US 4,998,435 AGrant
Method and Apparatus for Leak Testing of Pipe
Issue Date:1991-03-12
•9 Claims
•6 Drawing Sheets
Abstract
A method of testing pipe sections at an oil rig floor by means of an internal pipe testing tool and a pressurized gas containing helium in a ratio of helium to a carrier gas of at least about 1:2856 by volume. The gas is pressurized in a hydraulic accumulator remote from the rig floor. The pressurized gas actuates the test tool at substantially the same pressure as is used for testing the pipe section. A flexible enclosure confines the test gas which leaks from the pipe section. The enclosure define a substantially annular chamber around the area to be tested to confine leakage test gas to prevent its dissipation into the atmosphere. An aperture is provided in the enclosure to permit a sensing probe to be inserted into the annular chamber between the enclosure and the pipe section to sense the presence of test gas.
Metadata
Assignee
- Damco Testers, Inc.
Inventors
- Ronnie F. Miller
- Arthur L. Dwyer
- Darwin A. Miller
- Darwin L. Miller
Application Information
Application Number:US 2968592
Filing Date:1989-01-13
Priority Date:1983-01-18
Art Unit:265
Classifications
IPC:
G01M 320
Field of Search:
7340.7;49.1;495;46;40.5 R
Patent Drawings (6 sheets)
Description
Brief Description of the Drawings
FIG. 1 is a schematic view showing gas pressurization and leak detection apparatus for testing the leak tightness of pipe joints in accordance with the present invention.
FIG. 2 is a fragmentary perspective view of a pipe section including one form of leak test enclosure in accordance with the present invention.
FIG. 3 is a longitudinal cross-sectional view taken along the line 3--3 of FIG. 2.
FIG. 4 is a transverse cross-sectional view taken
along the line 4--4 of FIG. 2.
FIG. 5 is a fragmentary perspective view of a pipe joint section including another form of leak test enclosure in accordance with the present invention.
FIG. 6 is a transverse cross-sectional view taken along the line 6--6 of FIG. 5.
FIG. 7 is a plan view of the enclosure shown in FIG. 5 after the same has been removed from the pipe and has been fully opened.
FIG. 8 is a fragmentary perspective view of a pipe section showing another form of leak test enclosure.
FIG. 9 is a side view of the preferred pipe testing tool positioned within a pair of interconnected pipe sections to permit pressure testing of the joint therebetween.
FIG. 10 is an enlarged cross-sectional view of the lower mandrel of the preferred testing tool.
FIG. 11 is an enlarged cross-sectional view similar to FIG. 10 but showing the upper mandrel of the preferred testing tool.
FIG. 12 is a cross-sectional view taken along the line 12--12 of FIG. 10.
FIG. 13 is a cross-sectional view taken along the line 13--13 of FIG. 10.
FIG. 14 is a cross-sectional view taken along the line 14--14 of FIG. 11.
Description of the Preferred Embodiments
Referring now to the drawings, and particularly to FIG. 1 thereof, there is shown a section of pipe 10, a portion of which is surrounded by one form of leak test enclosure 12 in accordance with the present invention. The pipe section includes a joint or union 46 by which two portions of pipe are joined together. A detection probe 8 is provided to detect leakage of test gas that is fed under pressure into pipe section 10. The probe is connected to a gas detector 9 to provide either a visual or other convenient indication of leakage of the test gas from inside the pipe section through the joint and into enclosure 12. One type of suitable gas detector that can be used to detect leakage of the test gas is a GOW-MAC Gas Leak Detector, Model No. 21-250, Manufactured by GOW-MAC Instrument Co., Bridgewater, N.J.
The test gas, the composition of which will be described hereinafter in more detail, is provided from a gas source 1 to an accumulator 2, in the form of a pressure vessel, through a pipe 1a, a remotely controlled gas fill valve 1b, and a check valve 1c. Fill valve 1b can be pneumatically or electrically operated from a remote control panel 3 to permit the test gas to enter the accumulator until pressure equilibrium with the gas source takes place, which can be, for example, at a pressure of from about 400 psi to about 1000 psi. Additional pressurization of the gas to the desired test pressure, which can be of the order of about 10,000 psi or more, is obtained by introducing a pressurized liquid, such as water, into the lower portion of accumulator 2 from a water source 4, through pipe 4a, by means of pump 4b. A check valve 4c is provided to prevent backflow and a manually operated relief valve 4d is provided. An isolation valve 4e is provided in the event repairs are desired to be made upstream of valve 4c without relieving the pressure in accumulator 2. A relief valve 4f remotely operated from control panel 3 is provided to permit bleed-off of water, and consequent reduction of pressure, after a pressure test has been completed.
After pressurization of the test gas in accumulator 2 to the desired test pressure, a gas supply valve 5 is remotely operated from control panel 3 to admit pressurized test gas into pipe 6 that is connected with test tool 7 (see FIG. 3) positioned within the pipe. Any temporary reduction in pressure is eliminated by pumping more water into the accumulator. In the form of test tool used in accordance with the present invention, only a single source of pressurized gas is fed to the test tool. The pressurized gas sets the seals of the test tool against the internal wall of the pipe to define the section to be tested. At the same time, the pressurized gas exits from the tool into the annular space between the outside of the tool and inside of the pipe section under test as defined by the set seals. As a result, the pressurized gas which sets the seals of the test tool and the pressurized gas which tests the pipe section for leaks are substantially the same pressure.
After the test has been completed, the relief valves 4d and 4f are opened and the compressed gas in the test tool forces the water, or other hydraulic fluid, back out of the accumulator. These valves remain open until gas starts to escape, after which they are closed. The gas supply valve 5 is also closed, thus trapping most of the gas in the accumulator. The remote atmosphere gas bleed off valve 5a is then opened to allow any gas trapped between the accumulator and the test tool to escape. It is then closed and the cycle can start again.
By this hydraulic system of pressurization of the test gas, the accumulator can be located at a position remote from the rig floor and the control panel. Thus, the control panel can be operated at the rig floor but the sometimes dangerous accumulator can be located where any rupture or breakage due to high pressures will not cause any injury.
As shown in FIG. 2, enclosure 12 includes a generally tubular body 14 which is split longitudinally to define a pair of opposed longitudinal edges 16, 18. Adjacent each of longitudinal edges 16, 118 is a stiffener bar 20, 22, respectively, which can be secured thereto by means of bolts 24, or the like. Stiffener bars 20, 22 each include one element of a locking bar arrangement, stiffener 20 carrying a noticed locking bar 26, and stiffener 22 carrying a notched retainer 28, the arrangement and operation of which will hereinafter be described in more detail. Positioned circumferentially about the outer periphery of the body and suitably secured to stiffener bars 20, 22 are a pair of arcuate handle supports 30, 32, respectively, which extend for approximately 90.degree. of arc in opposite directions around tubular body 14. Extending outwardly from each of handle supports 30, 32 is a spreader handle 34, 36, respectively, each of which preferably is positioned on opposite sides of body 14 to facilitate the separation and spreading of longitudinal edges 16, 18.
Each of the ends of tubular body 14 includes a transversely extending, inwardly directed, resilient seal 38, 40 (only one of which is visible in FIG. 2), that is adapted to sealingly engage the outer surfaces of the pipe sections 42, 44 which are joined by union 46 (see FIGS. 3 and 4), and provide a seal between the respective pipes adjacent the joint and tubular body 14 to prevent dissipation of any test gas that leaks into the annular chamber 48 therebetween. Seals 38, 40 are of generally annular conformation. Flexible seals 50, 52 are positioned along each of longitudinal edges 16, 18, respectively, to assist in preventing the dissipation of any test gas that leaks into annular chamber 48. Although two seals 50, 52 are shown, it is not essential that two seals be used, and a single seal secured to either of longitudinal edges 16 or 18 can be employed, if desired.
The locking means for holding seals 50, 52 in sealing engagement is most clearly seen in FIG. 4. Nothced retainer 28 is positioned on longitudinal stiffener 22 intermediate the ends theeof. Locking bar 26 is pivotally secured to a yoke member 54 which is, in turn, secured to longitudinal stiffener 20 intermediate the ends thereof. Biasing means, such as spring 56, is provided and bears against locking bar 26 outwardly of the pivot 27 to urge the notch thereof toward notched retainer 28. As can be seen in FIG. 4, locking bar 26 and retainer 28 have cooperable notched edges 58, 60, respectively, which are so positioned relative to each other that longitudinal edges 16, 18, respectively, are held in tight engagement when the locking means is engaged.
As best seen in FIG. 3, a typical pipe joint includes a threaded union 46 which engages corresponding external threads on each of adjacent pipe sections 42, 44, and defines part of the inner surface of annular chamber 48. Internal test tool 7 is positioned within the pipe adjacent the joint section to be tested, with upper seal or seals 21 above he joint and lower seal or seals 23 below. Prior to pressurizing the tool, the outside diameter of the seals 21 and 23 are sufficiently smaller than the internal diameter of the pipe of allow the tool to traverse easily therein. Upon pressurization, the seals expand to engage the internal diameter of the pipe and seal the section to be tested, all as fully described in U.S. Pat. No. 4,548,069.
Also provided in tubular body 14 are a probe aperture 62 through which a suitable sensing probe 8 can be inserted in order to sense he presence of leakage gas that flows from a defective joint into annular chamber 48. Additionally, a small vent aperture 64 can be provided to permit the inflow of a small amount of air to replace the gas sample that is withdrawn by the sensing probable. Vent aperture 64 prevents the formation of a slight vacuum, which could otherwise develop if the gas withdrawn through the sensing probe is not replaced by a corresponding volume of air.
Tubular body 14 is preferably formed from a substantially gas impermeable material which is sufficiently flexible to permit the opening of the slot defined by longitudinal edges 16, 18 and at the same time sufficiently resilient to permit enclosure 12 to assume its original shape when the spreading force for opening the slot are relaxed. Suitable materials include flexible sheet metal, or plastics, such as tubular polyurethane, polyvinyl chloride, or the like.
In operation, union 46 is threadedly secured to an end of the pipe section 44, and an end of pipe section 42 is threaded engaged with the upper portion of union 46 to define a complete joint Thereupon test enclosure 12 of the present invention is positioned about union 46 by spreading handles 34 and 36 until longitudinal edges 16 and 18 are separated a distance sufficient to permit the enclosure to be placed over the pipe section. Once enclosure 12 is in position, the spreading forces on handles 34 and 36 are released, and the resilience of tubular body 14 causes longitudinal edges 16 and 18 to move close to each other. Closing forces are then applied to spreader handles 34 and 36 to bring edges 16 and 18 together so that seals 50 and 52 are in sealing engagement. The locking means is actuated by continued closing pressure on the spreader handles until a point is reached where the notches 58 and 60 on locking bar 26 and notch retainer 28, respectively, are engaged by the action of biasing spring 56. Thereafter the closing forces on spreader handles 34 and 36 are released and the locking means maintains the enclosure in a closed condition.
After the enclosure is properly positioned around the joint, the interior pipe 10 adjacent the joint is pressurized by means of a high pressure test gas. Preferably, the test gas includes at least about 9% by volume helium. If the joint is gas tight, none of the pressurized test gas will leak into annular chamber 48 between the pipe joint and the enclosure. If a leak exists, then pressurizing gas including a tracer (preferably helium) will leak into annular chamber 48 and the sensing probe inserted through probe aperture 62 will detect the presence of the tracer gas by withdrawing a portion of the gas in the annular space for analysis by a spectrophotometer, or by another suitable sensing device capable of detecting and indicating the presence of the tracer gas. The withdrawn gas sample can be replaced by air which is permitted to enter the enclosure through vent aperture 64.
Another embodiment of the enclosure is illustrated in FIGS. 5-7, inclusive, which provides another form of enclosure 70 positioned about a pipe 72 and which functions in a manner similar to the embodiment of FIGS. 2-4, inclusive. Structurally, however, enclosure 70 is provided as a flexible wrap 74 that is adapted to be wrapped around pipe 72. Wrap 74 includes an inner face 76, an outer face 78, and a plurality of longitudinally spaced, arcuate stiffener members 80 positioned to provide body to the wrap so that when it is wrapped around a test section, stiffeners 80 will prevent the complete inward collapse of wrap 74 and will cause substantial inner portions thereof to be spaced from the outer periphery of pipe 72 a sufficient distance to define an enclosed chamber into which a sensing probe (not shown) can be inserted. Although shown in FIGS. 5 and 6 as positioned between inner face 76 and outer face 78, stiffeners 80 can also be positioned directly on either of those faces, if desired, so long as they are capable of spacing a portion of the wrap from the outer surface of pipe 72.
As shown in FIG. 7, wrap 74 is of generally rectangular configuration, with the major dimension thereof arranged around the outer surface of pipe 72 as shown in FIG. 5. A pair of resilient longitudinal seals 82, which can be solid or foamed rubber or plastics, is positioned at inner surface 76 parallel to and spaced inwardly of the longer edges of wrap 74, and similar seals 84 are positioned along the shorter edges thereof on both faces of the wrap to permit either shorter edge thereof to overlie the other when the wrap is installed for use.
Positioned along each of the longer edges and outwardly of each of seals 82 is a separable connecting means to permit removable engagement of portions of the longitudinal edges when the same are in overlapped condition. A suitable connecting means is a pair of cooperating strips 86 of material known as "Velcro" which on one surface consists of a series of loop-type elements, and on the opposed, engaging surface it includes a plurality of outwardly extending, hook-like elements. Similar separable connecting means 87 are provided at the edges of the wrap.
Also positioned on flexible wrap 74 and preferably at one pair of adjacent corners thereof are tabs 88 to provide a gripping means to facilitate the installation of the device around pipe 72 and to permit the respective longitudinal edges thereof to be drawn into tight engagement with the pipe outer surface to prevent dissipation of test gas by wind or other external air currents.
Suitable sheet materials for forming the flexible wrap are plastic films or other substantially gas impermeable materials, a pair of which can be sealed or otherwise joined along their marginal edges to provide inner face 76 and outer face 78 and within which stiffener members 80 can be positioned. A suitable plastic film is polyvinyl chloride. Stiffeners 80, which are of curved shape, are preferably positioned in longitudinally spaced relationship along wrap 74 and can be formed from any rigid yet resilient materials, such as sections of plastic tubing having sufficient thickness to provide rigidity. The several stiffeners can be retained in spaced pockets (not shown) formed between the inner and outer faces of the wrap. Additionally, stiffeners 80 can also be secured to the inner or outer faces of wrap 74, if desired.
The wrap of FIG. 7 is shown installed for use on a section of pipe in FIGS. 5 and 6, wherein the longitudinal edges are shown to be in peripheral contact with the outer surface of pipe 72. As in the embodiment of FIGS. 2 to 4, a sensing probe aperture 89 is provided and can be in the form of a tubular member 89 which extends from the interior surface of the wrap 74 to an outer longitudinal edge in order to provide an entry passageway for a sensing probe. If desired, a similarly configured tubular vent aperture (not shown) can also be provided, for example, on the opposite edge of wrap 74 from tubular member 89, to permit a small amount of air to enter the enclosure and replace the gas volume withdrawn by the sensing probe, thereby preventing the pressure within the enclosure from dropping below the atmospheric pressure.
Another form of test enclosure is illustrated in FIG. 8. As there shown a pair of resilient, split enclosure halves 91, 92 are secured to and carried by a pair of steel outer casings 93, 94. The enclosure halves 91, 92 function in a manner similar to the embodiments of FIGS. 2-4 and include a probe aperture 95. The steel outer casings provide increased safety for those in the vicinity of the test enclosure by laterally containing any fragments or high gas pressures that might occur in the event of rupture or other failure at the joint. Locking means similar to that illustrated in FIG. 4 can be provided on casings 93, 94 to securely lock them together.
Referring now to FIGS. 9-14, there is shown the preferred pipe testing tool of U.S. Pat. No. 4,548,069. FIG. 9 shows a portion of a well casing 110 including a junction defined by the ends of a first pipe section 112 and a second pipe section 114. Each pipe section includes an externally threaded end and the two pipe sections are interconnected by an internally threaded union 116 which is in threaded engagement therewith.
Positioned within the interior of casing 110 is a pipe testing tool 118. Tool 118 includes a lower cylindrical mandrel 120 and an upper cylindrical mandrel 122 coaxial therewith and connected thereto by means of an intermediate cylindrical spacer tube 124, which includes internal threads at each end thereof to permit a threaded connection with the respective mandrels The lowermost end of lower mandrel 120, the end opposite spacer tube 124, includes a guide plug member 126 which has a rounded end to facilitate insertion of the tool into a pipe section. Connected to the upper end of upper mandrel 122, the end opposite spacer tube 124, is a lifting cable 130 to allow the tool to be raised and lowered in order to permit it to be placed in the desired position within casing 110. Also connected to the upper end of upper mandrel 122 is a fluid conduit 134 to permit communication between the interior of tool 118 and a source of pressurized fluid (not shown).
The interior construction and interconnection of the several parts of lower mandrel 120 is illustrated in cross section in FIG. 10. As there shown, mandrel 120 is a generally tubular member and has a through bore 136 extending axially therethrough and includes means at one end for securing the guide plug 126, which also serves to close the lower portion of bore 136. Guide plug 126 can be threaded as shown and can include an internally recessed area within which a resilient 0-ring 140 can be positioned for sealing purposes. The opposite end of mandrel 120 includes a coaxial, reduced diameter piston surface 142 which terminates in an outwardly extending shoulder 144 at one end thereof and in an external thread 146 at the other end thereof Thread 146 is preferably an Acme thread, for example a 1.000-8 Acme-3G thread, for increased strength and in order to minimize the stress concentration sites which frequently exist when a thread having a V-type cross section, such as a 1.000-8UNC-2A, is utilized. A radially directed conduit 148 is provided between thread 146 and shoulder 144 to permit communication between through bore 136 and piston surface 142 Conduit 148 is spaced axially inwardly from the end of thread 146 and is preferably no closer thereto than two conduit diameters in order to minimize stress concentrations at the thread root and thereby reduce the propensity for failure at that position, which was frequently experienced when using prior art devices wherein the radial conduit was adjacent the thread end and the thread was a V-type thread.
Positioned between shoulder 144 and guide plug 126 at the lower end of mandrel 120 is a pair of opposed parallel flats 150 formed on the outer surface of mandrel 120 to facilitate the interconnection of the several parts of the assembly by providing surfaces on which a wrench or other suitable turning tool can be applied to permit engagement of threads 146 with a suitable connecting member.
A generally tubular hub member 152 is threadedly secured to the upper end of mandrel 120, opposite the end which carries plug 126, and also has a through bore 154 therein which is in axial alignment with through bore 136 in mandrel 120. Hub 152 also has a transverse threaded passageway 156 which extends radially from through bore 154 to the exterior of hub member 152. As shown, passageway 156 in hub member 152 is closed by means of a plug 158. As on mandrel 120, hub member 152 also includes a pair of opposed parallel flats 160 formed in the outer surface to facilitate interconnection. Adjacent flats 160 is an enlarged diameter portion 162 which defies an external abutment 164 at the interconnection with a reduced diameter piston surface 166. Piston surface 166 is a highly polished finished surface which includes a pair of axially spaced peripheral recesses 168 adapted to receive sealing rings, such as 0-rings (not shown). As shown, piston surface 166 does not extend beyond conduit 148.
Hub member 152 includes an enlarged inner bore 165 which is concentric with through bore 154 and which is positioned inwardly of piston surface 166. Bore 165 includes an internal Acme thread 167 which engages thread 146 on mandrel 120. Thread 167 extends only partially along bore 165 and commences at a point spaced inwardly of the end of hub 152 to provide a smooth cylindrical surface which overlies a portion of piston surface 142 of mandrel 120. Bore 165 extends inwardly to an end relief groove 169 which terminates in an inner transverse wall 171 to provide an abutment for the end of mandrel 120. End relief groove 169 is positioned intermediate the ends of enlarged diameter portion 162 and the relative sizes thereof are such that the minimum hub wall thickness therebetween is greater than the minimum hub wall thickness between piston surface 166 and thread 167 to minimize fracture failure caused by bending loads.
Slidably positioned on the outer periphery of piston surface 142 of mandrel 120 is a cylindrical sleeve 170 which is of a stepped configuration having a first cylinder 172 adapted to slidably overlie the periphery of piston surface 142 and having an overlapping cylindrical extension in the form of a second cyclinder 174 and which overlies piston surface 166 on hub 152. Positioned about the outer periphery of first cylinder 172 is a plurality of spaced annular sealing rings 176 with a plurality of intermediate spaced annular drift rings 178 positioned coaxially with the sealing rings and adjacent the respective ends thereof. Sealing rings 176 are formed from a resilient material, which can be natural or synthetic rubber, plastics, elastomers, or the like. Drift rings 178 are relatively inflexible, preferably rigid, metallic materials, so that any axial deflection in the assembly of sealing rings and drift rings is reflected solely in sealing rings 176 and not in drift rings 178.
Also positioned around piston surface 142 is a sleeve-like escape chamber 180 which abuts the side of the lowermost sealing ring and which has an inner wall 182 spaced from piston surface 142 to define an annular space within which first cylinder 172 is received One or more radial apertures 184 extends from the annular space in order to permit escape of air when first cylinder 172 is moved axially toward plug 126.
The length of second cylinder 174 of sleeve 170 is such that when the uppermost end thereof is touching abutment 164, an annular space 186 (see FIG. 12) is provided between the lower end of hub 152 and an interior land 187 of sleeve 170 and is in communication with the radially extending conduit 148.
Upper mandrel 122 is of the same construction as lower mandrel 120 and like numerals identify like parts. However, instead of plug 158 as in lower mandrel 120, hub 152 of upper mandrel 122 includes a flow constriction in radially extending passageway 156. The constriction can be in the form of a plug 188 having an aperture 190 therein, the aperture preferably having a cross-sectional area substantially smaller than that of through bore 154 in hub 152.
Spacer tube 124, providing the interconnection between the respective hubs of upper mandrel 122 and over mandrel 120, can be of any axial length desired, depending upon whether a single pipe connection joint is to be tested or whether a plurality of the some are to be tested, or even whether an entire pipe section between joints is to be tested for some particular reason. Tube 124 is a hollow cylinder having internal threads at each end adapted to engage the external threads on hubs 152. Again, an Acme thread is preferred for improved resistance to failure caused by stress concentrations.
The material from which the mandrels and hubs are preferably made is a high strength nickel-cobalt-chromium-molybdenum super-alloy designated MP35N, rather than the 4340HT and 4140HT still previously used. That super-alloy was found to provide the mechanical properties of extremely high yield strength, adequate elongation, and high fatigue resistance necessary to minimize failure of the parts subjected to tensile loading and fatigue cycling. Sleeves 170 can be made from 17-4-PH stainless steel; drift rings 178 can be made from 304 stainless steel; and plug 126 can be made from cold-rolled carbon steel.
The assembly of the testing tool is accomplished by interconnecting lower mandrel 120, as it is shown in FIG. 10, with spacer tube 124 by threading the latter thereto at hub 152, and thereafter, corresponding hub 152 of upper mandrel 122 is threadedly interconnected with the opposite end of spacer tube 124. Fluid conduit 134 is then connected to a suitable fitting (now shown) at the upper end of upper mandrel 122.
In use, assembled tool 118 is lowered into casing 110 by means of cable 130 to a point where the respective sealing rings of the upper and lower mandrels are on opposite sides of a joint, as illustrated in FIG. 9. A pressurized fluid is introduced to the interior of the tool through fluid connection 134 and through bores 136, 154 and acts through 117 conduits 148 to cause the respective sleeves 170 to move in opposite directions relative to each other, toward the respective sealing rings 176, causing compression of the sealing rings radially outward expansion thereof into sealing engagement with the interior surface of casing 110.
Because the area of aperture 190 in hub member 152 associated with upper mandrel 122 is less than that of through bores 136 and 154 in the respective mandrels and hubs the 125 initial flow of fluid is confined to the mandrels and serves to force sleeves 180 axially against their associated sealing rings. When the latter have been expanded into tight engagement with the interior surface of the pipe, the pressure within the tool increases to the point where flow of pressurizing fluid occurs through aperture 190 and enters the annular space which is defined between the upper and lower sealing ring assemblies.
Thus, it can be seen that the leak test enclosure herein described provides a rapid and secure means for enclosing a test section for confining leakage of tracer gas utilized to test for joint leakage The device does not involve the necessity for using water for detecting gas bubbles, and therefore it is usable in even the coldest weather, when freezing of water would be a problem. It also eliminates the need to periodically replenish any water which may have been lost as a result of axial movement, relative to the pipe sections, of the previously-used bubble bucket over various enlarged areas of pipe, which can cause deflection of the bucket lower seal with consequent loss of water.
As part of the present invention, it has been discovered that helium, as the tracer or test gas, either alone or in combination with another inert gas or gases, such as nitrogen, in a gas mixture containing a critical minimum level of helium, produces unexpected results in detecting previously undetectable, very small leak passages in oil field pipe, and reduces the test time for detecting somewhat larger leak passages than previously possible with prior known pressurized gas systems. Without intending to be limited, it is believed that helium is superior to prior pressurized gas systems, particularly nitrogen used in the prior systems, for the following reasons. Methane is the principal constituent of subterranean gas, which is under high pressure within the drill string. Nitrogen has a higher molecular weight and, therefore, a higher mass than methane. Thus, when nitrogen is used as the test gas for detecting leaks in a drill pipe section, the nitrogen cannot escape from very small leak passages that might otherwise allow methane to escape, and it will flow through very small but passable leak sites at a slower rate than methane. On the other hand, helium has a lower molecular weight and, therefore, a lower mass than methane, and much lower than nitrogen. Thus, it is hypothesized that helium can detect very small leak passages, smaller than those detectable by nitrogen gas, and can detect small but passable leak sites at a more rapid rate than nitrogen, because its molecular size is smaller than methane, and much smaller than nitrogen. In other words, because helium has a lower molecular weight and, therefore, a lower mass than does methane, helium should be capable of detecting all leak sites which might pass subterranean gas (essentially methane), even leak sites that would not pass nitrogen, as well as more rapidly detecting somewhat larger leak sites which are capable of passing nitrogen, but only at a slow rate. Other gases which have similar molecular weight and mass characteristics as helium with respect to methane could be used in the present invention, such as hydrogen and oxygen, if they were not otherwise objectionable. However, neither hydrogen nor oxygen can be used in accordance with the present invention because of their combustitility in the environment in which the present invention is used Helium gas possesses all of the necessary qualities for carrying out the present invention. Other gases that are also suitable include: ethane (3.0%), methane (5.0%), monochloromethane, fluorotrichloromethane, dichlorodifluoromethane, chlorotrifluoromethane, dichloromonobromomethane, monochlorodifluoromethane, sulfur hexafluoride, and propane (2.1%), among others, the parenthetical weight percentages given reflecting approximate maximum concentrations for safe operation.
Tests using a GOW-MAC Model No. 21-250 gas leak detector to measure leak rates through a given leak site have shown that the leak rate for helium is approximately 2.6 times that for nitrogen. Table I below presents the leakage rates which correspond with a given reading on a GOW-MAC detector for a given leak site:
It has been found that the speed of leak detection is related to the quantity of helium in a given volume of test gas, the greater the volume of helium, the quicker the response. And it has also been found that a particular range of mixture ratios of helium to, say, nitrogen, provides as quick a response in terms of identifying a leak site, as pure helium alone, thereby permitting such tests to be performed using a smaller amount of helium.
Specifically, tests were performed using a known leakage area and subjecting it to a test gas at a given pressure to provide a constant leak rate of the test gas through the leak site. The test gas was a mixture of helium and nitrogen. The ratio of helium to nitrogen was varied and the time for the detector to achieve the maximum reading was measured. The results of that test are presented in Table II below:
From the results presented in Table II above, it can be seen that helium to nitrogen ratios of as low as 1 part helium to 8 parts nitrogen, by volume, result in the same detection time to achieve a maximum reading on the gas detector. Ratios of 1:9 or less resulted in increased detection times to achieve the maximum reading. Additionally, in using the test gas mixtures as given above, it is preferred that the test pressure be from about 3000 psi to about 20,000 psi in order to assure detecting even the smallest leak sites within a reasonable time period.
If the time involved to detect a leak is not a critical factor, test gas having even smaller concentrations of helium can be used. The following tests were conducted to permit a determination of the minimum quantity of helium in the test gas to permit a leak to be detected using the GOW-MAC instrument.
A GOW-MAC gas leak detector (Model #21-250), which detects gases based upon their thermal conductivity as compared with that of air, and a Consolidated Electrodynamics helium mass spectrometer were used to determine the minimum helium to nitrogen operating mixtures which could be detected at a fixed pressure and leak rate. The minimum absolute helium leak rate detectable by the GOW-MAC Unit and the Consolidated Electrodynamics Unit (sold by DuPont, and henceforth referred to as the DuPont unit) was also determined.
In performing the testing, helium and nitrogen mixtures of known concentrations were pressurized up to 5500 psig and a test section of pipe was filled with the test gas mixture at that pressure. An enclosure of the type hereinbefore described was placed around the leaking test section and readings were taken from the GOW-MAC tester 30 seconds and 60 seconds after placing the enclosure around the test section. This same procedure was repeated for the DuPont unit. A fixed leak rate was set with a test gas mixture in which helium was present in an amount of 6.67% by weight with the balance being nitrogen. The leak rate was set so that concentration of helium the GOW-MAC unit displayed a scale reading of 3000 after 30 seconds. The same leak rate was used throughout the testing.
Gas mixtures of 6.7% helium and 93.3% nitrogen, by weight; 0.10% helium and 99.90% nitrogen, by weight; 0.020% helium and 99.980% nitrogen, by weight; and 0.0050% helium and 99.9950% nitrogen, by weight, were used in the tests. A calibration gas mixture including 6.65 .times. 10.sup.-7 cc-atm/sec of helium was used to calibrate the DuPont unit in order to permit a determination of the rate of helium leakage. The following equation was used to calculate the absolute helium leak rate using the DuPont unit: Absolute helium leak rate =sensitivity of the unit X reading on the meter. The sensitivity of the DuPont unit was determined during calibration. The meter was read at 30 seconds into the test. For a test mixture to be considered detectable, a minimum signal to noise ratio of 4 was selected, which means that the meter on each instrument must read 4 times the noise reading at maximum sensitivity in order for a leak to be considered detectable. The noise reading of each unit at maximum sensitivity was 5 , so that the minimum reading on each unit for detecting a leak was 20.
The following parameters were used consistently throughout the testing:
NOTE: A sniffer tube was used on the DuPont unit throughout testing,
The following tests were conducted:
The GOW-MAC unit displayed a reading after 30 seconds in Test #2 of 22. This is 10% above the minimum reading for accurately detecting a leak using that instrument and thus the Test #2 gas mixture (0.10 wt.% helium-99 wt.% nitrogen, 0.70 mol% helium-99.30 mol% nitrogen) is the lowest helium to nitrogen mixture accurately detectable by the GOW-MAC unit. The extra 10% provides a further safety factor. The minimum detectable helium leak rate under the Test #2 conditions is 1.16 .times. 10.sup.-6 cc-atm/sec helium.
Test #4 gives the minimum helium to nitrogen mixture usable with the DuPont unit and after 30 seconds of leaking, the instrument displayed a reading of 21. This is 5% over the minimum reading for a leak and is considered a further safety factor. Hence a mixture of 0.0050 wt.% helium-99.9950 wt.% nitrogen (0.035 mol% helium-99.965 mol% nitrogen) is considered the minimum helium to nitrogen mixture accurately detectable under operating conditions using the DuPont unit. The minimum detectable: helium leak rate under the Test #4 conditions is 4.62 .times. 10.sup.-9 cc-atm/sec helium. Thus, on a volumetric basis, the minimum helium to nitrogen ratio for accurate leak detection using the GOW-MAC unit is 1:142, while that using the DuPont unit is 1:2856.
While particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention, and it is intended to encompass within the appended claims all such changes and modifications that fall within the scope of the present invention.
Claims
What is claimed is:
1. A method of testing for leaks in oil field pipe at a rig floor by using a single source of pressurized test gas to actuate a testing tool positioned at a pipe test section and to pressurize the pipe test section to test for leaks, said method comprising: (a) pressurizing a test gas comprising a mixture of a detectable quantity of helium tracer gas and a carrier gas to a pressure of at least 3000 psi to provide said single source of pressurized test gas; (b) enclosing an area around the outside of the pipe to define a chamber around the pipe test section to confine a test gas therewithin; (c) actuating the test tool by introducing said pressurized test gas at a pressure of at least 3000 psi from said single source of pressurized test gas into the test tool to seal off an internal section of pipe to form a closed volume pipe test section; (d) introducing said pressurized test gas from said single source of pressurized test gas at substantially the same pressure of at least about 3000 psi as used to actuate said test tool into said pipe test section; (e) sensing the presence of leaking helium tracer gas in the chamber around the outside of the pipe test section with a sensing means; and (f) wherein the ratio of helium to carrier gas in said test gas is greater than about 1:10 by volume.
2. The method of claim 1 wherein the carrier gas is nitrogen.
3. The method of claim 1 wherein the test section is a pipe joint.
4. The method of claim 1 wherein the test gas is pressurized to its test pressure away from the rig floor by introducing a liquid under pressure into a remote tank containing the test gas.
5. A method of testing for leaks in oil field pipe at a rig floor by using a single source of pressurized test gas to actuate at testing tool positioned at a pipe test section and to pressurize the pipe test section to test for leaks, said method comprising: (a) pressurizing a test gas comprising a mixture of a detectable quantity of helium tracer gas and a carrier gas to a pressure of at least 3000 psi to provide said single source of pressurized test gas; (b) enclosing an area around the outside of the pipe to define a chamber around the test section to confine a test gas therewithin (c) actuating the test tool by introducing said pressurized test gas at a pressure of at least 3000 psi from said single source of pressurized test gas into the test tool to radially extend spaced resilient packing glands against the interior surface of the pipe on opposite sides of the area to be tested to seal off an internal section of pipe to form a closed annular volume pipe test section; (d) introducing said pressurized test gas from said single source of pressurized test gas at substantially the same pressure of at least about 3000 psi as used to actuate said test tool into said pipe test section whereby the pressurized test gas, at substantially the same pressure as used to seal off said pipe test section, occupies the annular space between the external surface of the test tool and the internal surface of the pipe test section under test between the extended spaced resilient packing glands; (e) sensing the presence of leaking helium tracer gas in the chamber around the outside of the pipe test section with a sensing means; and (f) wherein the ratio of helium to carrier gas in said test gas is greater than about 1:9 by volume.
6. An apparatus for testing for leaks in oil field pipe at a rig floor by using a single source of pressurized test gas to actuate a testing tool positioned at a pipe test section and to pressurize the pipe test section to test for leaks, said apparatus comprising: (a) means for pressurizing a test gas comprising a mixture of a detectable quantity of helium tracer gas and to carrier gas to a pressure of at least 3000 psi to provide said single source of pressurized test gas; (b) means for enclosing an area around the outside of the pipe to define a chamber around the pipe test section to confine a test gas therewithin; (c) means for actuating the test tool by introducing said pressurized test gas having a ratio of helium tracer gas to carrier gas greater than 1:9 by volume and at a pressure of at least 3000 psi from said single source of pressurized test gas into the test tool to seal off an internal section of pipe to form a closed volume pipe test section; (d) means for introducing said pressurized test gas from said single source of pressurized test gas at substantially the same ratio of helium tracer gas to carrier gas greater than 1:9 by volume and at substantially the same pressure of at least about 3000 psi as used to actuate said test tool into said pipe test section; and (e) means for sensing the presence of leaking helium tracer gas in the chamber around the outside of the pipe test section with a sensing means.
7. An apparatus for testing for leaks in oil field pipe at a rig floor by using a single source of pressurized test gas to actuate a testing tool positioned at a pipe test section and to pressurize the pipe test section to test for leaks, said apparatus comprising: (a) an accumulator; (b) means for introducing a test gas comprising a mixture of a detectable quantity of helium and a carrier gas into said accumulator; (c) pressurization means including means to introduce liquid under pressure into said accumulator to pressurize said test gas to a pressure of at least about 3000 psi to provide said single source of pressurized test gas; (d) means for remotely controlling the introduction of test gas and liquid into said accumulator and for controlling the flow of pressurized test gas from said accumulator; (e) means for enclosing an area around the outside of the pipe to define a chamber around the pipe test section to confine a test gas therewithin; (f) means for actuating the test tool by introducing said pressurized test gas at a pressure of at least 3000 psi from said single source of pressurized test gas into the test tool to seal off an internal section of pipe to form a closed volume pipe test section; (g) means for introducing said pressurized test gas from said single source of pressurized test gas at substantially the same pressure of at least about 3000 psi as used to actuate said test tool into said pipe test section; and (h) means for sensing the presence of leaking helium tracer gas in the chamber around the outside of the pipe test section with a sensing means.
8. A method of testing for leaks in oil field pipe at a rig floor by using a single source of pressurized test gas to actuate a testing tool positioned at a pipe test section and to pressurize the pipe test section to test for leaks, said method comprising: (a) introducing a test gas comprising a mixture of a detectable quantity of helium and a carrier gas into an accumulator; (b) pressurizing the test gas in the accumulator by introducing liquid under pressure into the accumulator to pressurize the test gas to a specified pressure of at least about 3000 psi to provide said single source of pressurized test gas; (c) remotely controlling the introduction of test gas and liquid into the accumulator and remotely controlling the flow of pressurized test gas from the accumulator; (d) enclosing an area around the outside of the pipe to define a chamber around the pipe test section to confine a test gas therewithin; (e) actuating the test tool by introducing said pressurized test gas at a pressure of at least 3000 psi from said single source of pressurized test gas into the test tool to seal off an internal section of pipe to form a closed volume pipe test section; (f) introducing said pressurized test gas from said single source of pressurized test gas at substantially the same pressure of at least about 3000 psi as used to actuate said test tool into said pipe test section; and (g) sensing the presence of leaking helium tracer gas in the chamber around the outside of the pipe test section with a sensing means.
9. An apparatus for testing for leaks in oil field pipe at a rig floor by using a single source of pressurized test gas to actuate a test tool positioned at a pipe test section and to pressurize the pipe test section to test for leaks, said apparatus comprising: (a) a test tool comprising a pair of spaced apart cylindrical mandrels each having a reduced diameter piston surface, each of the mandrels having a shoulder formed intermediate its length at the intersection of the reduced diameter piston surface and the full diameter portion, each of the mandrels having a through bore, each of the mandrels having a laterally extending passageway in fluid communication with the through bore of its mandrel, a pair of hub members each associated with one of the mandrels, each of the hub members being secured to one of the mandrels, each of the hub members having a through bore in fluid communication with the through bore of its associated mandrel and an external shoulder positioned radially outwardly of the mandrel, a pair of sleeves each slidably mounted on one of the mandrels adapted to abut against the shoulder of the hub member and define an annular space in communication with the laterally extending passageway, annular sealing rings positioned about the outer periphery of the sleeve, the sealing rings being positioned to abut a shoulder of the sleeve, a plug in one of the hubs having an outlet means therein adapted to be in fluid communication with the through bore of its mandrel, the hub members being secured to opposite ends of a spacer tube located between the mandrels, (b) means for pressurizing a test gas comprising a mixture of a detectable quantity of helium tracer gas and a carrier gas in a ratio of helium tracer gas to carrier gas greater than 1:9 by volume to a pressure of at least 3000 psi to provide a single source of pressurized test gas; (c) means for enclosing an area around the outside of the pipe to define a chamber around the pipe test section to confine a test gas therewithin; (d) means for actuating the test tool by introducing said pressurized test gas having a ratio of helium tracer gas to carrier gas greater than 1:9 by volume and at a pressure of at least 3000 psi from said single source of pressurized test gas into the test tool through the through bores and laterally extending passageways to cause the respective sleeves to move in opposite directions relative to each other toward the respective sealing rings causing compression of the sealing rings between the shoulder on its associated sleeve and the shoulder on its associated mandrel and radially outward expansion thereof into sealing engagement with the interior surface of the pipe to seal off an internal section of pipe to form a closed volume pipe test section; (e) means for introducing said pressurized test gas from said single source of pressurized test gas at substantially the same ratio of helium tracer gas to carrier gas greater than 1:9 by volume and at substantially the same pressure of at least about 3000 psi as used to actuate said test tool into said pipe test section by permitting the pressurized test gas, once the sealing rings are expanded into engagement with the interior surface of the pipe, to flow through the plug into an annular space defined between the sealing rings of the respective mandrels; and (f) means for sensing the presence of leaking helium tracer gas in the chamber around the outside of the pipe test section with a sensing means.
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