TECHN ICAL FIELD

The present disclosure is drawn to heating jackets for use on autoclave vessels that are robust with respect to cyclic heating.

BACKGROUND

Polymer use has dramatically increased over the past several decades due, at least in part, to the variety of material properties which are achievable and relatively low costs associated with formation of complex shapes. Both

continuous and batch polymerization processes are utilized for a variety of polymer production facilities. Each process has advantages and drawbacks depending on a variety of variables such as capital costs, throughput, polymer type, polymerization kinetics, and other priorities. Batch polymerization processes typically utilize a polymerization reactor or autoclave which is heated to an appropriate process temperature.

Heating of such polymerization reactors typically involves the use of closed loop heating systems which transfer heat from a heating fluid into the reactor. Heating systems can include exterior heating coils, internal heating loops, jacketed systems, or other similar heat transfer systems. Such systems can have inherent limitations in terms of heat distribution, heating rates, reliability, and operational constraints. As such, improvements to such heating systems on polymerization reactors continue to be sought and developed. SUMMARY

An autoclave heating jacket can include a heating fluid collar, a fluid inlet, a fluid outlet, and a plurality of fluid flow baffles. More specifically, the heating fluid collar can have an outer wall which includes an upper contact surface and a lower contact surface forming an enclosed chamber when engaged with an outer surface of an autoclave. The fluid inlet can be oriented through the outer wall and is capable of directing a heating fluid into the enclosed chamber. Similarly, the fluid outlet can be oriented through the outer wall and is capable of directing the heating fluid out of the enclosed chamber. The plurality of fluid flow baffles can be oriented within the enclosed chamber so as to direct the heating fluid along a predetermined pathway within the enclosed chamber.

A polymerization autoclave having a composite exterior heating assembly is also described. The polymerization autoclave can include an autoclave vessel body, a heating jacket, and a heating conduit. The autoclave vessel body can have an interior reaction chamber and an outer surface which includes an upper portion and a lower portion. The heating jacket can be attached to the lower portion forming an enclosed chamber. The enclosed chamber has a plurality of fluid flow baffles which are configured to direct heating fluid along a tortuous pathway within the enclosed chamber and about the lower portion. The heating conduit can be wrapped around and attached to the upper portion. More specifically, the heating conduit can have multiple wraps around the upper portion and is fluidly connected to the heating jacket. Accordingly, the heating fluid can be circulated through the enclosed chamber and the heating conduit to transfer heat into the interior reaction chamber. Further, the heating jacket and heating conduit collectively form the composite exterior heating assembly.

A method of repairing a polymerization autoclave with exterior heating coils attached to the outer surface is also disclosed and described. When the heating coils having weakened or leaking segments in a portion of the outer surface of the autoclave, such defects can be effectively repaired using the methods of the present invention. For example, the method can include removing the weakened or leaking segments of the heating coils from the affected portions of the outer surface of the autoclave to leave an intact heating coil segment on a separate portion of the outer surface. The heating jacket described above can be attached to the affected portions of the outer surface so as to form the enclosed chamber. The enclosed chamber can be fluidly connected to the intact heating coil segment. In this manner the polymerization autoclave can be repaired by providing a composite exterior heating assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a polymerization autoclave in accordance with one embodiment of the present disclosure;

FIG. 2 is a perspective view of an autoclave heating jacket with a partial phantom view showing obscured inside features in accordance with one embodiment of the present disclosure;

FIG. 3 is a cross-sectional cutaway view of a lower portion of a

polymerization autoclave in accordance with one embodiment of the present disclosure;

FIG. 4 is a bottom partial cutaway view of a polymerization autoclave in accordance with one embodiment of the present disclosure; and

FIG. 5 is a flow diagram of a method of repairing an external heating system for a polymerization autoclave in accordance with one embodiment of the present disclosure.

It should be noted that the figures are merely exemplary of several embodiments of the present invention and no limitations on the scope of the present invention are intended thereby.

DETAILED DESCRIPTION

Although the following detailed description contains many specifics for the purpose of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the herein disclosed embodiments.

Accordingly, the following embodiments are set forth without any loss of generality to, and without imposing limitations upon any claimed invention. Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as this may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

As used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a heating fluid" includes a plurality of such fluids and "an inlet" refers to one or more of such features.

In this disclosure, "comprises," "comprising," "containing" and "having" and the like can have the meaning ascribed to them in U.S. Patent law and can mean "includes," "including," and the like, and are generally interpreted to be open ended terms. The term "consisting of" is a closed term, and includes only the devices, methods, compositions, components, structures, steps, or the like specifically listed, and that which is in accordance with U.S. Patent law.

"Consisting essentially of or "consists essentially" or the like, when applied to devices, methods, compositions, components, structures, steps, or the like encompassed by the present disclosure, refers to elements like those disclosed herein, but which may contain additional structural groups, composition components, method steps, etc. Such additional devices, methods, compositions, components, structures, steps, or the like, etc., however, do not materially affect the basic and novel characteristic(s) of the devices, compositions, methods, etc., compared to those of the corresponding devices, compositions, methods, etc., disclosed herein. In further detail, "consisting essentially of or "consists essentially" or the like, when applied to devices, methods, compositions, components, structures, steps, or the like encompassed by the present disclosure have the meaning ascribed in U.S. Patent law and the term is open- ended, allowing for the presence of more than that which is recited so long as basic or novel characteristics of that which is recited is not changed by the presence of more than that which is recited, but excludes prior art embodiments. When using an open ended term, like "comprising" or "including," it is understood that direct support should be afforded also to "consisting essentially of language as well as "consisting of language as if stated explicitly.

Phrases such as "suitable to provide," "sufficient to cause," or "sufficient to yield," or the like, in the context of methods of synthesis, refers to reaction conditions related to time, temperature, solvent, reactant concentrations, and the like, that are within ordinary skill for an experimenter to vary to provide a useful quantity or yield of a reaction product. It is not necessary that the desired reaction product be the only reaction product or that the starting materials be entirely consumed, provided the desired reaction product can be isolated or otherwise further used.

It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range includes "about 'x' to about 'y'". To illustrate, a concentration range of "about 0.1 % to about 5%" should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1 %, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1 %, 2.2%, 3.3%, and 4.4%) within the indicated range. In an

embodiment, the term "about" can include traditional rounding according to significant figures of the numerical value. In addition, the phrase "about 'x' to 'y " includes "about 'x' to about 'y'".

The term "about" as used herein, when referring to a numerical value or range, allows for a degree of variability in the value or range, for example, within 10%, or, in one aspect within 5%, of a stated value or of a stated limit of a range.

In addition, where features or aspects of the disclosure are described in terms of a list or a Markush group, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. For example, if X is described as selected from the group consisting of bromine, chlorine, and iodine, claims for X being bromine and claims for X being bromine and chlorine are fully described as if listed individually. For example, where features or aspects of the disclosure are described in terms of such lists, those skilled in the art will recognize that the disclosure is also thereby described in terms of any combination of individual members or subgroups of members of list or Markush group. Thus, if X is described as selected from the group consisting of bromine, chlorine, and iodine, and Y is described as selected from the group consisting of methyl, ethyl, and propyl, claims for X being bromine and Y being methyl are fully described and supported.

As used herein, all percent compositions are given as weight-percentages, unless otherwise stated. When solutions of components are referred to, percentages refer to weight-percentages of the composition including solvent (e.g., water) unless otherwise indicated.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features that may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

Embodiments of the present disclosure employ, unless otherwise indicated, techniques of chemistry, metallurgy, welding, and the like, which are within the skill of the art. Such techniques are explained fully in the literature.

Batch polymerization reactions frequently involve repeated cycling of temperatures during various stages of processing. Typically, polymerization reactants are charged into an autoclave and the materials are heated sufficient to initiate polymerization and drive the reaction during the process. Once

completed, the materials are extruded or otherwise removed from the autoclave. Often intermediate cleaning and washing stages between polymerization batches can also be used to provide more consistent product quality. Unfortunately, such processes introduce significant cyclic variations in temperatures within the autoclave, along the autoclave walls, and along adjacent heating systems such as external heating coils. Furthermore, differentials in temperatures across each portion of the autoclave and heating system can create mechanical stresses at weld joints and adjacent materials.

As an illustrative example, formation of dyadic polyamides such as nylon 6,6 can involve reaction of a nylon salt with an acid at elevated temperatures around 189-250 °C for several hours. Autoclave wall temperatures are initially below typical heating fluid temperatures. Temperature and pressure conditions in a nylon 6,6 batch process cycle include variations during initial startup, charging of nylon salt, reaction stages, extrusion stage, and clean out stages. Among these various stages, temperatures changes create temperature differentials between the autoclave walls and heating coils.

Table 1 provides one example of cyclic polymerization operating conditions.

Table 1 : Temperature Conditions

Notably, the temperature differential between the heating coil and the autoclave wall can vary dramatically over time. External heating coils are most often welded to outer surfaces of the autoclave. During start-up of the reactor, expansion of the heating coil is restrained by the relatively cooler autoclave walls. This results in a compression load which exceeds elastic deformation limits of the welds. Such permanent deformation leads to stress in weld joints as autoclave walls subsequently heat up to normal operating temperatures. Similar

deformation results during variations in temperature conditions such as boil out, steam cleaning, washing, shutdown and startup of the reactor. In each case, changes in temperature results in a temperature gradient across the weld. In the case of nylon 6,6 production, batch cycle times can often range about 100-120 minutes for standard production volumes. Ultimately, such repeated temperature differentials lead to low cycle fatigue damage at weld joints between the external heating coils and the autoclave walls. Such damage is dominantly encountered in lower portions of the external heating coils because the heating fluid is the hottest near the lower inlet coils where the heating fluid temperature is the highest.

Consequently, temperature differentials between the heating coils and outer surface of the autoclave tend to be greater at lower portions of the external heating coils, and is especially pronounced within the first one to four wraps of the heating coil. Unfortunately, spot welding at failure locations can weaken cladded vessel walls over time and in some cases can cause delamination of the interior coating.

An autoclave heating jacket can be used overcome such damage and reduce future failure due to low cycle fatigue. FIG. 1 illustrates a polymerization autoclave 100 having a composite exterior heating assembly 102 which integrates such a heating jacket 104. The polymerization autoclave can include an autoclave vessel body 106, the heating jacket, and a heating conduit 108. The autoclave vessel body can be any suitable vessel in which a polymerization reaction can be performed. Generally suitable vessel bodies can include an interior reaction chamber which is enclosed by an autoclave wall and capable of pressurization. Although operating conditions can vary, the autoclave vessel body can be adapted to retain pressures of at least 300 psia, and in some cases at least 600 psia. The autoclave vessel body of FIG. 1 shows an upper primary inlet 1 10, a secondary inlet 1 12, and a pressure release valve 1 14. The inlets can be used to charge the interior reaction chamber with initial reactants, control pressure, and/or introduce staged polymerization reactants. It is noted that irrespective of the description and shown location of these inlets and valves, etc., these or other ports can be used differently than shown for any purpose designed by the user, as would be appreciated by one skilled in the art.

Optionally, the autoclave vessel can be a cladded vessel in which a primary vessel wall is coated with one or more interior layers. As a non-limiting example, a carbon steel wall can be coated with a stainless steel interior layer. The carbon steel wall can provide primary mechanical strength to the vessel while the stainless steel interior layer provides corrosion protection to inner surfaces of the vessel which are in contact with polymerization reactants and products at high temperatures and pressures. Other materials can also be suitable for vessel walls such as, but not limited to, carbon steel alloys (e.g. HII carbon steel), refractory metal alloys, chrome alloys, composites thereof, and combinations thereof. In one example, the vessel walls can be formed of a steel alloy of chromium-molybdenum (e.g. 16Mo3), or the like. Similarly, the interior coating layer can be stainless steel (e.g. SS321 ), or the like.

Vessel wall thicknesses can vary but are generally from about 15 mm to about 50 mm, and in many cases from about 20 mm to 40 mm. In one example, the vessel wall thickness can be 24 mm carbon steel with a 3 mm stainless steel interior cladding. Corresponding wall thicknesses of the heating conduit can also affect the degree of stress transferred to the heating coils during transitions in temperatures. Heating conduit wall thicknesses are typically less than vessel wall thickness and are generally less than about 25 mm. In one example, the heating conduit wall thickness can be from about 3 mm to about 6 mm and in a specific example 4 mm. Generally, the ratio of vessel wall thickness to conduit wall thickness can be from about 2: 1 to about 15:1 , or from about 5:1 to about 9:1 , for example.

Referring again to FIG. 1 , the autoclave vessel body 106 can have an outer surface 1 16 which includes an upper portion and a lower portion. The heating jacket 104 can be attached to the lower portion, while the heating conduit 108 can be wrapped around and attached to the upper portion. The terms "upper portion" and "lower portion" are relative terms, and do not imply the upper half and lower half, merely an upper portion with respect to the lower portion. The heating conduit can have multiple wraps around the upper portion. The number of wraps can vary considerably, but is often more than ten wraps, and in some cases up to or more than twenty. The heating conduit can also vary in outer width such as from about 50 mm to about 100 mm. Furthermore, each wrap typically has a small gap such that the outer surface is exposed in between successive wraps of the heating conduit. Such gaps are generally limited in order to improve heat transfer into the autoclave, but are most often limited to no more than 50% (and in many case less than 20%) of the width of surrounding heating conduit. The heating conduit can have a variety of cross-sectional shapes such as, but not limited to, half-pipe, full-pipe, U-channel, V-channel, and the like. The heating conduit can be fluidly connected to the heating jacket via a suitable coupling such as a transition chamber 1 18. Accordingly, heating fluid can be introduced into the exterior heating assembly 102 through a jacket fluid inlet 120 and circulated through the heating jacket to a jacket fluid outlet 122. A transition conduit 124 can direct the heating fluid to the transition chamber which fluidly connects to the heating conduit. In this manner, heat from the heating fluid can be transferred into the interior reaction chamber of the polymerization autoclave 100 in order to maintain desired temperatures. Although a variety of heating fluids can be used, non-limiting examples include Thermanol 66®, Dowtherm™, and mixtures thereof.

Optionally, the heating jacket can be attached to upper portions of the outer surface, while the heating conduit is attached to lower portions. In yet another alternative, multiple heating jackets can be attached to the outer surface in series. Multiple heating jackets can be directly connected to one another, or can be connected to intermediate heating conduit to provide alternating heating jacket-heating conduit configurations. The heating jacket and heating conduit can be attached to distinct and non-overlapping portions of the outer surface. Each of the heating jacket and the heating conduit can cover varying proportions of the outer surface depending on desired heat transfer performance and other considerations. However, as a general guideline, the heating jacket can cover from 3% to 40% of the outer surface, while the entire heating assembly can often cover from 30% to 80% of the outer surface, and often from 40% to 70%. In many embodiments, the heating jacket covers a lower portion of the outer surface and from about 5% to about 30% of surfaces covered by the heating assembly collectively. With respect to surface coverage, gaps between windings in heating conduit are included as covered by the respective heating device.

Turning to FIG. 2, the autoclave heating jacket 104 is shown in greater detail apart from the autoclave vessel body. The autoclave heating jacket can include a heating fluid collar 200, the fluid inlet 120, the fluid outlet 122, and a plurality of fluid flow baffles 202, 204, and 206. More specifically, the heating fluid collar can have an outer wall 208 which includes an upper contact surface 210 and a lower contact surface 212, forming an enclosed chamber 214 when engaged with an outer surface of an autoclave. The outer wall can have a circular shape which complements the outer surface of the autoclave providing a substantially annular volume for the enclosed chamber. Alternatively, the outer wall can have other shapes as long as the enclosed chamber is formed to allow heating fluid to pass long the outer surface of the autoclave.

The enclosed chamber includes the plurality of fluid flow baffles which are configured to direct heating fluid along a predetermined pathway within the enclosed chamber. A tortuous pathway can be designed within the enclosed chamber which flows about the lower portion of the polymerization autoclave. The tortuous pathway can be arranged so as to minimize non-uniformities in heat transfer into the interior reaction chamber. In FIG. 2, the fluid flow baffles include a dividing baffle 206 which forms a barrier within the enclosed chamber forcing heating fluid to flow circumferentially throughout the enclosed chamber. The fluid inlet 120 and fluid outlet 122 of the heating jacket can be oriented proximate one another such that heating fluid traverses substantially the entire enclosed chamber. The fluid inlet can be oriented through the outer wall 208 and is capable of directing a heating fluid into the enclosed chamber 214. Similarly, the fluid outlet can be oriented through the outer wall but is capable of directing the heating fluid out of the enclosed chamber.

As mentioned, a variety of baffles can be used to direct heating fluid flow along the tortuous pathway. The baffles can be oriented to define various tortuous pathways such as, but not limited to, serpentine fluid flow paths, circumferentially back-and-forth fluid flow paths, or the like. For example, alternating upper flow baffles 204 and lower flow baffles 202 can allow for a serpentine fluid flow path 216. Notably, each of the baffles includes an inner curved surface 218 which engages with the outer surface of the autoclave vessel body to force fluid flow around each baffle. Upper fluid flow baffles thus leave an open flow pathway above such baffles, while lower flow baffles leave an open flow pathway below corresponding baffles. Although the illustration shows a serpentine flow path which varied vertically, baffles can also be placed to induce horizontal flow variations. A variety of baffle arrangements can be used, although complex and or numerous baffle configurations can cause excessive pressure head. Such increased pressure within the heating assembly can increase chances of causing a failure within the heating assembly, need for high pressure heating fluid pumps, and/or increase operation costs. Regardless, the use of internal flow baffles provides for effective heat transfer volumes and substantial surface are coverage over jacketed lower portions of the outer surface. Such open enclosed chambers can provide non-uniform heating fluid flow pathways. In contrast, heating conduit typically has uniform cross-sectional areas (e.g. half- pipe, full pipe, or the like).

FIG. 3 illustrates the autoclave heating jacket 104 and heating coils 108 attached to the outer surface 1 16 of the polymerization autoclave. The heating jacket can optionally include a drain 300 in a bottom surface of the heating collar to allow for shutdown and/or cleaning of the heating assembly 102. As described previously, the heating jacket can include an upper contact surface 210 and a lower contact surface 212 which engage with the outer surface 1 16 of the autoclave to collectively form the enclosed chamber 214. In this embodiment, the upper contact surface can be a circular ridge defining a ceiling of the collar.

Similarly, the lower contact surface can be a circular flange defining a floor of the collar. Thus, the heating jacket can include the collar which has a circular vertical outer wall connected to the floor and the ceiling which collectively retain the heating fluid against the lower portion of the outer surface.

The heating jacket can be formed of any suitable material which is capable of withstanding expected operating temperatures, conditions and repeated temperature cycling. Non-limiting examples of suitable material includes carbon steel, stainless steel, steel alloys comprising chromium-molybdenum alloys (such as 16Mo3 and the like), and combinations thereof. In one example, the heating jacket can be formed of a chromium-molybdenum steel alloy. Typically the heating jacket can be welded to the outer surface using a high temperature weld alloy. Non-limiting examples of suitable weld alloys can include alloys comprising Mn-Mo, W2 Mo, G 46 AM G4MO, E Mo B32 H5, and combinations thereof.

Commercial weld alloys, (i.e. filler metals) such as, but not limited to, Nertalic 86®, Union® l-Mo, and SL® 12G, can likewise be used, to name a few.

Although other types of autoclaves can be used in connection with the heating assembly 102, internal heating manifolds can also be used. As an example, an internal heating manifold can include a conical reservoir 302 having an inlet 304. The conical reservoir can be housed within a lower section 306 of the autoclave which is attached to the vessel body 106 at flange 308. The lower section includes an autoclave outlet 310 which allows for removal of product from the interior reaction chamber 312 for further processing (e.g. extrusion, drawing into fiber, molding, etc.). In some cases, the lower section can have a wall thickness which is larger than a wall thickness of the primary vessel wall 313. For example, the lower section thickness can be about 10% to 40% greater than the primary vessel wall thickness. Similarly, a jacket thickness can be 10% to 40% greater than corresponding heating conduit. Although other thicknesses can be used the jacket can have a thickness from about 8 mm to about 25 mm, and in some cases 10 mm to 18 mm. As an example, the heating jacket can have 12 mm or 16 mm thickness. In another example, the outer shell wall can have a lower thickness than the ceiling and floor thicknesses. As with the heating conduit, a ratio of the lower section thickness to the heating jacket thickness can be from about 2: 1 to about 15:1 , and in some cases from about 5:1 to about 9:1 .

The internal heating manifold can further include one or more heating tubes 314 which are each fluidly connected to the conical reservoir. The heating tubes can be connected (not shown) to a common outlet 316 for recycling and/or reheating of cooled heating fluid. In yet another alternative, the polymerization autoclave can be an agitated autoclave which includes an internal mixer. The internal mixer can typically be oriented vertically along a centerline of the interior reaction chamber. Internal mixers can allow for increased uniformity of polymerization conditions and decreases in polymerization reaction times.

Referring now to FIG. 4, a bottom view of the polymerization autoclave 100 shows the autoclave heating jacket 104 attached to the autoclave vessel body 106. As described above, the vessel body is attached via flange 308 to the conical lower section 306 having the autoclave outlet 310. In some cases, the heating coils 108 are formed as half pipes welded directly to the outer surface of the vessel body. As mentioned previously, the vessel body can be a cladded vessel which includes a primary wall 402 and an interior coating 404.

As part of the heating assembly, the transition conduit 124 can fluidly connect the fluid outlet 122 into the transition chamber 1 18. The transition chamber then directs heating fluid flow into the half-pipe heating coil 108 as shown by fluid flow path 406. As such, the heating assembly can be a composite heating system which effectively utilizes the heating jacket over lower portions of the polymerization autoclave in conjunction with more traditional half-pipe heating coils to achieve improved performance.

The aforementioned heating jackets can be advantageously used in original construction of polymerization autoclaves. However, such heating jackets can find particular use in repairing and/or improving reliability of existing autoclaves. Accordingly, FIG. 5 shows a method of repairing a polymerization autoclave with exterior heating coils attached to the outer surface 500. In such cases, standard heating coils (e.g. half-pipe conduit) can extend from a bottom portion of the autoclave outer surface up to an upper portion of the outer surface. Typically, such heating coils are wrapped at least half-way up the outer surface. Regardless, portions of the heating coils can begin to fail due to low cycle fatigue. This is most commonly associated with initial portions of the coils where the heating fluid is at a maximum (e.g. when temperature differentials are also at a maximum during temperature transitions). When the heating coils have weakened or leaking segments in a lower portion of the outer surface of the autoclave, such defects can be effectively repaired using the methods of the present invention. The method can include removing the leaking segments of the heating coils 510 from the lower portions of the outer surface of the autoclave. A functioning portion of the heating coil is left as an intact heating coil segment on an upper portion of the outer surface. The leaking segments can be removed using any suitable technique which does not adversely affect the vessel body or neighbouring welds or joints. In one alternative, the leaking segments can be removed by grinding. Other mechanical techniques can also be used such as, but not limited to, plasma cutting, torch cutting, metal cutting saws, laser cutting, and the like. The exposed outer surface can then typically be cleaned. Cleaning can include one or more steps of polishing, washing, surface treatment, and surface coatings.

Once the exposed outer surface is prepared, the heating jacket described above can be attached 520 to the lower portions of the outer surface so as to form the enclosed chamber. The heating jacket can be most often attached by welding. Non-limiting examples of welding techniques include gas tungsten arc welding (GTAW), shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and the like. Overlapping offset weld deposits in building up weld joints can be used to increase weld joint strength. Furthermore, weld joints can be full penetration welds (i.e. as opposed to tack welds or partial penetration welds).

Referring again to FIG. 5, the enclosed chamber can be fluidly connected

530 to the intact heating coil segment. This can involve attaching a transition conduit and/or transition chamber to connect the heating jacket to the heating coils. As with securing the heating jacket, the transition chamber or other connections can be secured using welding techniques. Such welding techniques can provide long term service of the heating assembly under a variety of operating conditions. Regardless, the connection can be secured to prevent leaking of heating fluid from the external heating assembly and to withstand typical operating conditions. In this manner, the polymerization autoclave can be repaired or improved by providing a composite exterior heating assembly.

The heating jackets and heating assemblies described herein can provide effective heat transfer, while also minimizing or eliminating chances of low cycle fatigue. As a result, polymerization autoclaves incorporating such external heating devices can provide increased service life, higher reliability, and more uniform heat distribution.

Although the subject matter has been described in language specific to structural features and/or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements can be devised without departing from the spirit and scope of the described technology.