Pressure vessel and method of welding a pressure vessel sidewall and end cap together

A pressure vessel includes: (a) a cylindrical sidewall having a wall thickness, an inside surface, an outside surface, and the cylindrical sidewall extending between a first end and a second end, wherein one of the first end or the second end includes a sidewall edge that forms part of an outwardly opening weld groove; (b) an end cap constructed to engage the cylindrical sidewall edge, the end cap comprising an end cap edge corresponding to the sidewall edge and that, when combined with the sidewall edge, forms the outwardly opening weld groove; (c) a cylindrically extending backer bar located in support of the outwardly opening weld groove formed by the sidewall edge and the end cap edge; and (d) a weld joint formed in the outwardly opening weld groove and holding the cylindrical sidewall to the end cap. A method for welding a pressure vessel sidewall and end cap together is provided.

FIELD OF THE DISCLOSURE

The present disclosure relates to a pressure vessel and to a method of welding a pressure vessel sidewall and end cap together. In particular, the pressure vessel can be a hydraulic cylinder having a piston therein and being ported for the flow of hydraulic fluid into and out of the hydraulic cylinder.

BACKGROUND

Hydraulic cylinders are typically subject to relatively large internal pressures. In order to handle these large internal pressures, the hydraulic cylinder end cap is welded to the hydraulic cylinder sidewall. Because of the high pressures experienced when using the hydraulic cylinder, it is desirable to avoid fatigue and failure of the weld joint during the useful life of the hydraulic cylinders. A common failure of hydraulic cylinders can be referred to as weld failure. Hydraulic fluid leaking from a weld joint is often a result of a weld failure. Accordingly, hydraulic cylinder designs that reduce the incidents of weld failure are desired.

SUMMARY

A pressure vessel is provided by the present disclosure. The pressure vessel includes: (a) a cylindrical sidewall having a wall thickness, an inside surface, an outside surface, and the cylindrical sidewall extending between a first end and a second end, wherein one of the first end or the second end includes a sidewall edge that forms part of an outwardly opening weld groove; (b) an end cap constructed to engage the cylindrical sidewall edge, the end cap comprising an end cap edge corresponding to the sidewall edge and that, when combined with the sidewall edge, forms the outwardly opening weld groove; (c) a cylindrically extending backer bar located in support of the outwardly opening weld groove formed by the sidewall edge and the end cap edge; and (d) a weld joint formed in the outwardly opening weld groove and holding the cylindrical sidewall to the end cap.

A method for welding a pressure vessel side wall and end cap together is provided by the present disclosure. The method includes steps of: (a) welding a sidewall edge of cylindrical sidewall to an end cap edge by introducing molten metal into an outwardly opening weld groove formed by the sidewall edge and the end cap edge, wherein: (i) the cylindrical sidewall has a wall thickness, an inside surface, an outside surface, and the cylindrical sidewall extending between a first end and a second end, wherein one of the first end or the second end includes the sidewall edge that forms part of an outwardly opening weld groove; (ii) the end cap comprises an end cap edge corresponding to the sidewall edge and that, when combined with the sidewall edge, forms the outwardly opening weld groove; and (iii) a cylindrically extending backer bar located in support of the outwardly opening weld groove formed by the sidewall edge and the end cap edge; and (b) forming a weld joint in the outwardly opening weld groove and holding the cylindrical sidewall to the end cap.

DETAILED DESCRIPTION

The following description is exemplary in nature and is in no way intended to limit the invention, its application, or uses.

An exemplary prior art hydraulic cylinder is illustrated inFIG. 1at reference number10and is provided in a sectional view. The hydraulic cylinder10includes a cylinder barrel or sidewall12, and an end cap14. Sliding within the cylinder barrel12is a piston16, and extending from the piston16is a piston rod18. The piston rod18passes through a gland20which is attached to an end of the cylinder barrel12opposite the end cap14. Attached to the piston rod18opposite the piston16is a piston rod connector22. The piston rod connector22is available for attachment to various items or tools for transmission of lineal force. An end cap connector24can be provided extending from the end cap14, and is similarly available for attachment to a desired tool for the transmission of lineal force. The piston16divides the interior25of the hydraulic cylinder10into a first region26and a second region28. Hydraulic fluid flowing into the first region26causes the piston16to move toward the gland20, and hydraulic fluid flowing into the second region28causes the piston16to move toward the end cap14. Similarly, hydraulic fluid leaves the first region26as the piston16moves toward the end cap14, and hydraulic fluid leaves the second region28as the piston16moves toward the gland20. A first hydraulic fluid line30is available for conveying hydraulic fluid to and from the first region26, and a second hydraulic fluid line32is available for conveying hydraulic fluid to and from the second region28.

The hydraulic cylinder10is illustrated with a weld groove34shown between the cylinder barrel12and the end cap14. When the hydraulic cylinder is assembled and available for operation, the groove34is filled with molten metal to form a weld joint. In the location of the weld groove34, the cylinder barrel12provides a sidewall edge36, and the end cap14provides an end cap edge38along a periphery40of the end cap14that aligns with the sidewall edge36of the cylinder barrel12. The edges36and38form the weld groove34, and the weld groove34can be characterized as outwardly opening. The outwardly opening weld groove34can be characterized as having a pointed bottom35and the edges36and38can be provided slanting away from each other from the bottom35to the outside hydraulic cylinder surface39. The weld groove bottom35includes a center42. The end cap edge38along the periphery40of the end cap14is recessed from the interior surface44of the end cap14, and the groove center42is shown located in extension over the end cap14.

During the step of welding, the weld groove14is filled with molten metal and forms a weld joint. Over time and after repeated cycles by the hydraulic cylinder10, there is a possibility that a crack may start to form along the inside of the cylinder wall12at the location of the endcap14. Continued propagation of the crack can result in failure of the hydraulic cylinder.

Now referring toFIG. 2, a hydraulic cylinder according to the present disclosure is shown at reference number60. Similar to the hydraulic cylinder10, the hydraulic cylinder60includes a cylinder barrel or sidewall62and an end cap64. Sliding within the cylinder barrel62is a piston66, and extending from the piston66is a piston rod68. The piston rod68passes through a gland70which is attached to an end of the cylinder barrel62opposite the end cap64. Attached to the piston rod68opposite the piston66is a piston rod connector72. The piston rod connector72is available for attachment to various items or tools for transmission of lineal force. An end cap connector74can be provided extending from the end cap64, and is similarly available for attachment to various items or tools for the transmission of lineal force. The piston66divides the interior75of the hydraulic cylinder60into a first region76and a second region78. Hydraulic fluid flowing into the first region76cause the piston66to move toward the gland70, and hydraulic fluid flowing into the second region78causes the piston66to move toward the end cap64. Similarly, hydraulic fluid leaves the first region76as the piston66moves toward the end cap64, and hydraulic fluid leaves the second region78as the piston66moves toward the gland70. A first hydraulic fluid line80is available for conveying hydraulic fluid to and from the first region76, and a second hydraulic fluid line82is available for conveying hydraulic fluid to and from the second region78. The hydraulic cylinder60can be referred to as “ported” because the first hydraulic fluid line80connects to the first region via port81and the second hydraulic fluid line82connects to the second region via port83.

The hydraulic cylinder60is illustrated with a weld groove84shown between the cylinder barrel62and the end cap64. When the hydraulic cylinder is assembled and available for operation, the weld groove84is filled with molten metal to form a weld joint85(shown inFIG. 3).FIG. 3is illustrated with a portion of the weld groove84free of metal, and a portion of the weld groove84filled with metal and forming a weld joint85. While the hydraulic cylinder is shown in the drawings and described, at times, without metal filling the weld groove84, this done for illustration. It should be understood that the hydraulic cylinder, when assembled for use, includes the weld groove84filled with metal as a result of welding to form the weld joint85. Exemplary techniques for filling the weld groove84or for welding in general include wire feed welding and submerged arc welding. Furthermore, once the weld groove84is filled as a result of welding, the weld joint85can be virtually indistinguishable from a remainder of the sidewall62and the end cap64. Of course, it may be possible for an experienced eye to detect the weld joint85.

Now referring toFIGS. 3-5, a portion of the hydraulic cylinder60is shown illustrating the weld groove84and the configuration resulting in the weld joint85after welding. In the location of the weld groove84, the cylinder barrel62provides a sidewall edge86, and the end cap64includes an end cap edge88. The end cap edge88is provided along a periphery90of the end cap64that aligns with the sidewall edge86of the cylinder barrel62. The sidewall edge86and the end cap edge88form the weld groove84. The weld groove84can be provided having a V shape or having a U shape. In general, the weld groove84shown can be characterized as having a U shape with outwardly opening walls. In general, a U shape is desirable to provide a wide bottom of the groove that helps create a greater area or region for filling with molten metal. In addition, outwardly slanted walls also provide the groove with a greater surface area for attachment and also a wider outwardly opening groove. The sidewall edge86and the end cap edge88can be provided as straight or chamfered (or beveled). When provided as chamfered, it is desired for the edges to be recessed. In this context, the term “recessed” means that the portion that is chamfered or beveled is chamfered or beveled in a manner that forms an outwardly opening weld groove84from the bottom to the outside surface. In other words, the recess can be characterized as a recess in the outer surface of the sidewall relative to the inside surface of the sidewall, and can be characterized as a recess in the outer surface of the end cap relative to an inner portion of the end cap. As shown inFIG. 4, the weld groove84is provided as a curved or U-shaped groove that provides a relatively wide bottom of the weld groove84. A wide bottom for the weld groove84is desirable because it creates a wider weld groove84for receipt of molten metal. The bottom of weld groove84can be referred to as the weld groove base92. The weld groove base92is relatively thin but helps contain the molten metal. Accordingly, the edges86and88are shown extending from an outside surface94of the sidewall62or the outside surface96of the end cap64, and extending in a chamfer or bevel toward legs98and99. The legs98and99form the groove base92. The center of the weld groove84along the groove base92can be referred to as the groove center100. In the case of the weld groove84shown inFIG. 5, the groove center100is at the location where the legs98and99meet. In alternative designs, the weld center is not necessarily located where the cylinder barrel62and the end cap64meet.

Beneath the weld groove84is a backer bar110. The backer bar110becomes part of the weld joint as the weld groove84is filled with molten metal and the groove base92and the backer bar110melt. Accordingly, the thickness of the groove base92should be sufficient so that it melts during the welding operation and thereby becomes welded to the backer bar110. The groove base92should not be so thick that it does not melt and does not weld to the backer bar110. The thickness of the groove base92should be sufficient to form the weld groove84and to locate the backer bar110in contact with the groove base, for example, as shown inFIG. 5. In addition, the groove base92should be sufficiently thin so that it melts along with at least a portion of the backer bar110during the step of welding to form the weld joint85. The thickness of the groove base92can be selected depending on the power of the welding process. That is, a more powerful welding process may permit a thicker groove base92. Preferably, the groove base92has a thickness of about 0.060 inch to about 0.090 inch at the location where it is intended to melt and weld to the backer bar110. The backer bar110can be provided as a continuous structure supporting the groove base92, and can be provided with an interference fit with the interior surface112of the groove base92. The interference fit can be provided as about 0.002 inch to about 0.003 inch. In addition, the backer bar110can be received within a backer bar groove120along the interior face122of the end cap64. Accordingly, the interior face122provides a backer bar groove120sufficiently deep to receive the backer bar110. The backer bar groove120can include an inside groove surface124and an outside groove surface126. The outside groove surface126corresponds to the inner surface112so that there in an interference fit with the backer bar110. The interference fit can be about 0.002 inch to about 0.003 inch.

To further help relieve the stresses on the weld joint between the side wall62and the end cap64, the groove center100can be located so that it is not directly over the end cap64. By way of comparison, the groove center42shown inFIG. 1is provided in alignment with a portion of the end cap14. In contrast, the groove center100shown inFIG. 5is located so that it is not in alignment with the end cap64. That is, the groove center100is located extending beyond the interior face122of the end cap64.