A PRESSURE VESSEL CAPABLE OF WITHSTANDING ELEVATED HYDROSTATIC PRESSURES, AND ELEVATED TEMPERATURE

Abstract: A pressure vessel capable of withstanding elevated hydrostatic pressures, and elevated temperature comprises a tubular cylindrical casing capable of withstanding extreme hydrostatic pressures having an internal cavity and a first and second opening at each end permitting access to said internal cavity. The internal cavity is divided into a first and second cylindrical plug region extending inward from the first and second opening and a hollow interior region. An optical component is in the hollow interior having at least a plurality of optical fiber pigtails extending from said optical component. A first and second cylindrical plug is force fit into first and second plug regions. At least one plug has a through-hole for receiving and passing at least some of the optical fiber pigtails to a position outside of the pressure vessel. At least one plug has a ceramic adhesive plug formed in a necked-down through-hole by inserting adhesive into the through-hole and filling substantially all of the void space within the through-hole not occupied by the optical fiber pigtails. The adhesive is allowed to encapsulate the leads or optical fibers passing through the through-hole to seal the opening. The plug has a channel machined into its outer circumference to receive an O-ring, the O-ring providing an additional seal between the plug and the tubular casing. A cap is formed to cover over and beyond the outer surface of the plug using a polymer adhesive.

Description: A PRESSURE VESSEL CAPABLE OF WITHSTANDING ELEVATED HYDROSTATIC PRESSURES, AND ELEVATED TEMPERATURE BACKGROUND OF THE PRESENT INVENTION This non-provisional application is a formalization of an earlier filed provisional application 60/221,815 filed 07/31/2000 and it claims priority therefrom. This application has identical inventors and a common assignee with the previously filed provisional application 06/221,815. The present invention relates to pressure vessels used to protect electronic or fiber optical components use in connection with fiber optic arrays such as those used in connection with down hole drilling environments in which the vessel must withstand both extremely high pressure and high temperature. Pressure vessels presently designed for Oceanographic research under conditions of high hydrostatic pressure typically employ O-ring seals. Such seals are conventionally "piston" type or "compression" type seals Such vessels have been employed to reach ocean depths such as the as the Mariana's Trench which is 36,000 feet deep. At such depths pressures of 18,000 psi must be accommodated. The present application required that the pressure vessel withstand pressures in an oil well drill hole of 10,000 psi but with the added requirement of temperatures that reached 200 degrees centigrade. The package was required to protect an optical component at these temperatures. Fiber optic leads from the components had to be protected and permitted to extend through openings in the package. At pressures as high as those required, water can wick into the interior of the pressure vessel containing the optical components to be protected. O-rings can be forced out of protected regions where gaps exist. U.S. Pat Nos. 2,547,521; 3,381,842; and 3,410,442 show packages for use in withstanding high internal pressures. Since such vessels are adapted to withstand high internal pressures, they do not provide a solution for a package that will withstand high external pressures. U.S. Pat Nos. 3,344,912; 3,358,902 and 4,226,327 show the use of heat shrinkable materials used to seal end portions of packages (e.g. food containers) or to provide an outer covering for a package. They do not teach a solution for a package that is used at extremely high pressure and temperature. BRIEF DISCRETION OF THE DRAWINGS Figure 1 is a schematic view of an interferometer; Figure 2 is a schematic view of a segment of a sonar array; Figure 3 is a schematic view of a segment of an interferometer array within a down hole monitoring hose; Figure 4 is an elevation view of a pressure vessel having a single plug; Figure 5 is a sectional view of a first embodiment of the pressure vessel of Figure 4 taken on line A- A; Figure 6 is a sectional view of a second embodiment of the pressure vessel of Figure 4 taken on line A- A; Figure 7 is a sectional view of a third embodiment of the pressure vessel of Figure 4 taken on line A- A; Figure 8 is an elevation view of a pressure vessel having a first and second plug; Figure 9 is a sectional view of a first embodiment of the pressure vessel of Figure 8 taken on line B-B showing a first and second plug and O-rings being used on each plug; Figure 10a is a sectional view of the first plug on the left of Figure 9 using an O-ring with the ceramic plug removed; Figure 10b is a sectional view of the first ceramic plug of Figure 9; Figure 1 la is a sectional view of the second plug on the right of Figure 9 using an O-ring with the ceramic plug removed; Figure 1 lb is a sectional view of the first ceramic plug of Figure 9; and Figure 12 is a sectional view of a second embodiment of the pressure vessel of Figure 8 taken on line B-B showing a first and second plug, each using first and second O-rings. DETAILED DESCRIPTION OF THE INVENΗON Figure 1 is a schematic drawing of an interferometer 2 such as a Mach Zhender interferometer, such as might be used in a hydrophone or sonar array for the detection of acoustical information. Such sensors are among the most sensitive known. Figure shows 2 shows the interferometer connected between a pair of optical couplers 4, 6 as a segment of a hydrophone array. Figure 3 shows the segment of the array positioned within a flexible tube or hose 8. The tube 8 would typically house many other segments (not shown) and might also carry a number interconnecting optical fibers, electrical conductors, optical components such as optical amplifiers. The hose 8 might be deployed in a drill hole for oil, that might be thousands of feet in length or towed behind a ship or deployed as a stationary array on the bottom of a sector of the ocean. In each such application, the optical and electronic components within the hose must be protected from extremes of hydrostatic or hydraulic pressures and in the case of down hole applications, from high temperatures approaching 200 degree centigrade. Figure 4 is an elevation view of the pressure vessel 10. The invention of Figure 4 and its alternative embodiments in the figures subsequent to figure 4 is for a pressure vessel capable of withstanding elevated hydrostatic pressures, and elevated temperature. The pressure vessel provides a protected envelope for a variety of components such as fiber optic components including item such as optical couplers, wavelength dependent multiplexers, multi-function integrated optical components, interferometers such as Mach-Zhender and Michelson types, optical sources, optical amplifiers and electronic components for signal conditioning and acquisition as the application might require. In such applications, the components are kept at atmospheric pressure. The leads, electrical or optical are sealed in a plug at the ends of the vessel. In down-hole applications, the hose or tube 8 of Figure 3 has an inside diameter that imposes a budget on the outside diameter of any pressure vessels used for components within is interior. A typical maximum diameter for a pressure vessel might be slightly less than 0.2 inches for a down hole application. Fiber optic leads or pigtails 11a and lib exit cap 12. The pressure vessel has a tubular casing 14, typically fabricated from steel that is capable of withstanding extreme hydrostatic pressures. Figure 5 is a sectional view of a first embodiment of the pressure vessel 10 taken on section line A - A of Figure 4. Figure 5 shows that the tubular casing 14 has an internal cavity 16 and with an opening 18 in at least one end. The length of the internal cavity 16 is characterized by a bracket below the internal cavity. In the embodiment of Figure 5, the opening 18 is at the left end of the tubular casing 14. The opening permits access to the internal cavity 16. The internal cavity 16 has a hollow interior identified by bracket 20, and a plug region, having a position and length identified by bracket 22. The plug region is near the opemng 18. A plug 24 is shown filing the plug region 22. Block 26 represents an electrical or optical component in the hollow interior 20. The component 20 has at least a first lead 28a, 28b passing through the plug to exit the pressure vessel as leads 1 la, 1 lb. The plug 24 is shown encapsulating, the component leads 28a, 28b as they pass through the plug region to the opening 18 and the plug 24 seals the opening 18. As shown in Figures 5 - 7, the plug 24 is cast within the plug region of the tubular casing 14 of a hard incompressible material such as a loaded epoxy resin or a ceramic adhesive. The plug is circular in cross section because the tubular casing is tubular in cross section. It should be understood, that circular cross section tubing has an advantage over other form factors at high pressure; however, if pressure and size permitted, alternative form factors could be used such as rectangular or triangular depending on the application and the requirements In the embodiments of Figures 5 and 6, the plug region has an irregular surface region identified by bracket 30 for frictionally engaging the plug. The irregular region is typically threaded, however, the surface might be improved for bonding using a chemical etch or by abrasive sanding or blasting. Figure 7 is another alternative embodiment a plug 24 is cast in the internal cavity 16 plug region 22 in which at least a portion of the plug region 22 is shown by bracket 32 as having a cross section diminishing in diameter with distance from the opening 18. The internal cross section of the internal cavity 18 is first enlarged along a first portion of the plug region 22. The plug region is then shown necked down in diameter along a second portion 32 of the plug region 22. The function of the necked down region is to drive the material of the plug into compression as the external hydrostatic pressure on the vessel increases. The dimMshing portion or necked down region prevents the plug from moving into the hollow interior 18. Shoulder 34 in Figure 6 provides a similar function. In the embodiment of Figure 7, the plug region is shown to be necked down to a diameter that is a match for the diameter of the internal cavity 14 circular cross section. In each of the embodiments, of Figures 5 - 7 and 9 - 10, the lead exiting the opening is at least a first optical fiber having an optical core covered by optical cladding. The cladding is covered by a protective plastic jacket. The jacket over the cladding is treated to remove the jacket over the desired portion using chemical or mechanical methods. The jacket is removed from a portion of the lead after leaving the component identified by phantom ellipse 36, through a portion passing through the plug to a point just below the outer surface of the plug identified by ellipse 38. The jacket is removed to permit the plug material to bond to the surface of the cladding which further perfects the hydraulic seal The cap 12 is formed from a polymer material to cover and extend beyond the external surface of the plug thereby forming a fluid barrier over the surface of the plug. Liquid Viton, a fiuorocarbon elastomer, a rubber-like material, that holds at high temperature, is applied to the top or exposed surface of the ceramic adhesive to forai. cap 12. Figure 8 is an elevation view of the pressure vessel 12 having two openings in the tubular casing 14. The openings at the left and right ends permit access to the internal cavity, the extent if which is identified by bracket 16 in Figure 9, a sectional view taken on line B -B of Figure 8. The internal cavity 16 has a hollow interior the extent of which is characterized by bracket 20. Figure 9 shows a first and second cylindrical plug 46, 48 more clearly identified in Figures 10a and 11a respectively. The first and second plugs are force fit into first and second plug regions identified in Figure 9 by brackets 40 and 42 near each of the respective openings 18a and 18b in the tubular casing 14. A component 26 is shown in the hollow interior 20. The component has at least a first lead 28a, 28b. Each plug has an outer cylindrical surface 50, 52. The respective outer cylindrical surface of each plug is force fit into the plug region opening 18a, 18b of the cylindrical casing 14a. As shown in Figures 10a and 11a, each plug 46, 48 has a through-hole 56, 58 that receives and passes at least the component first lead 28a, 28b to a position outside of the pressure vessel 10. As shown in Figures 10b and l ib, plugs 46, 48 each further comprise a first and second ceramic adhesive plug 60, 62 formed in the respective through-hole 56, 58 by inserting ceramic adhesive into the through-hole and filling substantially all of the void space within the through-hole not occupied by the lead or leads. The adhesive is allowed to encapsulate the respective lead passing through the through the respective hole 56, 58 thereby sealing the opening 18a. 18b. In alternative embodiments of Figures 10a, 10b a portion of the hole is increased in diameter and then at least a portion of the plug region has a cross section that dirninishes in diameter with distance from the opening. Referring to Figures 9 and 12, the leads 28a, 28b exiting the opening 18a, 18b are at least a first optical fiber having a plastic jacket covering the cladding. The plastic jacket of the optical fiber passing through the through-hole is treated to remove a portion of the jacket as discussed above in connection with Figures 5 - 7 and reference numbers 36, 38. Although not shown, plugs 46, 48 the embodiments of Figures 9 - 12, the through-holes 56, 58 in the plugs 46, 48 have an inner surface. A portion of each inner surface is formed to have an irregular or roughened surface region for improved bonding with the ceramic adhesive plug. The irregular surface of the through-hole is a functional equivalent to the surface in Figure 5 under bracket 30. The embodiments of Figures 9 and 12 each have an end cap 12 over the outer surface of the ceramic adhesive plug formed in the through-hole. The cap is formed from a polymer material to encapsulate the exposed cladding and to cover and extend beyond the external surface identified in Figures 10b and lib as 64, 66 of the ceramic adhesive plug thereby forming a fluid barrier over the surface of the plug. In assembling an optical component into the pressure vessel, the leads are first treated to remove the necessary jacket material. The component is then inserted into the tubular casing 14 with care exercised to insure that a sufficient strain relief is provided for the fiber optic pigtails and to ensure that the bend radiuses are sufficient to prevent unwanted evanescent radiation. This step is critical when the fiber is required to exit the component in one direction and reverse its direction v thin the pressure vessel. In an application where the pressure vessel is limited in size to under 0.2 inches, leads exiting a component might have to exit the pressure vessel at opposite ends of the vessel to avoid excessively sharp bends. . A strain relief in the optical fiber also necessary to protect the component from strain that results from the thermal expansion of the steel tubular casing over a temperature rise to 200 degrees C. The length of the fiber strain relief on the right and left sides are basically the same It is important is that the strain reliefs are sufficiently compliant, so that as .the temperature changes and the steel expands or as pressure forces contraction, the fiber is not torn out of the component. Figure 12 shows a second O-ring. The plug is extended beyond the ends of the tubular casing 14 and increased in diameter to form a cap lip that is driven against the edge of the tubular casing with increasing pressure. Figures 8 and 12 show the use of shrink tubing over the end of the lip and the tubular casing to improve the seal of the joint formed at the interface of the lip and the end of the tubular casing, with increasing pressures. Components within can be a three or four fiber coupler or even an MIOC with modulator wires. The wires could pass through the hole in the plug with the fibers. The ceramic adhesive would then be forced into the hole to fill the void space around the fibers and or wires passing through the hole to form the ceramic adhesive plug. The ceramic adhesive is slightly porous. The Viton cap seals the porous surface of the ceramic plug. As pressure is increased, the walls of the cylindrical body strain inward but the increasing pressure forces the plug into the cap forming an even tighter seal around the fibers. The component or device in the package can be immobilized by bonding it to the inner wall of the body or filling a portion of the void in the body with a Styrofoam or other material. The void is at atmospheric pressure. If the jacket can take the temperature, then the jacket is left on the fiber. If the application temperature is too high for the jacket material, then the jacket material is removed by mechanical or chemical means. The invention high-pressure vessel is the first to address the needs of the oil industries for a sensor that will withstand 10,000 psi and a temperature up to 200 degrees. No coupler produced before can meet the requirements imposed by the down-hole drilling application. Slight movement of the fibers does not change the performance of the coupler. Temperature change does change the performance of the coupler. The gases and chemicals in the hole destroy the coupler. This package protects the coupler from those materials. The package is placed in a liquid filled hose. The hose is filled with a material similar to transformer oil. The hose is armored and sealed. The oil filling the hose prevents it from collapsing. The region in the hose in which the component is positioned has a hydrostatic pressure roughly equivalent to that of the region outside of the hose. The couplers are used with sound sensors such as Mach-Zehnder or Michelson interferometers that are outside of the package, however, if protection for these components is required in alternative application, the invention package can be adapted to accommodate the requirement of the larger component. Four couplers are typically used with each interferometer. Two are used with the sensor and two more with the telemetry. When an array of sensors are used, two couplers are used with each sensor. More than one coupler can be placed in a single package if the size of the package was not limited. In the present embodiments, the diameter of the package was limited, so that only one coupler could fit into a package. If the strain relief is coiled, the radius of the bend must be large enough to prevent evanescent light from escaping through the cladding. The hose in the present application had a one-inch inside diameter hose. The outside diameter of the pressure vessel was limited to 3/16 inches. The vessel length was limited to 2 1/8 inches. The inside diameter of the body was 0.118 inches. The wall thickness was 0.035 inches. The steel used was 4130. It proved to have the strength necessary to enable the vessel to pass the deformation test at 10,000 psi. It was the strongest standard tubing that was conveniently available. The cap was made of the same material. Thermal expansion was matched to that of the tubular casing in that way. Other materials could be used but at additional expense. Any material suitable for the environment and stress could be used with the necked down; threaded hole, the ceramic adhesive and the Liquid Viton elastomer covering for the end of the exposed ceramic adhesive. The ceramic adhesive attached to the walls of the tapered hole but also to the glass cladding of the fiber. Epoxy materials would not work at 200 degrees centigrade and at 10,000 psi. The ceramic adhesive is like concrete or Portland cement. A ceramic adhesive such as that produced by Cotronics, was located at page 2498 in McMaster-Carr catalog.

Claims: CLAIMS What is Claimed Is: 1. A pressure vessel capable of withstanding elevated hydrostatic pressures, and elevated temperature comprising: a tubular casing capable of withstanding extreme hydrostatic pressures having an internal cavity and, an opening in at least one end permitting access to said internal cavity, said internal cavity having a hollow interior and a plug region near said opening, a plug in said plug region, a component in said hollow interior having at least a first lead passing through said plug to exit the pressure vessel, said plug encapsulating said component lead and sealing said opening. 2. The pressure vessel of claim 1 wherein the plug region is circular in cross section. 3. The pressure vessel of claim 1 wherein the plug region is circular in cross section, at least a portion of said plug region having a cross section diniinishing in diameter with distance from said opening. 4. The pressure vessel of claim 2 wherein the internal cavity has a circular cross section, the plug region being necked down match the internal cavity circular cross section. 5. The pressure vessel of claim 1 wherein the lead exiting the opening is at least a first optical fiber having an optical core covered by optical cladding. 6. The pressure vessel of claim 1 wherein the plug region is circular in cross section, at least a portion of said plug region having a cross section dimmishing in diameter with distance from said opening, the lead exiting the opening being at least a first optical fiber having a plastic jacket covering the cladding, a region of the plastic jacket passing through the plug being treated to remove the jacket thereby exposing the cladding, the plug being formed from adhesive encapsulating a portion of the exposed cladding. 7. The pressure vessel of claim 6 wherein the plug region has an irregular surface region for frictionally engaging said plug. 8. The pressure vessel of claim 6 wherein the plug region has an irregular surface region for frictionally engaging said plug, the irregular region being threaded. 9. The pressure vessel of claim 1 wherein the plug is formed from a ceramic adhesive. 10. The pressure vessel of claim 1 wherein the plug is formed from a ceramic adhesive, said plug having an external surface, and wherein said pressure vessel further comprises: a cap, said cap being formed from a polymer material to cover and extend beyond the external surface of said plug thereby forming a fluid barrier over the surface of the plug. 11. A pressure vessel capable of withstanding elevated hydrostatic pressures, and elevated temperature comprising: a tubular cylindrical casing capable of withstanding extreme hydrostatic pressures having an internal cavity and, an opening in at least one end permitting access to said internal cavity, said internal cavity having a hollow interior and a cylindrical plug region near said opening, a component in said hollow interior having at least a first lead, a plug in said plug region, the plug having an outer cylindrical surface, the outer cylindrical surface of the plug being force fit into the plug region opening of the cylindrical casing, the plug having a through-hole, for receiving and passing at least the component first lead to a position outside of the pressure vessel, the plug further comprising: a ceramic adhesive plug formed in the through-hole by inserting ceramic adhesive into the through-hole and filling substantially all of the oid space within the through-hole not occupied by the lead, the adhesive being allowed to encapsulate the lead passing through the through-hole, thereby sealing the opening. 12. The pressure vessel of claim 11 wherein the adhesive is a ceramic adhesive and wherein the tubular cylindrical casing and the plug are formed of steel, the plug further comprising: an O-ring positioned in a channel machined in the plug to receive the < Q-ring, the O-ring and channel being characterized to provide a seal between the outer cylindrical surface of the plug and the plug region. 13. The pressure vessel of claim 11 wherein the through-hole is circular in cross section, at least a portion of said plug region having a cross section diminishing in diameter with distance from said opening. 14. The pressure vessel of claim 12 wherein the through-hole -is circular in cross section, at least a portion of said through-hole has a cross section diminishing in diameter with distance from said opening, the lead exiting the opening being at least a first optical fiber having a plastic jacket covering the cladding, the plastic jacket of the optical fiber passing through the through-hole being treated to remove a portion of the jacket, thereby exposing the cladding, the adhesive encapsulating a portion of the exposed cladding to seal the through-hole. 15. The pressure vessel of claim 12 wherein the through-hole has an inner surface, at least a portion of the inner surface being formed to have an irregular surface region for improved bonding with the ceramic adhesive plug. 16. The pressure vessel of claim 14 wherein the ceramic adhesive plug formed in the through-hole of the plug has an outer surface and wherein said pressure vessel further comprises: a cap, said cap being formed from a polymer material to encapsulate the exposed cladding and to cover and extend beyond the external surface of said ceramic adhesive plug thereby forming a fluid barrier over the surface of the plug. 17. A pressure vessel capable of withstanding elevated hydrostatic pressures, and elevated temperature comprising: a tubular cylindrical casing capable of withstanding extreme hydrostatic pressures having an internal cavity and a first and second opening at each end permitting access to said internal cavity, said internal cavity having a hollow interior and a cylindrical plug region extending inward from said first and second opening, an optical component in said hollow interior having at least a plurality of optical fiber pigtails extending from said optical component, a first and second plug in inserted into respective first and second plug regions, each plug having an outer cylindrical surface, the outer cylindrical surface of each respective plug being force fit into its respective plug region opening of the cylindrical casing, at least one plug having a through-hole for receiving and passing at least a portion of the plurality of optical fiber pigtails to a position outside of the pressure vessel, the plug further comprising: an adhesive plug formed in the through-hole by inserting adhesive into the through-hole and filling substantially all of the void space within the through-hole not occupied by the optical fiber pigtails, the adhesive being allowed to encapsulate the optical fiber pigtails passing through the through-hole, thereby sealing the opening. 18. The pressure vessel of claim 17 wherein the tubular cylinder casing and the first and second plugs are formed of steel and wherein at least a portion of said through-hole has a cross section diminishing in diameter with distance from said opening, the optical fibers exiting the opening being at least a first and second optical fiber having a plastic jacket covering the cladding, the plastic jacket of the optical fiber passing through the through-hole being treated to remove a portion of the jacket, thereby exposing the cladding, the adhesive being a ceramic adhesive applied and hardening to encapsulate a portion of the exposed cladding to seal the through-hole. 19. The pressure vessel of claim 18 wherein the through-hole has an inner surface, at least a portion of the inner surface being formed to have an irregular surface region for improved bonding with the ceramic adhesive plug. 20. The pressure vessel of claim 18 wherein the ceramic adhesive plug formed in the through-hole of the plug has an outer surface and wherein said pressure vessel further comprises: a cap, said cap being formed from a polymer material to encapsulate a small portion of exposed cladding extending from said external surface, the cap being formed to cover and extend beyond the external surface of said ceramic adhesive plug thereby forming a fluid barrier over the surface of the plug.

Inventors: ARAB-SADEGHABADI AKBAR, CARLSON KURT R, CHERBETTCHIAN AGOP H, FREDERICK DONALD A, ARAB-SADEGHABADI, AKBAR, CARLSON, KURT, R., CHERBETTCHIAN, AGOP, H., FREDERICK, DONALD, A.
Applicants: LITTON SYSTEMS INC, LITTON SYSTEMS, INC.
Application year: 2001
Main classification: G01D11
IPC codes: G01D11, G02B6