and limits the axial travel of the components on the mandrel shaft  8  in the direction of the locking nut  26 . 
     Now referring to  FIGS. 1 ,  2  and  3 . The tube plug  1  is inserted axially into a tube  27  which is disposed in a bore of a metal sheet  28  i.e. a tube sheet. The high pressure expansion mandrel assembly  7  is inserted axially into the blind hole bore  4  of the tube plug  1 . As the mandrel assembly  7  enters the tube plug  1 , the O-ring  18   b  seals against the smooth bore  5  of the tube plug  1 . Air or liquid that may be trapped between this sealing point in the blind hole area  4  of the tube plug  1  is vented through an axial bore or vent passage  29  in the mandrel shaft  8  which intercepts a cross bore  30  located out board of O-ring  18   a  and the opposite end of the expansion zone  31 . The expansion zone  31  is defined as the area between the sealing points of O-rings  18   a  and  18   b . This venting action prevents a hydraulic lock condition from taking place when inserting or removing the mandrel assembly  7  into or from a blind bore such as the one in a tube plug  1 . A suitable fluid such as but not limited to distilled water from a high pressure pump system capable of supplying fluid at variable and controllable pressures between 20,000 pi and 60,000 psi is supplied via a suitable umbilical connection, is injected into the plug  1 . These high pressure supply systems may be engineered to utilize pneumatic controlled logic or electronic and digital control logic or a combination of both. The fluid enters the mandrel shaft  7  via an axial bore  32  in the center of the mandrel shaft  7  which terminates at the intersection of a cross-bore  33  in the expansion zone  31  area which is located between O-rings  18   a  and  18   b . The fluid under pressure is contained in the annular extrusion or expansion gap in the expansion zone  31  located axially between O-rings  18   a  and  18   b  on the mandrel assembly  7 . The contained pressurized fluid pushes the O-rings  18   a  and  18   b  and causes them to leave the grooves  17   a  and  17   b  respectively and slide along the mandrel shaft  8  in an axial direction outward. The O-rings  18   a  and  18   b  come in contact with the backup rings  19   a  and  19   b  respectively and cause them to slide in an axial direction outward on the mandrel shaft  8 . As the backup rings  19   a  and  19   b  come in contact with the cam rings  21   a  and  21   b  they move them in an axial direction outward and into contact with the segmented rings  23   a  and  23   b  respectively. The segmented ring  23   a  is moved further outward in an axial direction until it comes in contact with the beveled surface  10  of the increased diameter section  9  of the mandrel shaft  8 . Concurrently the segmented ring  22   b  is moved in an axial direction outward and as it comes in contact with the cam ring  21   c  it moves cam ring  21   c  in an axial direction outward until cam ring  21   c  comes in contact with spacer  20   b . As the fluid pressure increases the axial movement of the components cause the beveled surfaces  25   a ,  25   b , and  25   c  of cam rings  21   a ,  21   b , and  21   c  respectively along with the beveled surface  10  of the mandrel shaft  8  to engage with the oppositely directed conforming walls of the segmented rings  22   a  and  22   b  respectively. This action causes the segmented ring assemblies  22   a  and  22   b  to expand radially during the radial expansion of the extrusion gap which is taking place concurrently under the force of the high pressure fluid. As the segmented rings  22   a  and  22   b  expand radially they remain in contact and parallel to the axis of the tube plug  1  and form a barrier to prevent the softer material of the backup rings  19   a  and  19   b  from extruding in an axial direction outward. As the high pressure fluid continues to enter the annular gap in the expansion zone  31  through the port  33 , it expands the tube plug  1  radially. As pressure increases the plug  1  goes into plastic deformation until it makes contact with the interior of tube  27 . Additional pressure stresses the tube  27  and tube sheet ligament  28  but always within the ligaments elastic range. As the plug wall expands, the ridges  2  on the plug  1  O.D penetrate the inner wall of the tube  27  slightly, interlocking with the tube  27  and thereby creating multiple interlocking sealing rings between the tube plug  1  and the tube  27 . When pressure is released the tubesheet  28  material returns to its original shape and position and the result is a tight interfacial fit between the O.D. of the tube plug  1  and the I.D. of the tube  27 . 
     Now referring to  FIG. 4  which is a schematic of a high pressure fluid supply system  34  showing the relationship of the components used to generate and control the fluid used to expand the tube plug in  FIG. 1 . Fluid is taken from a reservoir  35  and supplied through a shutoff valve  36 , particulate filter  37 , and one-way check valve  38  to an air-over-hydraulic pump  39 . Low pressure compressed air between 80 psi and 160 psi is supplied to the unit as read on inlet air pressure gauge  40 . This air is supplied to two regulators  41  and  42 . Regulated pressure from one regulator  42  is indicated by pressure gauge  43  as the air is routed to a normally closed air pilot valve  44 . The regulator  42  will govern the maximum available output pressure of the hydraulic pump  39  by controlling the inlet air pressure. Air pressure from the second regulator  41  is indicated on a pressure gauge  45  as it is supplied to a normally open air pilot valve  46  and to a manually operated 3-way air valve  47 . The system is activated when the operator selects the open position of air valve  47  and thus supplies regulated air to the normally open air pilot valve  46  closing it and to an air pilot operator  48 . Air pilot operator  48  activates a normally closed air valve  49  which in turn opens and directs regulated air to activate a normally closed air pilot valve  44 . The air pilot valve  44  opens and directs regulated air to the air side of the hydraulic pump  39  causing the pump  39  to operate. The hydraulic pump  39  begins to pump fluid past the outlet check valve  50  to the manual relief valve  51  and the high pressure out conduit  52 . When the manual relief valve  51  is closed and the high pressure out conduit  52  is restricted, system output pressure will increase and will be indicated on the output pressure gauge  53 . When the operator closes the 3-way air valve  47  the pressurized air to the air pilot valve  46  and the air pilot operator  48  is terminated. This causes the air valve  49  and air pilot valve  44  to return to their normally closed positions which shuts off the supply of pressurized air to hydraulic pump  39  which causes the hydraulic pump  39  to cease cycling. With the pressurized air removed from air pilot valve  46 , it returns to the open position and relieves the pressure trapped in the high pressure out conduit  52  and returns the fluid to the reservoir  35 . 
     Variations or modifications to the subject matter of this invention may occur to those skilled in the art upon review of the invention described herein. Such variations, if within the spirit of this invention, are intended to be encompassed within the scope of any claims to patent protection issuing hereon. The specific description of the invention as set forth in the specification, and as depicted in the drawings, are set forth for illustrative purposes only.