Closed Die Forged Bop Bonnet Housing and Method

The present invention relates generally to a high strength forged BOP (Blowout Preventer) bonnet that is created using a closed die forging technique wherein the parting line or plane is preferably formed within a flange of the BOP bonnet. This process produces a higher strength BOP bonnet due to the location of the parting line. Grain flow and material properties are optimized for superior strength of the resulting BOP bonnet.

Blowout Preventers (“BOP”) are frequently utilized in oilfield wellbore for pressure control involving shearing tubulars and closing off a wellbore. A BOP, or a BOP stack, may include a first set of rams for sealing off the wellbore and a second set of shear rams for cutting pipe such as tubing, wireline and/or intervention tools. Many different sets of rams may be utilized. BOP stacks can be quite bulky, heavy, and expensive. Due to the high pressures involved in operation, high strength metal is highly desirable.

BOP bonnets are utilized on the ends of the BOP and contain hydraulic pistons that are used during operation. BOP bonnet housings are required to contain highly pressurized hydraulic fluid. Therefore they need to be comprised of high strength material.

Examples of prior art BOP bonnets are shown in U.S. Pat. No. 10,190,382 and U.S. Pat. No. 10,378,301, which are hereby incorporated by reference. As shown in these patents it will be appreciated that BOP bonnets normally comprise a first end cap, a second end cap, a cylinder therebetween and a flange for connecting to the BOP body as shown inof the drawings herein. The end caps and central cylinder contain hydraulic actuators as shown in the patents reference above.

Machining a block of steel to create a BOP bonnet would require a great deal of time, waste a lot of material, and may not result in the high strength desired. Generally, it is more efficient that the outer shape is created first and only the insides of the bonnet housing be machined.

Casting can be used to create a BOP bonnet housing by pouring metal into a mold. However, castings often have defects. For example, if one section does not cool at the same rate, some sections may not be of the same strength. In this case, stress lines may be formed.

Forging is an ancient metalworking process that shapes and significantly hardens metal using compressive forces. This method involves heating a metal billet or ingot to a malleable state and pressing or hammering it into the required shape while the high temperature gives it the ductile feature. The temperature of the metal should be above its recrystallization point, which varies from material to material. For example, steel, as might be used with a BOP bonnet, can be forged between 1,550° F. and 2,250° F.

Closed die forging, also known as impression die forging, is a metal forming process that uses a die to force a ductile metal into a specific shape. The die is a pre-shaped forming tool that contains the negative image of the desired shape. The metal is placed on or in a die resembling a mold, which may then be attached to an anvil. Usually the hammer die is shaped as well. The hammer is then dropped on the workpiece causing the metal to flow and fill the die cavities.

The hammer die may only be in contact with the workpiece on the scale of milliseconds. Depending on the size and complexity of the part, the hammer may be dropped multiple times in quick succession.

Excess metal is squeezed out of the die cavities, forming what is referred to as flash that comes out of what is called a parting line or parting plane that is formed between the two dies. The flash cools more rapidly than the rest of the material. This cooled metal is stronger than the metal in the die, so it helps prevent more flash from forming. This also forces the metal to completely fill the die cavity. After forging, the flash is removed.

Forgings generally have about apercent higher strength-to-weight ratio compared to cast or machined parts of the same material.

Facilities that create a BOP bonnet housing shape with closed die forging techniques are not readily available. Based on information and belief only, a BOP bonnet has been made with closed die forging techniques in the past but the resulting BOP bonnet is believed not to be as strong or optimal as it could be for reasons discussed hereinafter. In light of the long felt need to contain high pressures in the BOP bonnet, there is a need to produce a higher strength BOP bonnet.

A parting line or plane is formed in closed die forging along the line or surface between the upper and lower dies. If the parting line remains straight around the periphery of the forging, it will lie in a plane corresponding to that of the mating die surfaces, which is sometimes called the forging plane.

The above prior art does not disclose a closed die BOP bonnet as described in the present specification. Consequently, those skilled in the art will appreciate the present invention that addresses the above and/or other problems.

A primary objective of the present invention is to provide an improved BOP bonnet.

Another objective of the present invention is to provide increased strength in a BOP bonnet due placement of the parting line during closed die forging.

An advantage of placement of the parting line is increased strength due to favorable grain flow.

Another advantage is that the closed die forging creates a BOP bonnet of the desired outer shape to thereby reduce the time of machining and saving raw material as compared to machining the entire BOP bonnet from a block of steel.

Another advantage is a longer movement of the material grain flow as per the elongated contours of the BOP bonnet for higher strength than prior art BOP bonnets.

Another advantage is the possibility of mass production once the upper and lower dies are made to reduce manufacturing costs.

One general aspect includes a closed die method of forging a BOP bonnet. The closed die method calls for positioning the metal to be forged between a first die and a second die. The closed die method includes moving the first die with respect to the second die toward the metal to be forged to hammer the metal to be forged repeatedly to form a first end cap, a second end cap, a cylinder between the first end cap and the second end cap, and a flange that connects to the first end cap, the second end cap, and the cylinder. The closed die method preferably also includes forming a parting line with the first die and the second die that extends through the flange.

Implementations may include one or more of the following features. The closed die method where a minimum distance between the parting line and a furthermost end of the first end cap or the second end cap is at least twelve inches. Each of the first end cap, the second end cap, and the cylinder may include rounded surfaces. A minimum distance between the parting line and a furthermost end of the first end cap or the second end cap is at least twenty inches for a larger BOP. Longer minimum distances between the parting line and a furthermost end of the first end cap or the second end cap are found in even larger BOPs, as discussed herein. In a preferred embodiment, the parting line is wholly contained inside of the flange. The flange extends outwardly from the first end cap, the second end cap, and the cylinder. In one embodiment, the present invention calls for a BOP bonnet that is forged in accord with the method discussed herein.

One general aspect includes a closed die method of forging a BOP bonnet. The closed die method includes positioning metal to be forged between a first die and a second die. The closed die method also includes moving the first die with respect to the second die toward the metal to be forged to hammer the metal to be forged repeatedly to form a first end cap, a second end cap, a cylinder between the first end cap and the second end cap, and a flange that connects to the first end cap, the second end cap, and the cylinder. The closed die method also includes forming a parting line using the first die and the second die so that the parting line is positioned at least twelve inches from a furthermost end of the first end cap or the second end cap.

Implementations may include one or more of the following features. The closed die method may include the first die and the second die forming the parting line so that the parting line extends through the flange. A minimum distance between the parting line and a furthermost end of the first end cap or the second end cap is at least twenty inches for a larger size BOP. The closed die method may include the first die and the second die forming the parting line to be completely contained within the flange. Each of the first end cap, the second end cap, and the cylinder may include rounded surfaces. The flange extends outwardly from the first end cap, the second end cap, and the cylinder.

One general aspect includes a closed die forged BOP bonnet that is formed of a forged metal using two closed dies. The closed die forged BOP bonnet includes a first end cap and a second end cap formed from the forged metal, a cylinder formed of the forged metal positioned between the first end cap and the second end cap a flange formed of the forged metal that connects with the first end cap, the second end cap and the cylinder, and a parting line formed between the two dies that extends through the flange.

Implementations may include one or more of the following features. The closed die forged BOP bonnet where a minimum distance between the parting line and a furthermost end of the first end cap or the second end cap is at least twelve inches.

Each of the first end cap, the second end cap, and the cylinder may include rounded surfaces. A minimum distance between the parting line and a furthermost end of the first end cap or the second end cap is at least twenty inches.

In one embodiment, the parting line is wholly contained inside of the flange and the flange extends outwardly from the first end cap, the second end cap, and the cylinder.

Another aspect is a method of creating a closed die forged BOP bonnet comprising positioning metal to be forged between an upper die and a lower die, moving the upper die with respect to the lower die toward the metal to be worked to hammer the metal to be worked repeatedly to form a first end cap, a second end cap, and a cylinder therebetween, and a flange that connects to the first end cap, the second end cap, and the cylinder, and forming a parting line that extends through the flange.

One general aspect includes a closed die method of forging a BOP bonnet that comprises positioning metal to be forged into the BOP bonnet between a first die and a second die. Other steps may comprise providing a parting line for the first die and the second die such that the first die may include a first die volume sufficient to contain between zero and thirty-five percent of the metal to be forged, said parting line selection also being such that the second die may include a second die volume sufficient to contain between thirty-five and one-hundred percent of the metal to be forged. The method also includes moving the first die with respect to the second die toward the metal to be forged to hammer the metal to be forged repeatedly to form a first end cap, a second end cap, a cylinder between the first end cap and the second end cap, and a flange that connects to the first end cap, the second end cap, and the cylinder.

Implementations may include one or more of the following features. The closed die method may include providing the parting line between the first die and the second die such that the first die volume is sufficient to contain between zero and twenty-five percent of the metal to be forged, the parting line also being such that the second die volume is sufficient to contain between seventy-five and one-hundred percent of the metal to be forged.

These and other objectives, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims. However, it will be understood that above-listed objectives and/or advantages of the invention are intended only as an aid in understanding aspects of the invention, are not intended to limit the invention in any way, and therefore do not form a comprehensive or restrictive list of objectives, and/or features, and/or advantages.

Detailed descriptions of the invention are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or manner.

Turning to, there is shown conceptualized closed-die forge. The metal billet, bar or workpieceto be forged is placed between the upper dieand the lower die. The lower dieis supported on the anvil. The metal workpieceis heated to a temperature at which it becomes ductile, plastic and/or moldable. The upper die, which may also be referred to as the hammer die, then hammers as indicated by arrowagainst metal workpieceto move the metal to be forged into the lower diemold, and upper die moldas indicated in dashed lines, to form the closed die forged BOP bonnetof.

The closed die forgeconfiguration may be varied. The upper dieand the lower diecould be reversed in position in forge. While hammering is the desired method to move the heated metal into the molds formed in the upper and lower dies, high pressure pressing of the dies together might also be considered.

As discussed subsequently, forming the long rounded or cylindrical shapes requires moving the metal along a considerable distance—13 to 40 inches. Forcing the metal along the rather lengthy path of the die internal is believed to create a significantly stronger final product. The forged metal would have what is sometimes referred to as a large “reduction ratio,” which is associated with stronger forges. The amount that the metal is compressed or smoothed affects the strength of the forging.

However, due to the long distances involved for material grain flow with a parting line in or near the flange of the BOP bonnet, it was not known prior to attempting the forging whether the closed die process would actually work as described herein. However it was found that the closed die process does work for this application and the results are a higher strength forged BOP bonnet.

The forging dies,may be made of high-alloy or tool steel. As is known in the prior art, the forging dies should be impact and wear-resistant, maintain strength at high temperatures, and have the ability to withstand cycles of rapid heating and cooling. It may be necessary to reheat the workpiece on occasion to continue forging to completely fill the mold in the dies.

Referring also to, the parting lineis created where the two die halves meet along the forging. The selection and location of parting line affect many parameters like load and energy requirement, grain flow, amount of draft, die sinking, trimming operation, cost of the die, defect formation, die wear and die life. The parting line is the plane where the two closed diesandmeet along the forging. The basic criteria for selection of the parting line was to cause favorable grain flow. The parting linelocation on the forging is where excess material in the form of flash (not shown) exits from the forging during the forging operation.

As mentioned previously, it is believed that one other company has made closed die forged BOP bonnets. However the parting line of that BOP bonnet, as best understood, is roughly along lineas indicated inso that two identical or roughly identical dies were used to form the BOP bonnet. In this case, there is not as much movement of the ductile metal. The “reduction ratio” is lower. Accordingly, using two roughly identical or identical dies produced a forged BOP bonnet that is believed to be not as strong as the BOP bonnet produced in accord with the current method wherein the parting line is at one side of the bonnet as indicated at.

Unlike the prior art, the parting lineis selected so that the volume within moldin dieis considerably smaller than the volume in moldin die. Depending on the selection of the parting line, moldof diemay have a volume sufficient to contain between sixty and even up to one hundred percent of the forged metal if more of the volume of the mold were moved to die.

However, in one embodiment, the dies are designed so that a parting line between the first die and the second die results in the first die comprising a first die volume sufficient to contain between zero and thirty-five percent of the metal to be forged. Accordingly, this parting line selection also results in the second die comprising a second die volume sufficient to contain between sixty-five and one-hundred percent of the metal to be forged.

In another embodiment, the dies are designed so that a parting line between the first die and the second die results in the first die comprising a first die volume sufficient to contain between zero and twenty-five percent of the metal to be forged. Accordingly, this parting line selection also results in the second die comprising a second die volume sufficient to contain between seventy-five and one-hundred percent of the metal to be forged.

In a presently preferred embodiment, the parting line (or plane)goes through the flangeand is completely contained in the flange. The flange forms an end of the end caps,and the cylinder. The metal is moved all the way down the lengthof the first and second end caps,of the BOP bonnet as well as the lengthof cylinder between the two end caps,. The greater distance of movement of the forged metal material during forging results in a stronger BOP bonnet.

The lengthfrom the parting line to the furthermost end of the end caps,as indicated by linecan be substantial. The lengthfrom the parting line to the furthermost end of the end caps in a 7″ diameter BOP is about 13½ inches. For a 13″ BOP, the length from the parting line to the end of the end caps is 21⅝ inches. In a 14⅝″ BOP, the same length is 26 inches. In a 21¼″ BOP, the length is 34 inches. In a 26¾ inch BOP, the same length is 40 inches. Thus the length from the parting line to the end of the end caps can range from greater to 12 inches up to about 40 inches.

Accordingly, movement of the metal material along this substantial distance due to hammering the metal results in very strong forged metal. This is a direct benefit from the selection of the position of the parting line to be within flange.

While the desired position of the parting line is that of being wholly contained in the flange as shown in the drawings, other embodiments could have the parting line moved above or below the flange near the flange end of the bonnet. Or perhaps a portion of the parting line might be designed to fall outside of the flange. Nonetheless, in a preferred embodiment, the parting line should be sufficiently near the flange of the bonnetso that the metal is moved a minimum distance of 12 inches for the 7″ diameter BOP, at least 20 inches for the 13″ BOP and within an inch or two of the other lengths from the parting line discussed above for the other sizes of BOPs.

Upper or hammer diecontains a negative or mirror image mold shape to that of BOP bonnetabove the parting line. This will include moldto produce the upper halfof flangeand bowlas well as internal openingin central cylinderusing plunger. Lower diehas an internal shapethat mirrors the outer shape of BOP bonnetbelow the parting line.

As discussed above, the hammer diemakes repeated strikes against the metal to be worked or forgeduntil the ductile metalmoves into the shape of the BOP bonnetwithin the molds of upper dieand lower die.

First and second end capsandare preferably mirror images of each other. While they are not technically a geometrical cylinder they are generally cylindrical at least on most sides except where they connect or meld into central cylinder. Each end cap has a rounded outer surface and is elongated with a length from 12 to 40 inches that extends from the parting line or plane. The rounded surfaces of first and second end caps,meld into the middle cylinder, which has a larger diameter than either end cap. Middle cylinderhas a cylindrical outer shape over a large surface but mates to the end caps. Middle cylinderhas rounded outer surfaces along its length. What is referred to as middle or central cylinderis also not an exact geometrical cylinder but does have generally cylindrically shaped surfaces such as rounded surfaces and a lengthand is often referred to as the middle cylinder. It will be appreciated that the diameter of central cylinderis preferably considerably larger than that of end caps,and may be up to two or three times the diameter. On the other hand, the lengthmay be shorter than the lengthfrom the parting line of the end caps and may be roughly up to at least 50%-60% or any percentage of that below 60% or the actual length.