GB2155391A - Method of manufacturing a chemical heater - Google Patents

Abstract

In the preferred embodiment, the chemical heater incorporates an encircling bottom support (24) having a centralized upstanding neck (28) extending therefrom. A combustible solid fuel compound (42) is molded about the upstanding neck. A deflector plate (44) is provided to deflect hot gases jetting outwardly from combustion of the sold fuel compound against the wall of a pipe (12) to be heated. The heater is prepared from a cement by casting in an appropriately shaped mould, curing the mixture in the mould under water, removing the casting from the mould, air drying and then curing at approx 300 DEG F. After cooling, the casting is packed with a solid fuel compound and then heated again at approx. 300 DEG F. <IMAGE>

Description

SPECIFICATION Method of manufacturing a chemical heater Background of the disclosure In drilling an oil well, especially at an offshore location, it is necessary to install wellheads of various sizes of large diameter pipe. Consider, as an example, the instance where several sizes of casing are installed in a well. The well might include, as an example, a 36 inch drive pipe. There may also be a 20 inch casing, 13 3/8ths inch casing and 9 5/8ths inch casing. It is necessary to install a termination wellhead at every change of size. The wellhead is typically installed by first cutting the casing, preheating the casing and then welding the wellhead in place. The wellhead is necessary to mount other equipment or to otherwise install the next casing string.Often, this requires cutting a very thick wall casing, even in the range of 11/2 inch thick and thereafter making a multi-pass welded bead to attach the well head. This requires a tremendous amount of preheating to obtain a quality weld.

For drilling rigs located at sea, preheating is something of a problem. In inclement weather, wind shields must be installed and a number of welders will position their torches on the casing and wellhead to preheat it for perhaps 4 to 6 inches below the casing head in length to perhaps 500 F. This is difficult and time consuming. Moreover, cooling beings on the instant that preheating is stopped. It is difficult to preheat the casing and simultaneously weld a wellhead to it.

Certain devices have been provided heretofore to serve as preheaters. While these devices have various and sundry advantages, it is believed that the device of this disclosure is much more attractive for the intended purpose, namely to provide a chemical heater which can be selectively installed within a casing, whereby preheating occurs from the interior. This enables the welder to install the wellhead and quickly begin the multi-pass bead required to fasten it in place.

The various preheater devices are typified by the patent of Jaeger, Patent No. 3,082,760. However, this device and others like it are believed to be limited. There is a real risk that the preheater device will be lost down the casing. If this occurs, it may then be lost in the wellbore, and thus poses a serious problem. It is necessary to remove it because it is very difficult to drill through the steel Jaeger device. In either case it is not very desirable.

The preheater device of this disclosure utilizes a cement receptacle which is non-corrosive to saltwater, relatively inexpensive, and able to be broken into small pieces should it fall into the weilbore. It is relatively easy to drill through the cement device. This does not impede the drilling process that occurs subsequently to the use of the preheater device. The preheater device is not re-usable and is discarded after it has been used.

The present disclosure is therefore directed to a chemical heater which is formed of a cement body of frangible material. This includes a bottom cylindrical receptacle. It terminates at the center in an upstanding stalk with light weight wire pre-cast through the length of the body. The cement body is self-centralizing and supports an elongate cast cylindrical exothermic compound. One suitable material is molded thermite. A deflector plate made of the same cement is positioned on the top. It is sized relative to the casing to direct the flow of hot gases outwardly and against the wall of the casing to be heated. The device is held in place by a light duty, heat shielded chain attached to one of the utility hoist cables common to all drilling rigs.

Brief description of the drawings So that the manner in which the above recited features, advantages and objects of the invention, as well as others, which will become apparent, are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate only typical embodiments of the invention and are not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

Figure 1 is a partial sectional view through the chemical heater of the present disclosure positioned in a casing to heat the casing and wellhead for welding.

Detailed description of the preferred embodiment Attention is first directed to the single view which discloses the apparatus of the present disclosure. It is identified generally by the numeral 10. It is shown in a pipe 12. Assume, for purposes of illustration, that the pipe 12 is a large casing having a wall thickness conforming with industry standards. The pipe 12 can range from 1/2 inch thick to about 1 1/2 inches or greater. Moreover, a well head 14 is to be attached to the pipe 12.

The wellhead 14 is constructed with an internal shoulder 16to abut the end of the pipe 12. It has a cylindrical portion 18 which telescopes over the pipe. A multi-pass bead is formed at 20, and an inside or finish bead is formed at 22. The bead 20 must be formed first to fully and completely anchor the wellhead to the pipe 12.

The weld 20 is a high quality weld, subject to 100% inspection, and must be formed in many passes.

It is very important to preheat the pipe to a specified temperature. Failure to evenly preheat the pipe may damage the welds 20 and 22. It is for this purpose that the present chemical heater is installed in the pipe 12.

Moreover, it is spaced so that the rising hot gases in the pipe are deflected against the pipe in the near vicinity of the welds 20 and 22 to preheat a narrow welding zone to the required temperature. Since it requires a substantial period of time to weld the wellhead in place, the heater of this disclosure releases heat for a significant interval. This is a scale factor which can be varied dependent on the size of the pipe, the temperature required in preheating, the number of passes required in the welds 20 and 22 and other factors such as these. Suffice it to say, the present disclosure provides a heater which can be sized to preheat the pipe to the required temperature for the required interval. To this end, the device 10 is shown in the pipe 12, being located in the position that it maintains during use.

The chemical heater device 10 includes a cement support member 24. This is constructed in the form of a cylinder with centralizing projections. The member 24 is fabricated of a heat resistant calcium aluminate cement mixture including expanded perlite, a siliceous volcanic rock, and is capable of supporting the combustible element during its combustion, as for instance, at temperatures upwards of 5,000cm. The support member 24 is of sufficient thickness to retain the white hot slag from the exothermic reaction.

Ideally, it is quite frangible and can be easily fractured on drilling through it later in the process should it all fall into the weilbore. There is an air gap 26 at the top ofthe cylinderto direct hot gases at the casing wall 12.

A smaller diameter cellulose tube 29 fits over the neck 28 of the device and is filled with a high heat refractory cement shield to protect the slender neck 28 from the high temperatures generated by the fuel 42.

Large heaters 10 with correspondingly large necks do not require a protective tube or the refractory shield.

Ideally, the neck 28 is cast as a single piece with the bottom support member 24.

The heater 10 is centralized within the pipe 12 by several integrally cast protrusions 30. A light weight wire 32 is cast into the device as a means of reinforcing the neck 28. The wire 32 protrudes from the top of the neck 28 forming an eyelet 31. It will be recalled that the heater is partly combusted and, therefore, looses weight during combustion. It is preferable that the wire 32 be sufficiently strong even when heated that it retains its strength during the burning of the fuel. A light duty support chain, heat shielded with woven fiberglass tubing, is attached to the reinforcing wire, at the eyelet 31 to allow attachment of the device to the available utility hoist cable common to all drilling rigs.

The numeral 44 identifies a top deflector plate. The deflector plate is supported on an inclined circumferential shoulder 46 formed on the neck 28 of the device 10. The angle of the shoulder 46 need not be extreme, and is typically in the range of 45 to 60 degrees. The deflector plate 44 is provided with a matching counter-sunk shoulder for cooperative engagement with the shoulder 46. The deflector 44 terminates at an outer edge which is sized to fit within the casing 12 with perhaps 1/4 to 1/2 inch of clearance. During combustion, rising hot gases jet outwardly through the gap 26 defined by the deflector 44 and the top of the cylinder support 24, and flow past the edge of the deflector 44. This deflects the hot gases towards the wall and thereby heats the pipe 12 in the most desirable manner.The deflector 44 assists in directing the heat against the casing 12 in the near vicinity of the weld bead 20 on the exterior and the weld head 22 on the interior of the casing. The device is positioned so that the edge of the deflector 44 is closed to the bead 22 so that the hot gases are deflected against it.

The device attendant the invention is formed by first preparing the molds for casting of the heater 10. The molds are greased with non-watersoluable heavy grease and sprayed with a releasing agent. The neck reinforcing wire 32 is then placed in the neck of the mold. The molds are then set up in curing tanks.

The cement mixture is formed by blending the dry ingredients comprising the mixture until well blended.

As an example, the following ingredients and proportions are used to make a quantity of cement mixture. It is understood that this is an example for illustrative purposes only and that more or less cement mixture may be produced by varying the quantities of the the ingredients while maintaining the ratio of ingredients in the mixture. For this example, the cement mixture comprises the following ingredients and proportions: Calcium aluminate cement 50 Ibs.

Fine grained sand 33 Ibs Expanded perlite 3 qts.

Wire, fibre and plastic 1,000 grams Water and ice 2.5 gals.

The dry ingredients are first mixed until well-blended. Water and ice is then added to the mixture, which mixture is mixed for approximately 4 minutes, sufficiently wetting the dry ingredients and forming a pourable cement mixture.

The cement mixture is poured into the mould by first filling the neck of the mold. Additional reinforcement wires 33 may be added as the neck is filled to strengthen the neck base of the heater 10. The mold is slowly filled to avoid air bubble entrapment. After the mold is completely filled, it is covered with water for curing.

The cement cures under water for approximately twenty-four hours.

After the cement has cured, the casting is removed and air dried. A one-quarter inch heat shield of refractory cement 37 is installed around the neck and on the interior floor of the casting prior to air-drying for twenty-four hours. The casting is then cured in an oven at 300so. for a minimum of twenty-four hours. After curing in the oven, the casting is removed and allowed to cool.

The fuel 42 is a sacrificial, poured mixture made of non-toxic materials. One example is exothermic thermite which is defined, for purposes of this disclosure, as a granulated and cast mixture of aluminum particles with iron oxide. A bonding agent is added and suitable bonding agents include various and sundry binders such as starch. The fuel 42 is sacrificial in that it must be a combustible material which sustains a slow burn for the requisite interval. For instance, the fuel may be poured with suitable inhibitors and binding agents so that it burns at 5,0003F for sufficient time to heat the casing by convection and subsequently the welihead by conduction. It will be appreciated that the fuel compound 42 shrinks during combustion however, it maintains its molded shape and does not liquefy.As it shrinks, it nevertheless gives off great jets of heated gases which rise towards the deflector 44 and jet through the gap 26. This preheats the pipe to the required temperature for the required interval. Various and sundry inhibitors, as for example perlite, may be added to slow down the rate of burning.

As an example, the following ingredients and proportions are used to make a quantity of fuel compound. It is understood that this is an example for illustrative purposes only and that more or less fuel compound may be produced by varying the quantities of the ingredients while maintaining the ratio of ingredients in the compound.

For this example, the fuel compound 42 comprises the following ingredients and proportions: Iron oxide 110.0 Ibs.

Aluminum 40.8 Ibs.

Starch 16.5 Ibs.

Perlite 13.0 Ibs.

Hydroxal methyl cellulose 600 grams The dry fuel ingredients are mixed with methanol at a ratio of 0.5 cup measure of methanol per kilo of dry fuel. The dry fuel and methanol are blended to a doughy consistency and packed in the casting. The fuel mixture is tamped down uniformly until the casting is filled.

The fuel compound 42 is topped off with a quick-start mix comprising the following ingredients and proportions: Iron oxide 64.0 Ibs.

Aluminum 23.0 Ibs.

Hydroxol methyl celullose 400 grams The dry ingredients of the quick-start mix are mixed with methanol at a ratio of 0.75 cup measure of methanol per kilo of dry quick-start mix. Approximately 250 grams to 500 grams, as required, of the quick-start mix is used to top off the fuel compound 42. The cardboard fuel riser tube 27 is notched about the periphery thereof at 31 providing immediate and uniform venting of gases under the deflector plate 44 at ignition. The heater 10 is then cured in an oven for at leasttwenty4our hours. The heater 10 is completely cured when all volatiles are driven off. The heater 10 is then removed from the oven and allowed to cool prior to painting and preparation for shipping.

The device of the present invention is particularly easy to use. It is suspended in the casing 12 so that the deflecting plate 44 is positioned adjacent to the casing cut-off at 16. The heater 10 is lowered into the casing until it is positioned as shown in Figure 1. The welder then ignites the fuel through the touch-holes 47 located in deflector plate 44 with his torch. Various and sundry temperature sensitive devices are used on the exterior to determine that the casing has been adequately preheated. When this occurs, usually within 5-8 minutes, the welder can then begin welding the welihead in position by forming the multi-pass bead 20. On large casing, the bead 20 is formed by many passes. After the several passes are made, the bead can thereafter be inspected on permitting the casing to cool. It is also necessary to form the bead 22 on the interior of the casing.This bead is formed typically after the heater 10 has been removed from the casing.

However, for continued heating of the casing, the heater 10 may be lowered slightly and remain in the casing while the bead 22 is formed.

The present apparatus can be sized by varying the amount of exothermic compound placed into the cement casting. For a given combustible mixture such as thermite, the dimensions can be varied to control the duration of burning.

The heater 10 may also be used for postheating the casing and welihead member. It is desirable to postheat the pipe 12 and wellhead 14 to remove the brittle areas in the heat affected zones. A postheat temperature of 1,050 -1,100 F is desirable. After initial combustion the fuel compound 42 continues to generate heat to maintain the pipe at a welding temperature. Often times, however, forming the weld beads may require several hours. A second heater 10 may thus be required to insure that the casing and wellhead member do not cool too rapidly. Rapid cooling must be avoided.To assure slow cooling, a second heater 10 is positioned in the casing after the weld beads have been completed and burned to raise the casing is then capped and the wells protected by wrapping a blanket of asbestos or other suitable insulating material about the casing. The welded area is thus permitted to slowly cool at a uniform rate substantially reducing the risk of stress fractures and separation of the pipe 12 from the wellhead 14.

The integrally cast projections which extend from the bottom and upper third of the casting 24 radiate outwardly to position the heater 10 in the casing. They do not have to be precise in length or location. Precise alignment of the bottom end of the equipment is less important than positioning concentrically in the casing of the deflector 44. As a general proposition, the spacing of the deflector plate should be relatively concentric with respect to the pipe 12. As will be understood, a chimney effect may occur which sweeps the heated gases upwardly against the casing.

While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic concept thereof, and the scope thereof is determined by the claims which follow.

Claims (19)

1. A method of manufacturing a chemical heater having a cast body including an upstanding neck extending from a bottom portion of said body, which comprises the steps of: (a) preparing a mold for casting said body; (b) blending the ingredients forming said body to form a castable mixture; (c) pouring said castable mixture into the mold completely filling the mold; (d) curing the castable mixture in the mold submerged in water to form a casting; (e) removing said casting from the mold; (f) air drying said casting; (g) curing said casting in an oven at a temperature of approximately 300 F; (h) removing said casting from the oven and allowing to cool; (i) packing a solid fuel compound in said casting; and (j) curing said casting and solid fuel mixture in an oven at a temperature of approximately 300 F driving off all volatiles.

2. The method of claim 1 wherein said ingredients forming said body comprise calcium aluminate, fine grained sand, expanded perlite, wire fibre, plastic, water and ice.

3. The method of claim 1 wherein said solid fuel compound comprises iron oxide, starch aluminum, perlite, hydroxol methyl celullose, and methanol.

4. The method of claim 1 further comprising the step of packing a quick-start mixture on top of said solid fuel compound for easily igniting said fuel compound.

5. The method of claim further including the step of positioning a tube about said neck defining a cavity therebetween and filling said cavity with a high heat refractory cement.

6. The method of claim 1 further including the step of reinforcing the base of said neck with wire positioned in the mold prior to pouring said cement mixture in the neck of the mold.

7. For use with a pipe to be welded, which pipe is in a surrounding concentric relationship and which requires preheating to an elevated temperature for a specified interval, a preheating apparatus comprising: (a) a supporting cylindrical casting sized to fit within a pipe to be preheated, said cylindrical casting including a bottom portion and defining a cavity; (b) a combustible solid fuel compound supported in said casting and having a generally cylindrical elongate outer surface conforming to the cavity defined by said cylindrical casting, said compound further being made of a material which burns at a controlled temperature for a specified interval to liberate heat in the form of upwardlyflowing gases;; (c) a deflector plate positioned above and spaced from said casting defining a gap therebetween, said deflector plate extending outwardly and arranged concentrically within the pipe to deflect the upward flow of heated gases radially toward the surrounding pipe; (d) integrally cast wire means adapted to support and position said cylindrical casting in the pipe; and (e) wherein said cylindrical casting is formed of a frangible material.

8. The apparatus of claim 7 wherein said deflector plate is formed of the same frangible material.

9. The apparatus of claim 7 wherein said bottom portion and said deflector plate are separated by a solid upstanding neck extending from said bottom portion toward said deflector plate and said neck is formed of a frangible material integral with said bottom portion.

10. The apparatus of claim 9 wherein said deflector plate, said neck and said bottom portion are all formed of a frangible material of cast cement and said solid fuel mixture leaves a frangible ash.

11. The apparatus of claim 7 wherein said cylindrical casting includes integral projections on the exterior thereof to centralize said cylindrical casting.

12. The apparatus of claim 7 wherein said solid fuel mixture includes binder material for binding non-toxic flammable materials comprising the fuel mixture material into a single structure conforming to the shape defined by the cavity of said cylindrical casting.

13. The method of welding a pipe by preheating a pipe section thereof, comprising the steps of: (a) positioning the solid fuel mixture within the pipe opposite the pipe section where a weld bead is to be formed; (b) igniting a combustible solid fuel mixture supported within the pipe; (c) heating the pipe section by convection to an elevated temperature by directing heated gases given off by the ignited fuel mixture against the pipe section; and (d) welding the pipe by forming a multi-pass bead.

14. The method of claim 13 wherein the heated gases are directed against the pipe section by a deflector plate positioned above the cylindrical casting.

15. The method of claim 14 wherein the solid fuel mixture is supported in a cylindrical casting sized to fit within the pipe.

16. The method of claim 13 wherein the solid fuel mixture comprises a cylindrical body suspended within the pipe.

17. A method of making a chemical heater, substantially as hereinbefore described with reference to the accompanying drawing.

18. Preheating apparatus, substantially as hereinbefore described with reference to the accompanying drawing.

19. A method of welding a pipe, substantially as hereinbefore described with reference to the accompanying drawing.