Patent Application
20240395443
The invention is directed to pressure bulkheads for passing electrical conductors, in particular conductors connected to sensor arrays operating in high pressure environments.
In certain applications, electrical systems operate in harsh environments (e.g. high temperature, high pressure, and corrosive chemicals) and pass signals between regions of highly different pressures. There may be a need to measure the environment with sensors and it is desirable and often necessary to separate components of a system, such as electronics, from that harsh environment. In order to pass sensor signals and/or power from the harsh environment to an ambient one, a hermetically sealed bulkhead may be used.
The electrical conductors pass through the bulkhead, which seals around the conductors, while the bulkhead itself is sealed against some housing or mounting of the system to keep the internal electronics safe.
In known systems, exemplified by
The inventor has appreciated a way to hydrostatically load the bulkhead, while fully supporting the bulkhead, without inducing shear stress.
In one general aspect, a bulkhead includes a solid body having a first side and a second side, a plurality of conductors hermetically passing through the solid body, with ends of the plurality of conductors extending beyond the first and second sides of the solid body. A support substrate is formed to a) receive the solid body, b) contact the solid body on the first side, and c) pass the first of the ends of the conductors therethrough. A seal is located between the support substrate and the solid body, the seal surrounding the plurality of conductors passing through the support substrate.
Implementations may include one or more of the following features. The bulkhead may include a retainer directly or indirectly contacting the second side of the solid body and fixed to the support substrate. The bulkhead may include a biasing member between the retainer and the second side of the solid body to urge the first side of the solid body into contact with the seal. The solid body floats within a recess created between retainer and the support substrate, such that in operation, the solid body is hydrostatically loaded. The solid body may include epoxy, preferably epoxy having a tensile strength greater than 80 MPa, preferably where the epoxy has a glass transition temperature greater than 150 C. The support substrate has a recess that is wider than a width of the solid body to create a gap around the solid body. The solid body has a coefficient of thermal expansion substantially similar to or within 50% of a coefficient of thermal expansion of the support substrate. The solid body has a lap sheer strength greater than 17 MPa. The plurality of conductors may include a flex circuit, preferably having at least 50 conductors. The plurality of conductors has a circuit connector located at its first end and/or the plurality of conductors is connected to a sensor at its second end. The solid body is chemically bonded to the plurality of conductors to create a hermetic seal. The solid body is not bonded to the support substrate. The seal is located within a groove in the support substrate.
The seal contacts the solid body's first side. The first side opposes the second side. The support substrate is formed to conformably contact the solid body on the first side.
In one general aspect, a method of manufacturing a bulkhead includes providing a mold; inserting a plurality of conductors into the mold with a first end of the conductors passing through a hole in a bottom of the mold; flowing a settable material into the mold; allowing the settable material to set to form a solid body hermetically sealed to the conductors, with the first end and a second end of the plurality of conductors extending beyond opposing first and second sides of the solid body; inserting the solid body into a support substrate that is formed to a) receive the solid body, b) conformably contact the body on the first side, and c) pass one of the ends of the conductors therethrough; and locating a seal between the support substrate and the solid body's first side, the seal surrounding the plurality of conductors passing through the support substrate.
The method may provide mold release on interior surfaces of the mold prior to flowing the settable material. The material may be epoxy.
Various objects, features and advantages of the invention will be apparent from the following description of embodiments of the invention, as illustrated in the accompanying drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of various embodiments of the invention.
With reference to the accompanying figures, a pressure bulkhead for cables/conductors 15 and method of manufacturing same are disclosed. As shown in
In the details of
The body 40 is physically supported by contact between the body's bottom face 45 and housing 30 with support surface 35. As seen in
In an alternate embodiment (shown in
In operation, the high pressure 10 in the fluid acts upon the body's top side 42 and sides 47, which pressure is transferred to and supported by the bottom surface 35, which reinforces the sealing engagement. This creates a hydrostatic loading on the body, which is ideal for supporting very high pressures without creating shear, tension, or other unbalanced loads. There is no support from the recess' sides 37, and therefore no shear force is experienced to deform or damage the body 40. The body is not bonded to any metal housing, and so effectively floats within the support structure (32 and 25). As the pressure 10 increases, so does the support force and sealing quality, which is now only limited by the strength of the metal housing and compression strength of the body. In testing, the bulkhead was able to withstand pressures in environment 10 up to 140 MegaPascals (MPa), and is considered to have a working range of 80-140 Mpa, which is much higher than previously specified bulkheads.
The conductors may be bundled into many cables, preferably at least 50 insulated wires, of the type and format commonly used in industry. These may be flex cables, Ethernet, or other standard formats and may carry power and or electrical signals. After physical or chemical surface treatment, these cables are embedded in the epoxy during manufacturer to create a hermetic seal therebetween. The height of the body will determine the bonding strength to the conductors, but as there is no longitudinal force on the wires, the shear strain is minimal.
The instrument may be an industrial sensor that is inserted into high pressure corrosive environments to detect properties of the fluid and or surrounding casing, such as a pipeline or oilwell. The instrument is typically designed as a pressure vessel, having a metal housing 30 to withstand the pressure differential between the external and internal fluids. Creating a recess 32 in the wall of the housing, allows the pressure bulkhead to be assembled directly there on. Alternatively, an intermediary support structure may be used to receive the body and also sealingly engage with the housing. But that approach creates a need for an additional sealing surface.
In such tools, the sensors may include cameras, ultrasound, X ray, EMAT, calipers, pressure sensors, temperature sensors, speed of sound sensors, or magneto restrictive sensors. The cables 15 supply the power to the sensors and return the raw signals to a circuit board or connector 14.
The body and support may cooperate with one or more locating pins in order to orient the body correctly during assembly and to prevent twisting during operation.
The skilled person will appreciate that the body need not be the cylinder shape shown in preferred embodiments and could take on many shapes that cooperate with a similarly shaped void in the recess or retaining member. The body could be a sphere and the support housing could have a curved recess conforming to the bottom of the sphere and a retainer having a curved recess conforming to the top of the sphere. This would give the body two extra degrees of rotational freedom to reposition the conductors, when not under load.
Epoxies are a preferred class of materials for forming the body and can be obtained with the appropriate properties for the intended installation (max temperature, max pressure, coefficients of expansion, chemical compatibility. However, other materials may be selected by the skilled material engineer for the intended installation, preferably materials that are flowable during molding, physically strong when set, chemically resistant, temperature resistant, high bonding strength to the type of conductors used. Thus PEEK (polyether ether ketone), glass, ceramics, epoxies, and plastics are good choices.
The epoxy may be one of several compounds used in industry that can withstand the temperatures and corrosive environment expected. The following are examples of properties that may be used to select an epoxy for a given application: A) the epoxy should have a bond strength strong enough to withstand the shearing stress exerted on the feedthrough by the external pressure; B) the epoxy should have a glass transition temperature above the operating temperature of the bulkhead, so that the epoxy does not flow into the low-pressure side 20 when pressurized; C) the epoxy should have a thermal expansion coefficient as close as possible to the retainer 25 and/or recess 32, preferably within 50%, in order to minimize the stresses induced in the epoxy; D) epoxy having a tensile strength greater than 12 ksi, preferably wherein the epoxy has a glass transition temperature greater than 150° C.; or E) the epoxy has a lap sheer strength greater than 17 MPa.
Examples of suitable epoxies include Masterbond EP15 which exhibits a tensile strength of 80 MPa, a thermal expansion coefficient of 22 ppm/° C., and an operating temperature up to 121° C.; and Aremco 2220 which has a flexural shear strength of 110 MPa, a thermal expansion coefficient of 32 ppm, and an operating temperature up to 204° C. Some epoxies are preferably cured at an elevated temperature and pressure. Degassing the epoxy under vacuum additionally ensures that there are no voids in the uncured epoxy added to the mold. The cured body may be tested for internal flaws and cracks by applying oil and vacuum.
