Abstract:
A corrosion sensor ( 20 ) for sensing corrosion includes a housing ( 28 ) and a device ( 36 ) for jointing the housing ( 28 ) to a wall of a pipeline ( 10 ) that receives a fluid ( 24 ). The sensor ( 20 ) also includes a rupture member ( 44 ) which extends across a portion of the housing ( 28 ) to define a seal chamber ( 48 ) in the housing ( 28 ). The rupture member ( 44 ), upon rupture, provides an opening to the sealed chamber ( 48 ). The rupture member ( 44 ) is formed of a material and thickness such that the rupture member ( 44 ) will fail from corrosion before the enclosure wall will fail from corrosion. The sensor also includes a sensory device ( 100 ) which is connected to the housing ( 28 ) at the sealed chamber ( 48 ) to signal a rupture condition.

Description:
This application is a §371 of PCT/US97/12050 filed Jul. 11, 1997 which is a continuation of application Ser. No. 08/891,120 filed Jul. 10, 1997, now U.S. Pat. No. 5,948,971, which is a continuation of application Ser. No. 60/021,890 filed Jul. 17, 1996, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a corrosion sensing device and more particularly to a corrosion sensor that can be positioned at a desired location in a pipeline system to detect corrosion in the pipeline system. 
     Pipeline corrosion is generally a hidden problem that often cannot be controlled in many industrial settings. In the chemical industry, corrosion activity can limit equipment life and threaten the reliability of industrial installations. Useful materials in process fluids can cause corrosion of the apparatus used to handle such fluids resulting in a need to curtail operations or shut down a processing system. Correcting the effects of corrosion can thus lead to high maintenance costs. Since it is not often feasible to control corrosion, the effects of corrosion are usually dealt with by removing and replacing the afflicted structure at an estimated stage of corrosion damage. 
     Thus, one known remedy for dealing with pipeline corrosion is to replace sections of a pipeline at predetermined time intervals rather than risk pipeline rupture and system shutdowns. However, this procedure can be unduly expensive if pipeline is replaced too soon when it still has substantial useful life. Therefore, one of the problems in dealing with pipeline corrosion is accurately determining the optimum time to replace a pipeline. 
     If information on the extent of corrosion activity is obtainable before significant damage occurs, remedial measures can be taken to repair process equipment before the corrosion activity leads to equipment failure. Thus, an effective corrosion monitoring program typically begins with obtaining information on the extent of corrosion damage or corrosion activity occurring in a particular installation. With regard to pipeline corrosion, a variety of different techniques have been used for determining the amount of corrosion damage or corrosion activity that has occurred in a pipeline used for conveying process fluids. 
     U.S. Pat. Nos. 4,328,462, 4,768,373 and 5,571,955 disclose the use of probes which are inserted into containers or pipes holding a fluid that causes the pipe or container to corrode. The probes react to the corrosive influence of the fluid in a known correlation to the corrosive response of the material forming the container or pipe. However, the pressures and temperatures often associated with chemical processes severely limit the opportunity to install and remove such probes from the container or pipe, thus limiting access to information on corrosion activity that they are designed to provide. 
     Other known techniques for determining corrosion activity of process fluids rely on sampling of the process fluids in a processing structure in order to detect corrosive agents or corrosion by-products correlated to corrosion activity. However, sample testing is often time consuming and can thus impose considerable delay between the time of sampling and the reception of analytical results of corrosion tests. 
     U.S. Pat. No. 4,389,877 describes a system to monitor the amount of erosion taking place within a pipe. Notches are formed in the wall of the pipe to provide an area of reduced strength. A hollow, sealed casing is built around the pipe at the point of reduced strength to provide a leak-tight chamber. A conduit from the hollow, sealed casing is connected to an outside sensing device to monitor pressure changes in the casing. A predetermined pressure change will indicate when a pipe failure occurs at the portion of reduced strength. However, the need to provide areas of reduced strength and a hollow casing around the areas of reduced strength with special sealing material and a sealing collar make it difficult and expensive to employ the &#39;877 system. Moreover, the &#39;877 system allows monitoring only of the pipe area that is notched and sealed with a casing. Thus, areas of the pipeline system which are not easily accessed cannot be monitored. Consequently, remote areas of a pipeline system that might be vulnerable to corrosion failure do not receive adequate monitoring. 
     It is therefore desirable to provide a reliable method and means for detecting corrosion anywhere in a pipeline system, which means is easily connected to a pipe or sections of pipe and can be used under conditions of high temperature and/or pressure. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     One of several objects of the invention is the provision of a novel method and means of accurately detecting corrosion anywhere in a pipeline system. Another object of the invention is the provision of a novel method and means of accurately detecting when corrosion in a pipeline system has reached a predetermined level. Another object of the invention is the provision of a novel method and means of detecting corrosion of a pipeline system without the need to sample the fluid or to insert a probe into the fluid. Yet another object of the invention is the provision of a novel method and means of accurately detecting corrosion of a pipeline system under conditions of high temperature and/or high pressure. Yet still another object of the invention is the provision of a novel method and means of securing a corrosion detector in a pipe without altering the existing pipe structure. 
     In accordance with the present invention, a corrosion sensor is provided which includes a housing and a device for joining the housing to a wall of an enclosure that receives a fluid. The sensor also includes a rupture member which extends across a portion of the housing to define a sealed chamber in the housing that is maintained at a predetermined pressure. The rupture member is formed of a material that is structured to fail from corrosion before the enclosure wall is subject to corrosion failure. The rupture member is joined to the enclosure such that fluid received in the enclosure can contact the rupture member under similar conditions in which the fluid contacts the wall of the enclosure. The rupture member, upon rupture due to corrosion, provides an opening to the sealed chamber and thus changes the pressure conditions inside the chamber. The corrosion sensor also includes a sensing system which is connected to the housing at the sealed chamber to signal a rupture condition of the rupture member when the sealed chamber opens. The sensing system includes a pressure sensor and signaling device that cooperates with the pressure sensor to provide a signal in response to predetermined pressure levels measured by the pressure sensor. 
     In one embodiment of the invention, the rupture member includes a rupturable section which comprises an area of predetermined, reduced thickness relative to the thickness of the rupture member. 
     The invention also provides a method of sensing corrosion in a pipeline system. The method includes conveying a fluid within a pipeline system that includes at least one wall formed of a material that is vulnerable to corrosion. The method further includes joining a sensor to the pipeline system such that fluid flows through one section of the pipeline system and past the sensor to another section of the pipeline system. The method also includes providing a rupture member in the sensor to form a sealed chamber and arranging the rupture member such that fluid flowing through the one pipe contacts the rupture member. The method further includes forming the rupture member of a material structured to fail from corrosion before the wall of the pipeline system fails from corrosion. The method also includes providing a signal when the rupture member ruptures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawing, 
     FIG. 1 is an upright, sectional view of a system for detecting corrosion in a pipeline, incorporating one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a pipe system  10  includes a first pipe section  12  and a second pipe section  16  joined by a corrosion sensor  20 . The pipe sections  12  and  16  are of a known construction and can be formed from a metal such as stainless steel  304 . The pipes  12  and  16  convey a process fluid  24  of low pH value in the range of zero to 5 such as acidic water. The process fluid  24  can have a temperature of approximately 450 degrees F. and a pressure of approximately 1200 p.s.i.g. The corrosion sensor  20  includes a housing  28  having a T-section  32  and a bell section  34  joined together about a rupture member  44 . The housing  28  can be formed from the same material as the pipes  12  and  16 . 
     The T-section  32  has opposite pipe joining ends  36  and  40  for connection with the first and second pipe sections  12  and  16  respectively in any suitable, known manner, such as welding with or without threading. The T-section  32  also includes a neck portion  52  intermediate the pipe joining ends  36  and  40  which neck portion  52  terminates in a flange  38 . In some instances, under relatively low fluid flow rates, a flow deflector  76 , preferably made of a non-corrodible material, such as ceramic, can be mounted in the T-section  32  between the ends  36  and  40  and opposite the rupture member  44 . The flow deflector  76  has a flow deflection surface  78  to direct the flow of the process fluid  24 , as indicated by arrow  80  into the neck portion  52  against the rupture member  44 . Thus, a portion of the fluid  24  passing through the pipe sections  12  and  16  can be directed toward the rupture member  44  by the flow deflector  76 . 
     The rupture member  44  includes a fluid exposed surface  84  which can be disposed above the fluid flow path and over the fluid deflector  76 . The pipes  12  and  16  can have an inner diameter of approximately six inches and a wall thickness of approximately one to two inches. The fluid exposed surface  84  of the rupture member  44  can be flush mounted in any suitable known manner with the inner surface of the pipe or recessed approximately one to two inches from the inside diameter of the pipe joining ends  36  and  40 . Upward disposition of the rupture member  44  when the fluid exposed surface  84  is recessed helps to avoid accumulation of sediment or other debris from the process fluid  24  on the fluid exposed surface  84 . Sediment accumulation on the exposed surface  84  of the rupture member  44  is likely to occur if the recessed rupture member  44  is located under the fluid flow path. The rupture member  44  can be formed of a metal similar to the metal of the pipe sections  12  and  16 , but of lesser thickness such as ½ the wall thickness of the pipe section  12  and  16 . If desired, the rupture member can be formed from a metal, such as carbon steel, which corrodes at a faster rate than the pipes  12  and  16 . 
     When the rupture member  44  is of the same material as the pipe sections  12  and  16  and half as thick as the pipes  12  and  16 , failure of the rupture member will occur approximately twice as quickly as the pipes  12  and  16 . If the rupture member is formed of carbon steel of equal thickness as the pipes  12  and  16 , the rupture member  44  is also likely to fail in a quicker time than it takes for the pipe to fail. The relative time difference between rupture of the rupture member  44  and rupture of the pipe sections  12  and  16  can be predetermined based on the specific characteristics of the fluid medium that is conveyed by the pipe. 
     If desired, the rupture member  44  can be formed with a rupturable section  68  of reduced wall thickness with respect to the remainder of the rupture member  44 . The rupturable section  68  can, for example, be formed as the remaining thickness below a small diameter, blind hole  88  which can be drilled or bored into the rupture member  44 . The rupturable section  68  can, for example, be formed with a thickness of one half the thickness of the pipes  12  and  16  if the rupture member is formed of stainless steel. 
     The bell section  34  defines a chamber  48  having an open end with a flange  42 . The rupture member  44  is sandwiched between the T-section flange  38  and the bell section flange  42  which are joined together in any suitable, known manner to form a leak tight joint. The chamber  48  is thus sealed and preferably maintained at ambient pressure by a pressure bleed valve  104 . 
     A sensing device or sensor  60  for signaling a rupture condition of the rupturable section  68  of the rupture member  44  is joined to the bell section  34  by a conduit  64  that communicates with the chamber  48 . The sensor  60  includes a conventional pressure valve  98  on the conduit  64  that communicates with a pressure detector or pressure indicator  96 . A conventional alarm or signal system  100  communicates with the pressure detector  96 . 
     In operation of the pipe system  10  and the corrosion sensor  20 , the process fluid  24  is conveyed through the pipes  12  and  16 . The flow deflector  76 , which is optional, especially in flow systems under relatively high pressure such as 1200 p.s.i.g., helps direct the process fluid  24  into the neck portion  52  of the T-section  32  and against the rupture member  44 . After a predetermined time, the pipes  12  and  16  will experience corrosion as a result of exposure to the process fluid  24 . The flow deflector  76  is usually omitted if there will be relatively heavy particulate matter in the liquid flowing through the pipes  12  and  16  such as ash, corrosion scale and soot. 
     The rupture member  44 , whether formed of the same material or of a different material than the pipes  12  and  16 , is arranged to experience corrosion failure before the pipes  12  and  16 . The rupture member  44  can thus be structured to fail at a predetermined fraction, e.g. one-half, of the anticipated life of the pipeline. Thus, when the rupture member  44  fails, a predetermined amount of pipe life remains before it will also fail. 
     Rupture of the rupture member  44  permits the fluid  24 , usually under high pressure, to enter the corrosion chamber  48 . The pressure detector  96  detects a rupture condition by sensing a change in the ambient pressure in the chamber  48  which is now at the pressure of the pipe system  10 . The pressure detector  96  activates the alarm  100  at a predetermined pressure to indicate that a failure of the rupture member  44  has occurred. 
     Since the rupture member  44  is located between the pipe sections  12  and  16  close to the flow path of fluid in the pipe sections  12  and  16 , the flow conditions experienced by the rupture member  44  are substantially the same as the flow conditions in the pipe sections  12  and  16 . Because of the proximity of the rupture member  44  to the pipe sections  12  and  16 , corrosion of the rupture member  44  is representative of the corrosion affecting the pipe sections  12  and  16 . Since the corrosion sensor  20  can be conveniently installed in a pipeline, it is possible to use the corrosion sensor  20  to detect corrosion at substantially all sections of a pipeline. 
     As various changes can be made in the above constructions and method without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.