Patent Description:
This invention was made with Government support under Contract No. DE-NE0000633 awarded by the Department of Energy. The Government has certain rights in this invention.

This disclosure generally relates to a raised face flange system, and some embodiments relate to a vessel of a nuclear reactor module comprising a vessel flange joint including such a raised face flange system, as set out in the appended claims.

Piping may include piping flanges to provide a leak-free coupling between two pipe segments. <FIG> illustrates a cross section of piping including a pipe segment <NUM> having a flat face flange formed thereon to mate with a flat face flange formed on a pipe segment <NUM>. The flat face flanges may include bolt openings <NUM> to receive bolts that may be tightened to form a leak-free joint (in some examples, using a ring gasket <NUM>).

As illustrated by <FIG>, which shows an end view of the flat face flange of the pipe segment <NUM>, the bolt openings may surround the piping. The required bolt tension for each bolt to avoid a leak may be based on a quantity of the bolts and internal pressure in the piping.

<CIT> discloses a flanged joint for e.g. a connection between pipes carrying high-pressure fluid, in which there are two pairs of mating joint faces <NUM> and <NUM> at radially inner and outer positions respectively on opposing flange faces. Fastening means <NUM> pass through a clearance <NUM>. There is a small axial difference between a radial plane including the inner mating faces and a radial plane including the outer mating faces, so that when the joint is initially assembled as in <FIG>, a small gap remains at <NUM>. This gap is closed when the fastening means are correctly tightened. The improved joint is resistant to a) overstressing during tightening; b) axial tension; and c) external bending stress.

The invention is defined as set out in the appended claims.

The included drawings are for illustrative purposes and serve to provide examples of possible structures and operations for the disclosed inventive system. These drawings in no way limit any changes in form and detail that may be made by one skilled in the art without departing from the scope of the claimed invention.

Some flanges used for reactor pressure vessels (RPVs) or containment vessels in nuclear reactor modules may resemble a configuration similar to piping flanges, except that the diameters are much larger. Depending on the pressure load of the vessel, the required bolt tension for each bolt to avoid a leak may be too high for commercially available tensioning tools for some known flanges (such as the flat face flange or some known raised face flanges). Even for pressure loads where commercially available tensioning tools can be used, the required flange/bolt dimensions may require large quantities of raw materials (e.g., steel), great expense to manufacture/assembly, and/or may require an undesirably large footprint for the nuclear reactor module.

For some vessels, one way to control leaks may be to select an appropriate number and size of bolts to resist the pressure load of the vessel. However, in some nuclear reactor modules, due to the offset between the centerline of the adjoining vessel shells and the flange, a large amount of rotation (e.g., prying) may occur. This rotation may lead to leaks unless the flange is stabilized.

To minimize flange rotation for avoiding leaky joints, bolt tension may be increased. However, the amount of bolt tension needed in some nuclear reactor modules for known flat face or raised face flange configurations may be too high for commercially available tools. Developing custom bolt tensioning tools and processes may require significant capital investment, testing and prototype.

The invention described herein includes a dual raised face self-energizing vessel closure flange for a nuclear reactor module. This flange may include two raised faces to generate a mechanical lever action between the contact faces and bolt axes. The two raised faces may be offset by a small amount to de-energize the vessel shell during both bolt tensioning and to energize the seal surface(s). The de-energized shell may deform during application of pressure to less extent than in other nuclear reactor modules, which may stabilize the joint against rotation and prying. This configuration may allow the bolt loads to be reduced significantly to a range where commercially available bolt tensioning tools may be used.

The reduced bolt loads may lead to a more compact design - the flange may be smaller than flanges used in known nuclear reactor modules for a given pressure load. For instance, while a dimension of a flat face flange may be required to be the same length as a diameter of a vessel for a given pressure load (to provide a flat face surface of the same length), this dimension may be reduced for the same pressure load by using raised face flanges, and still further reduced by providing the offset for the same pressure load - providing an overall more compact flange for the given pressure load. <FIG> illustrate a vessel flange joint that may be used in an RPV and/or containment vessel. The vessel flange joint may utilize any compact raised face flange assembly described herein.

Also, since any application in which a leak tight flange is needed may benefit from a more compact flange (e.g., reduced material costs), any compact raised face flange described herein may be used in any environment in which a leak tight flange is needed, such as marine environments, piping, fluid (e.g., liquids or gasses) storage vessels, etc., even where the scale of dimensions may be completely different than a nuclear reactor vessel.

<FIG> illustrates a cross-sectional view of a compact raised face flange system <NUM> using a dual raised face, according to the invention. The assembly <NUM> includes a raised face flange <NUM> (e.g., an upper flange or a lower flange) formed on a sidewall <NUM> of a shell (e.g., an upper sidewall or a lower sidewall) and a mating flange <NUM> (e.g., the other of the upper flange or the lower flange) formed on the sidewall <NUM> of the shell (e.g., the other of the upper shell or the lower shell). The assembly <NUM> includes a bolt <NUM> (and associated bolt fasteners, not shown) to apply tension to hold the flanges <NUM> and <NUM> together to form a seal. The bolt <NUM> compresses a gasket (not shown) located between the flanges <NUM> and <NUM> to form the seal.

The raised face flange <NUM> includes a bolting circle face <NUM> defining an opening for the bolt <NUM> and a pair of offset raised faces. The pair of offset raised faces includes an inner diameter raised face <NUM> that is offset with respect to an outer diameter raised face <NUM>. In particular, a distance between the plane of the outer diameter raised face <NUM> and the plane of the bolting circle face <NUM> is greater than a distance between the plane of the inner diameter raised face <NUM> and the plane of the bolting circle face <NUM> to maintain the seal.

The pair of raised faces may include any seal feature used in any known flanges. The inner diameter raised face <NUM> includes one or more grooves to receive one or more ring gaskets, respectively. An exposed portion of the inner diameter raised face <NUM> makes contact with a corresponding surface of the mating flange (e.g., the seal feature may be located within a channel formed in one or both of the surfaces).

In this example, in accordance with the invention, the surfaces of the pair of offset raised faces are entirely in parallel planes (e.g., both surfaces are flat and have no slope), which may reduce machining complexity. In other examples depending on machining options available, the surface of the inner diameter raised face <NUM> may be sloped with a thinner section closer to the bolt opening. The slope may be a linear slope or a non-linear slope along the entire surface of the inner diameter raised face <NUM>. A sloped surface in which the thinner section is closer to the bolt opening may further distribute pressure along the surface of the inner diameter raised face (e.g., compensate for a "fish mouth" prying caused by more force on an area of the surface closest to the bolt opening). In an example not in accordance with the invention, in the case of a linear slope, the entire surface of the inner diameter raised face <NUM> may be located in a plane that is intersecting with a plane in which the surface of the outer diameter raised face <NUM> is located. In accordance with the invention, the outer diameter raised face <NUM> may also include a slope, and this slope corresponds to an inner diameter raised face slope (e.g., simultaneous sloping).

For the purpose of emphasis, the offset in the illustration is not to scale. In some nuclear reactor module applications, the offset may be approximately <NUM> mils (e.g., the outer diameter raised face <NUM> may be approximately <NUM> mils thicker, say <NUM>-<NUM> mils thicker, than the inner diameter raised face). In other applications in which the compact raised face flange assembly <NUM> is smaller or larger, the offset may also be smaller or larger. A thickness of the offset may be selected based on a deformability of vessel sidewalls (e.g., a pipe sidewall), a flexibility of the body of the raised face flange, required bolt tension, distance between the pair of offset raised faces, or any other characteristic of the pressure device (e.g., a vessel, a pipe, a hull, a hatch, or the like, or combinations thereof) and/or the raised face flange assembly <NUM>.

In the illustrated example, the mating flange <NUM> includes a flat face. In other examples, it may be possible and practical to use a difference surface on the mating flange <NUM>. For instance, it may be possible and practical to include raised faces on the mating flange <NUM> (and raised faces on the mating flange <NUM> may or may not include any offset depending on how much offset is included for the pair of raised faces of the raised face flange <NUM>).

The raised face flange assembly <NUM> may be used with any pressure device (e.g., vessel) described herein. For example, in an example in which the raised face flange assembly <NUM> is used for a vessel similar to the vessel shown in <FIG>, the faces <NUM>, <NUM>, and <NUM> and the one or more grooves <NUM> may form a continuous ring shape. The bolting circle face <NUM> may include any number of bolt openings for any number of bolts <NUM> to surround the vessel. As described herein, bolt tension for each bolt may be less than the bolt tension used in some known vessel flange joints. As a result, bolts may be smaller, and dimensions of the flange may also be smaller. Accordingly, the flange may protrude less from the vessel than a vessel flange joint based on known flanges - reducing the overall footprint of a nuclear reactor module.

Any feature of the raised face flange <NUM> or any other flange described herein may be used in a blind flange, vessel nozzle covers, bolted valves, bonnets of a valve, or the like. In some examples, a blind flange, vessel nozzle covers, bolted valves, bonnets of a valve, or the like, may include a dual raised face similar to the dual raised face of raised face flange <NUM>.

<FIG> illustrates internal forces acting on a compact raised face flange assembly <NUM> under internal pressure in the vessel, according to various embodiments. The compact raised face flange assembly <NUM> may be similar to any compact raised face flange assembly described herein, such as compact raised face flange assembly <NUM> (<FIG>). The internal forces may include a contact force <NUM> associated with the inner diameter raised face <NUM>, a contact force <NUM> associated with the outer diameter raised face <NUM>, an endcap pressure force <NUM> in the vessel shell, and bolt tension <NUM>.

Prying may be primarily caused by the endcap pressure force <NUM> because this force <NUM> may be offset from a center of the bolt. This lever action and rotation of the flange may be exacerbated by the flexibility of the flange itself (given that the flange has a finite thickness / rigidity). The rotation of the flange may be controlled by the geometric distances of the lever arms (L<NUM> and L<NUM> in addition to the flange thickness) and the magnitude of the forces in the flange system.

While equilibrium of the system may be maintained by the internal forces, that alone does not ensure a leak-tight joint. In order to prevent leakage through the flange, the contact at the seal surfaces may be maintained below the springback of the seal. By increasing bolt tension, the contact force at the inner diameter of the flange may be maintained at the seals. However, this may require a large magnitude of bolt load.

In order to stabilize the joint rotation, a small offset between the two raised faces of the flange may be introduced such that the thickness of the outer diameter may be slightly larger than the thickness of the inner diameter. <FIG> is a heat map indicative of internal force distribution in a raised face flange with no offset between raised faces, and <FIG> is a heat map indicative of internal force distribution in a raised face flange with the small offset. <FIG> and <FIG> show the relative stress distribution of the flange when the same bolt load is applied with (<FIG>) and without (<FIG>) the small offset.

The effect of the small offset of the pair of raised faces manifests itself in two observations. First, the contact stress distribution <NUM> at the seal grooves shows a more uniformed and concentrated distribution with the small offset included. The better contact force may ensure a leak tight seal arrangement. Second, when the small offset is included, vessel shell stresses <NUM> may be reduced in the vicinity of the transition region from the flange to the vessel shell. As a result, more of the bolt tension strain energy may be utilized to keep the joint tight as the vessel shell is de-energized (e.g., not deforming). This feature may be referred to as the self-energizing characteristics of the small offset on the seal joint. The bolt load necessary to keep the joint leak tight may be reduced by over <NUM>-<NUM>%, which in some nuclear reactor modules may allow the use of commercially available equipment.

Any compact raised face flange described herein may be formed by forging, e.g., forging a vessel shell having a compact raised face flange formed thereon. In other examples, it may be possible and practical to mill one raised face following forging to, say, form a linear slope or a non-linear slope. <FIG> illustrates a cross-sectional of a compact raised face flange assembly <NUM> with a linearly sloped inner raised face, according to an example which is not in accordance with the invention but which is useful to the disclosure. A non-linear slope may have a curved profile that may be based on an expected bowing of the flange (e.g., the curve profile may match a curve profile of an expected deformation of the bolting circle face for a given bolt tension / vessel shell rigidity). As mentioned previously, in accordance with the invention, it may be beneficial to provide a slope on the outer raised face as well, corresponding to a slope of an inner raised face.

In the illustrated examples, a vessel of a nuclear reactor vessel may resemble two pipes. However, any compact raised face flange described herein may be used in other scenarios. For instance, some nuclear reactor vessels may include a cylindrical vessel and a hemi-spherical head to provide a more direct and advantageous load path for the internal pressure to react on, and any compact raised face flange described herein, of course, may be utilized with these nuclear reactor vessels. Also, in some applications, a pressure device on which any compact raised face flange described herein may be utilized may be any other shape (not necessarily including any sidewall resembling a pipe).

References have been made to accompanying drawings, which form a part of the disclosure and in which are shown, by way of illustration, specific implementations. Although these disclosed implementations are described in sufficient detail to enable one skilled in the art to practice the implementations, it is to be understood that these examples are not limiting, such that other implementations may be used and changes may be made to the disclosed implementations without departing from the scope of the appended claims.

Claim 1:
A raised face flange system (<NUM>), comprising:
a first, raised face flange (<NUM>) having:
a bolting face (<NUM>) defining one or more openings for one or more bolts, respectively; and
a pair of raised faces (<NUM>, <NUM>) including a first raised face disposed in a first plane and a second raised face to form a seal in a nuclear reactor module, the second raised face disposed in a second plane that is different than the first plane, the first raised face having one or more grooves (<NUM>) positioned to receive a gasket;
one or more ring gaskets positioned in the corresponding one or more grooves;
a second flange (<NUM>); and
a bolt (<NUM>) extending through the first flange and the second flange in series;
wherein the bolting face (<NUM>) is disposed between the raised faces (<NUM>, <NUM>) in a third plane that is different than the first and second planes;
wherein the bolting face and the raised faces face in one direction; and
characterised in that the distance between the second plane and the third plane is greater than the distance between the first plane and the third plane to distribute contact force with a mating flange over the area of the second raised face to maintain the seal.