Patent Publication Number: US-2022234130-A1

Title: Method for pipe purging

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to U.S. Provisional Patent Application No. 63/142,088, filed Jan. 27, 2021, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Reactive metals will react with oxygen when at or near their melting point. These reactions result in oxide formations to the weld which can be detrimental to the mechanical properties and corrosion resistance of the weld. In such applications it is often necessary to purge the inside atmosphere to 10 to 50 ppm (parts per million) of oxygen. This often requires a considerable amount of time and gas depending on the methods employed and the total volume (eg: standard cubic feet) to be purged. 
     The most commonly used method is inefficient regarding both time and volume of gas required to reach a predetermined rest oxygen level (ppm). There are effective methods in existence such as purge systems which consist of 2 inflatable bladders installed on each side of the joint to be welded, sealing off a small section (typically 12″) of the inside of the pipe in the immediate area where the inside of the weld will be. Once the area is sealed, the purge gas is introduced to the sealed off section through a small gas diffuser (typically 0.75″ diameter or less). The purge gas fills the sealed section of the inside of the pipe, replacing with the inert atmosphere, While these are effective, they are not applicable in all circumstances due to length, size and or configuration of the piping system. 
     One of the primary challenges to effective, efficient purging is minimizing the amount of mixing or dilution of the purge gas and the atmosphere to be purged. Typically, the diffuser end of the purge gas supply line is far less in diameter than the inside diameter of the pipe to be purged (ex; 3/4″ diffuser into a 12″ diameter pipe). The inherent effect will be that the purge gas mixes with the atmosphere inside the pipe for considerable time. 
     Industrial pipe systems involve multiple pipe configurations, involving various diameters and wall thicknesses often joined to one of numerous connection elements such as flanges, elbows, T-type fittings etc. Drawings as representations of a pipe section that needs to be created are drafted by engineers. These drawings provide the details of the angles, fitting sizes, weld types and sizes in addition to other specifications needed to create the desired pipe structures. The assembly process generally begins with preparing the segments. For full penetration welds, bevels are typically created on the pipe ends along with other pipe end or surface preparations. Next the components are generally tack welded together to align the pipe sections for single or multi-pass welding. 
     It is common that weld procedures require a maximum oxygen level (and sometimes nitrogen) to be achieved prior to welding (rest oxygen level) and maintained until the weld is complete or until the root pass will not be re-heated to susceptible temperature by subsequent weld passes. The process of performing single or mufti-pass full penetration welds generally involves the steps of a) purging the inside of the pipe to the required rest oxygen ppm level, b) maintaining the rest oxygen level until welding is complete or enough passes have been completed so the root pass can no longer reach a susceptible temperature, c) creating a first weld seal (root pass) of two section of pipe, d) performing a subsequent weld over the previous weld, and e) repeating step d) until the piping sections are fully welded together across the thickness of the pipe wall, including weld reinforcement. 
     A major materials issue with multi-pass welding of pipes is the structural integrality of the resulting weld. it is critical in e.g. nuclear reactors, that pipes handling reactor coolant not fail due to rupture. A stress fracture of key pipes in a refinery could result in catastrophic failure causing great damage and endangering many lives. it is thus essential that these welded structures adequately withstand the extreme conditions to which they are exposed. 
     Thus, there is a need in the industry to effectively and efficiently purge the atmosphere from the inside of a given length or assembly of pipe and replace the ambient atmosphere with an inert atmosphere prior to, and during welding. 
     SUMMARY 
     A method of providing an inert atmosphere to the inside of a piping assembly prior to and during welding, including introducing a canister, and a deflated bladder which surrounds the canister, into a piping assembly to be welded. Introducing purge gas, thereby inflating the deflated bladder and sealing the canister against the inside of the piping assembly to be welded. Introducing excess purge gas from the bladder into a primary purge gas diffuser, thereby producing a first diffused purge gas stream. Introducing the first diffused purge gas stream into a secondary purge gas diffuser, thereby producing a secondary diffused purge gas stream, Introducing the secondary diffused purge gas stream into a tertiary purge gas diffuser, thereby producing a third purge gas stream. And introducing the third purge gas stream into the inside of the piping assembly to be welded. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein: 
         FIG. 1  is a schematic representation of the internal pipe inerting device inserted and operation, in accordance with one embodiment of the present invention. 
         FIG. 2  is a schematic representation of the internal pipe inerting device with deflated bladders prior to insertion into the piping assembly to be welded, in accordance with one embodiment of the present invention. 
         FIG. 3  is a schematic representation of the internal pipe inerting device with deflated bladders after insertion into the piping assembly to be welded, in accordance with one embodiment of the present invention. 
         FIG. 4  is a schematic representation of the internal pipe inerting device with inflated bladders after insertion into the piping assembly to be welded, in accordance with one embodiment of the present invention. 
     
    
    
     ELEMENT NUMBERS 
       100 =internal pipe inerting device 
       101 =canister 
       102 =bladder 
       102   a =deflated or underinflated bladder 
       102   b =inflated bladder 
       103 =pipe wall 
       104 =purge gas source 
       105 =purge gas supply conduit 
       106 =purge gas inlet connection 
       107 =bladder fill conduit 
       108 =bladder return conduit 
       109 =pressure relief device 
       110 =reduced pressure purge gas conduit 
       111 =primary purge gas diffuser 
       112 =first diffused purge gas stream 
       113 =secondary purge gas diffuser 
       114 =second diffused pure gas stream 
       115 =tertiary purge gas diffuser 
       116 =purge gas exit holes 
       117 =third diffused purge gas stream 
       118 =pipe interior volume 
       119 =piping assembly to be welded 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     As discussed above, the typical systems in industrial use presently often result in a mixture of both atmosphere and the purge gas exiting the exhaust hole or port in the piping system being purged, until eventually most of the oxygen is expelled. The present apparatus is designed so that the total area (in 2 ) of the diffused purge gas entering the inside of the pipe will be equal to or near equal to the inside diameter of the pipe being purged. This significantly minimizes the purge gas mixing with the atmosphere which will provide a more efficient, effective and stable purge. The time and gas volume required is significantly reduced. 
     Turning to  FIG. 1 , internal pipe inerting device  100  includes canister  101  and bladder  102 . Bladder  102  may be a cylindrical shell configured to surround canister  101  and contact the inside wall  103  of the section of pipe to be welded  119 . Purge gas supply conduit  105  is attached to both purge gas inlet connection  106  on canister  101  and purge gas source  104 . The purge gas flows through bladder fill conduit  107 , which resides inside of canister  101 , and then into bladder  102 , subsequently inflating bladder  102 . Bladder  102  is designed such that when fully inflated, the outside diameter is equal to, or preferably slightly greater than, the maximum inside diameter for each nominal pipe size. Once inflated, bladder  102  seals canister  101  inside the section of pipe to be welded  119 . 
     Excess purge gas then exists through bladder return conduit  108  and into pressure relief device  109 . Reduced pressure purge gas conduit  110  then enters primary purge gas diffuser  111 . First diffused purge gas stream  112  exits primary purge gas diffuser  111  and is more evenly spread throughout the interior volume of canister  101 . First diffused purge gas stream  112  then enters secondary purge gas diffuser  113 . Second diffused purge gas stream  114  exits secondary purge gas diffuser  113  and is still more evenly spread out. Second diffused purge gas stream  114  then enters tertiary purge gas diffuser  115 . Third diffused purge gas stream  117  then exits canister  101  through purge gas exit holes  116  and fills pipe interior volume  118 . 
     In one embodiment of the present invention, primary purge gas diffuser  111  may be made up of coils of perforated tubing used to initially disperse the purge gas into the initial reservoir of canister  101 . Secondary purge gas diffuser  113  may be made up of layers of steel wool for diffusion. Tertiary purge gas diffuser  115  may be made up of a metal screen affixed to the end of canister  101  for further diffusion prior to entering interior pipe volume  118 . This ensures that the area of the purge gas is equal to or near equal to the ID of the pipe which significantly increases the efficiency and effectiveness of the purging process. 
     Purge gas source  104  may be cylinders (liquid or high pressure) or other means including bulk, micro bulk, on-site generation. Pressure and flow may be regulated prior to entering the canister. 
     Canister  101  may be a cylindrical container made of metal or other durable material. Canister  101  may have a length CL of between 3″ and 12″, preferably between 3″ to 6″ depending on the nominal pipe size. Canister  101  may have a length CL greater than 12″ depending on the pipe diameter. The canister  101  may have a diameter CD that is equal to approximately 1″ less than the smallest inside diameter ID of each nominal pipe size ranging from 4″ to 36″. As used herein, the term “approximately 1″ less” is defined as being between 3/4″ and 1¼″, preferably between ⅞″ and 1⅛″ less than the ID of the pipe. Canister  101  may be closed, air-tight on the inlet end, with purge gas inlet connection  106  which may include an inert gas fitting. The outlet end of canister  101  is covered with a metal screen which may act as tertiary purge gas diffuser  115 . There may be additional purge gas exit holes  116  or ports around the perimeter of canister  101 , located near the outlet end to allow purge gas to flow into the annular space between the canister and the pipe walls. 
     Bladder  102  may be constructed of a flexible, heat and tear resistant material capable of withstanding up to  50  psig pressure. Bladder  102  is inflated and pressurized by the purge gas. Once inflated, bladder  102  seals off the inside of the pipe preventing further atmospheric contamination. Bladder  102  is continuous around the perimeter of canister  101  to which it may be permanently affixed and sealed. 
     Pressure relief device  109  may be is a low-pressure relief device located inside canister  101  immediately downstream of bladder  102 . Purge gas flows from bladder  102  to pressure relief device  109 , which provides adequate back pressure to bladder  102  in order to maintain pressure (app. 10-50 psig) to the bladder. The purge gas then flows from the pressure relief device  109  to primary purge gas diffuser  111 . 
     Primary purge gas diffuser  111  may be made of coils constructed of a durable heat resistant material such as copper or stainless steel tubing. The coils may be situated around the inside perimeter of canister  101  with inwardly facing holes or ports to provide multiple purge gas outlets to the inside of canister  101 . The diameter, spacing and number of holes and/or coils may vary depending on the nominal pipe size designed for. 
     Secondary purge gas diffuser  113  may include layers of generic steel wool which are situated inside canister  101  immediately downstream of the primary purge gas diffuser  111 . The purge gas may flow from the perforated coils through the steel wool which further diffuses the purge gas stream prior to exiting through the diffuser screen. The size and thickness of the steel wool may vary according to the nominal pipe size the canister is designed for. 
     Tertiary purge gas diffuser  115  may include a diffuser screen which is constructed of metal and is permanently affixed to the outlet end of the diffuser. The screen provides additional diffusion of the purge gas as it enters the inside of the pipe. 
     In some situations, related to full penetration welds, the weld area must be free from oxygen and sometimes nitrogen if desired. The devices and methods described herein provide a readily adopted way of providing an inert atmosphere in the weld area which would be free from oxygen and/or nitrogen depending on the purge gas chosen. 
     An apparatus suitable for practicing the invention herein may include a number of other components including an oxygen analyzer/monitor to provide a continuous monitoring of the oxygen levels prior to and during welding. 
     Turning now to  FIGS. 1-4 , a method of inerting an internal volume of a pipe to be welded is shown. Internal pipe inerting device  101 , as described in detail above, is prepared for insertion into the piping assembly to be welded  119 . As indicated in  FIGS. 2 and 3 , at this time, bladder  102   a  is deflated or underinflated, in order for internal pipe inciting device  101  to be inserted. 
     As indicated in  FIG. 4 , once internal pipe inerti108ng device  101  is inserted into the desired location within the piping assembly to be welded  119 , pressurized inert gas is delivered from purge gas source  104 , through purge gas supply conduit  105 . The purge gas then passes through purge gas inlet connection  106 , through purge gas fill conduit  107 , and into bladder  102   b,  which inflates. As bladder  102  inflates, it forms a seal between canister  101  and the piping assembly to be welded  119 . 
     Once bladder  102   b  has reached the desired sealing pressure, purge gas then reenters canister  101  through bladder return conduit  108 . As indicated in detail in  FIG. 1 , pressure relief device  109  the reduces the pressure of the purge gas and introduces it into the primary purge gas diffuser  111 . First diffused purge gas stream  112  exits primary purge gas diffuser  111  and is more evenly spread throughout the interior volume of canister  101 . First diffused purge gas stream  112  then enters secondary purge gas diffuser  113 . Second diffused purge gas stream  114  exits secondary purge gas diffuser  113  and is still more evenly spread out. Second diffused purge gas stream  114  then enters tertiary purge gas diffuser  115 . Third diffused purge gas stream  117  then exits canister  101  through purge gas exit holes  116  and fills pipe interior volume  118 . 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.