FIELD OF THE PRESENT DISCLOSURE

The present disclosure relates to a coke drum for a delayed coker unit. Further, the embodiments of the present disclosure disclose the design and fabrication of the coke drum for a delayed coker unit.
BACKGROUND OF THE PRESENT DISCLOSURE
Generally, the coke drums are the heart of the Delayed Coker Unit which is one of the process units in many refineries. Delayed Coking is a thermal conversion process by which a residual stock or the crude's "bottom of the barrel" material is upgraded to more valuable distillates. This process also produces a solid carbonaceous matter called coke. The formation of coke takes place inside coke drum due to thermal cracking of the feed. Prior to introducing the hot liquid feed into the empty drum, the drum is gradually preheated from a temperature range of 135 °C to 150 °C to the target temperature range of around 330 °C to 375 °C by circulating hot vapour through the other drum. During the filling phase of the cycle, the preheated coke drum is filled with hot feed at about 500 °C. The hot feed is subsequently cracked thermally inside the coke drum. This process is known as "coking" process. The drum is subsequently cooled with steam and water during various steps at about 70 °C to 110 °C (quenching) and the coke formed inside is cut using high pressure water jet through a system known as hydraulic decoking system. The cooling, coke cutting, and removal process and further preheating is generally referred as "decoking" process. The unit normally takes the same amount of time for coking and decoking with the total cycle varying between 36 and 48 hours.

The repeated severe thermal stress cycles experienced by coke drums results in a phenomenon called ratcheting. Ratcheting causes cyclic straining of the material, which can result in failure by fatigue cracking and at the same time produce cyclic incremental growth of a drum, which frequently leads to the formation of permanent bulges or other forms of deformation on a drum. Experience indicates that the most pronounced bulging occurs in the lower to middle shell courses of a drum. This observed bulging has been attributed to large differences in the shell metal temperature from one area to another area in the drum. These local differences in the shell temperature, causes formation of local cold and hot spots, and are greatest during operating cycles when either hot (during initial filling) or cooler (during quenching) liquids enter the drum. This includes the initial filling of the drum with hot feed and when injecting water into the drum during the quenching operation near the end of the operating cycle. The coke drums thus experience fatigue and shell bulging due to the variation in operating pressure and operation temperature in cyclic operation of Coking and Decoking process.
Conventionally, the coke drums have been built by continuous circumferential weld seams and longitudinal weld seams being made offset between two adjacent shell courses, wherein the coke drum has a cylindrical shell in which all plates are placed horizontally in bottom section and top section as shown in Figures 1, 2 and 3. The horizontally placed plates form continuous circumferential weld seams and longitudinal weld seams in the cylindrical shell of the coke drum. The variable thickness in the shell courses and higher strength of weld metal in the circumferential girth welds cause differential yielding due to cyclic temperature and pressure loading and formation of local cold and hot spots. The resulting stiffening effects constrains the expansion of thicker shell and weld metal, while the thinner metal undergoes more straining due to ratcheting and ultimately fail due to cracking. Moreover, the allowable imperfections in fabrication of pressure vessels of welded construction present in the

circumferential weld seams grow to critical size during the cyclic operation and causes cracking and leaking of the fluids. The root cause of the shell bulging and cracking is due to the existence of strength undermatch between the shell courses and strength overmatch at girth seam welds and heterogeneous heating and quenching condition in axial / circumferential direction.
Accordingly, there is an immense need to develop a coke drum that overcomes the problems associated with the existing coke drums.
SUMMARY OF THE PRESENT DISCLOSURE
The present disclosure relates to a coke drum for a delayed coker unit. The coke drum comprising a cylindrical shell configured to support one or more components of the coke drum. The cylindrical shell comprising a top section, a continuous circumferential seam and a bottom section positioned below the top section, wherein the top section comprising a first plurality of plates placed horizontally in a zig-zag manner to form the top section. The continuous circumferential seam is placed between the top section and the bottom section, the continuous circumferential seam is adapted to join the top section and bottom section and the bottom section comprising a second plurality of plates placed vertically to form bottom section wherein the vertical plates reduce the probability of bulging and/or cracking in the cylindrical shell.
In an embodiment, the vertical arrangement of the second plurality of plates eliminate the circumferential weld seams in the bottom section which reduces the probability of bulging and/or cracking.
In an embodiment, each plate of the first plurality of plates is placed horizontally over another plate of the first plurality of plates to form the top section.

In an embodiment, one or more circumferential seams are positioned between two adjacent horizontally placed plates, one or more circumferential seams are shifted by half of the plate width to define a discontinuity in circumferential seam in the top section which minimizes the bulging and/or cracking in the top section.
In an embodiment, the continuous circumferential seam is adapted at the joining of the top and bottom sections to facilitate ease of fabrication and post weld heat treatment (PWHT) of the coke drum in two sections separately and final local post weld heat treatment (LPWHT) of the adapted seam.
In an embodiment, the first plurality of plates is placed horizontally to form top section and the second plurality of plates are placed vertically to form bottom section, wherein the combination of the first plurality of plates and the second plurality of plates, is configured to eliminate the circumferential weld seams in the bottom section of the coke drum which are inherently susceptible to cracking and at the same time facilitating ease of fabrication.
In an embodiment, the second plurality of plates are placed vertically to form bottom section having height around 12 to 15 meters or higher.
In an embodiment, the cylindrical shell comprising a top surface provided on a first end of the top section, the first end of the top section is positioned at a distance from the bottom section and a bottom surface provided on a first end of the bottom section, the first end of the bottom section is positioned at a distance from the top section.

In an embodiment, the coke drum comprising a dome shaped member placed on the top surface of the cylindrical shell and a conical member placed on the bottom surface of the cylindrical shell.
In an embodiment, the cylindrical shell has uniform diameter and uniform thickness throughout the length of the cylindrical shell including the top and bottom sections.
BRIEF DESCRIPTION OF FIGURES
Further aspects and advantages of the present invention will be readily understood from the following detailed description with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention wherein:
Figures 1, 2 and 3 illustrate a view of conventional coke drums comprising horizontally placed plates in the top and bottom section.
Figure 4 illustrates a perspective view of a coke drum in accordance with an embodiment of the present disclosure.
Figure 5 shows a typical plate arrangement of an 8.2 m diameter coke drum with optimum combination of horizontal and vertical plates in accordance with an embodiment of the present disclosure.
Figure 6 shows FE model: (a) Model 1 - Variable Thickness (b) Model 2 - Variable Thickness with 1:3 Taper(c) Model 3 - Uniform Thickness - Horizontal Plate (d)

Model 4 - Uniform Thickness - Vertical Plate in accordance with an embodiment of the present disclosure.
Figure 7 illustrates coke drum operating heating and cooling temperature cycle with a cold spot.
Figure 8 illustrates boundary conditions: (a) internal pressure (b) cold spot.
Figure 9 illustrates temperature (°C) distributions during formation of cold spot.
Figure 10 shows cyclic stress amplitude - strain amplitude curves @ 300 °C.
Figure 11 shows comparison of cyclic longitudinal stress-strain behaviour.
Figurel2 shows accumulation of plastic strain.
Figurel3 shows comparison of accumulated plastic strains.
Figurel4 shows equivalent von-Mises stress.
Figurel5 shows longitudinal (S22) and circumferential (S33) stress components (3rd cycle).
Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE
While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the invention.
Before describing in detail embodiments, it may be observed that the novelty and inventive step that are in accordance with the present disclosure resides in a coke drum. It is to be noted that a person skilled in the art can be motivated from the present disclosure and modify the various constructions of assembly, which may vary. However, such modification should be construed within the scope and spirit of the invention. Accordingly, the drawings are showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, equipment that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such setup or equipment. In other words, one or more elements in a system or apparatus proceeded by "comprises a" does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus. The following paragraphs explain present disclosure. The disclosure in respect of the same may be deduced accordingly.

Accordingly, the objective of the present disclosure is to provide a coke drum with the plate and weld seam arrangement for minimising proneness to shell bulging and/or cracking.
The present disclosure provides a coke drum for a delayed coker unit. The coke drum comprising a cylindrical shell configured to support one or more components of the coke drum. The cylindrical shell comprising a top section, a continuous circumferential seam and a bottom section positioned below the top section, wherein the top section comprising a first plurality of plates placed horizontally in a zig-zag manner to form the top section. The continuous circumferential seam is placed between the top section and the bottom section, the continuous circumferential seam is adapted to join the top section and bottom section and the bottom section comprising a second plurality of plates placed vertically to form bottom section wherein the vertical plates reduce the probability of bulging and/or cracking in the cylindrical shell.
The coke drums have always been a concern due to its various failure modes and maintenance issues across the world and it leaves scope for continuous development to enhance fatigue life and reduce maintenance. Among various issues, the majority of problems have been found related to bulging and/or cracking of shell and cracks in the skirt to bottom head joint.
The present disclosure has been carried out primarily on the coke drum shell plate arrangement to reduce the probability of bulge formation and/or cracking in the cylindrical shell. It has been found by various studies that coke drums experience bulging problem in the bottom section of the cylindrical drum, especially on shell courses above conical member. In a traditional coke drum construction, the plates are welded with continuous circumferential seams and longitudinal seams being made offset between two adjacent shell courses. It is also observed that the weld seams have

higher strength with respect to plate material and it acts like a stiffener ring. The root cause of the shell bulging is existence of strength overmatch at girth seam welds and heterogeneous heating / cooling condition in axial / circumferential direction. After few years of operation, bulges appear in the plate material and bulge keeps on growing as the number of cycles of operation increases (ratcheting phenomena). Accordingly, to reduce the occurrence of bulges, the present disclosures provide a coke drum which is provided with a different combination of vertical and horizontal weld seam arrangement. The bottom section of the cylindrical shell, which is more susceptible to bulging and/or cracking shall be made with plates arranged vertically, thereby eliminating the continuous circumferential seam, whereas the upper portion of the cylindrical shell is made of plates oriented horizontally and circumferential seams between two adjacent section is shifted by half of the plate width.
The coke drum of present disclosure also eliminates continuity of circumferential seam in the top section and thus reduces the probability of bulging and/or cracking. This discontinuity in circumferential seam will act as a bulge breaker. Also, in the event of any local bulging or weld cracking, window replacement can be carried out conveniently. The top and bottom sections of the cylindrical shell with bottom section made of vertical plate arrangement and top section made of horizontal plate zig-zag arrangement gives a tailor-made optimised arrangement to deal with bulging issues. This optimisation is carried out considering elimination of continuous circumferential seam except one at the joining of top and bottom sections of the cylindrical part of coke drum. This arrangement also facilitates ease of fabrication and post weld heat treatment of the drum. The top section, which is less susceptible to bulging has been provided with conventional horizontal plate for ease of fabrication and one continuous circumferential seam is allowed to facilitate PWHT of coke drum in two sections and final LPWHT at closing seam.

Accordingly, the present disclosure provides a system described with reference to the figures and specific embodiments; this description is not meant to be constructed in a limiting sense. Various alternative embodiments form part of the present invention.
Referring the figure 4, a coke drum (100) comprising a cylindrical shell (1) configured to support one or more components of the coke drum (100). The cylindrical shell (1) comprising a top section (2), a continuous circumferential seam (4) and a bottom section (3) positioned below the top section (2). The top section (2) comprising a first plurality of plates (5) placed horizontally in a zig-zag manner to form the top section (2). The continuous circumferential seam (4) is placed between the top section (2) and the bottom section (3), the continuous circumferential seam (4) is adapted to join the top section (2) and the bottom section (3). The bottom section (3) comprising a second plurality of plates (6) placed vertically to form bottom section (3) wherein the vertically placed second plurality of plates (6) reduce the probability of bulging and/or cracking in the cylindrical shell (1).
The cylindrical shell (1) defines a hollow portion to accommodate the material. The cylindrical shell (1) has uniform diameter and uniform thickness throughout the length of the cylindrical shell (1). The cylindrical shell (1) may be made of a suitable metallic material. The cylindrical shell (1) comprising a top surface (7) and a bottom surface (8). The top surface (7) is provided on a first end (top tangent) of the top section (2), the first end of the top section (2) is positioned at a distance from the bottom section (3). The first end of top section is a top tangent. The bottom surface (8) is provided on a first end of the bottom section (3), the first end of the bottom section (3) is positioned at a distance from the top section (2). The first end of bottom section is a bottom tangent.

The coke drum (100) comprising a dome shaped member (9) placed on the top surface of the cylindrical shell and a conical member (10) placed on the bottom surface of the cylindrical shell (1).
Each plate of the first plurality of plates (5) is placed horizontally over another plate of the first plurality of plates (5) to form the top section (2). Further, one or more circumferential seams are positioned between two adjacent horizontally placed plates (5), one or more circumferential seams are shifted by half of the plate width to define a discontinuity in circumferential seam in the top section (2) which minimizes the bulging and/or cracking in the top section (2).
The first plurality of plates (5) is placed horizontally to form top section (2) and the second plurality of plates (6) are placed vertically to form bottom section (3), wherein the combination of the first plurality of plates (5) and the second plurality of plates (6), is configured to eliminate the circumferential weld seams in the bottom section (3) of the coke drum which are inherently susceptible to cracking and increases the probability of bulging.
The second plurality of plates (6) is placed vertically to form bottom section (3) having height of 12 to 15 meters or higher. The vertical arrangement of the second plurality of plates (6) eliminates the circumferential weld seams in the bottom section (3) which reduces the probability of bulging and/or cracking.
The continuous circumferential seam (4) is adapted at the joining of the top and bottom sections (2, 3) to facilitate ease of fabrication and post weld heat treatment of the coke drum in two sections separately and final local post weld heat treatment of the adapted seam. This circumferential weld seam (4) shall not be a cause of bulging as there is no nearby second continuous circumferential weld seam.

The present disclosure provides a coke drum in which circumferential seams avoided at the bottom section of cylindrical portion which is very much susceptible to bulging and/or cracking. Further, the continuity of circumferential seam also avoided in top section of cylindrical portion. The fabrication activities are optimised by providing vertical plate at bottom section where it is more susceptible to bulging and horizontal plate at top section where it is less susceptible to bulging. In present disclosure, one continuous circumferential weld seam joining bottom section and top section shall facilitate PWHT of the two sections separately. This circumferential weld seam shall not be a cause of bulging as there is no nearby second continuous circumferential weld seam.
Referring to figures 6 to 15, which illustrates an example of the coke drum of the present disclosure wherein a case study of ratcheting simulation of the coke drum shell is conducted under thermo-mechanical loading with a cold spot using elastic-plastic finite element analysis (FEA) and the results are compared with the earlier conventional designs. The details of the geometry and FE model including loading and boundary conditions are given below.
1) Dimensions of the Coke Drum: Diameter (ID): 8550 mm
Vertical height: 35620 mm overall, 22750 mm tangent to tangent Shell Thickness: 38mm, 33 mm, 28 mm, 28 mm, 28 mm, 28 mm, 24 mm (from bottom to top shell courses)
Material: SA-387 Grade 11 Class 2 (1.25% chromium-0.5% molybdenum steel)
2) Type of Analysis and FE Model Details:

Analysis Type: Ratcheting simulation using elastic-plastic analysis (transient thermal and structural stress analysis)
Model Geometry: Bottom three courses of cylindrical shell with thicknesses of 38 mm, 33 mm and 28 mm, respectively. The length of the FE model is 9.0 m accommodating three horizontal shell courses of each 3 m in width and contains two circumferential weld seams. Quarter model (90 deg sector) is considered with appropriate boundary conditions.
FE Models (see Fig. 6): The following four FE models are considered for ratcheting
simulations.
Model 1, 2 and 3 are the conventional designs where shell courses are joined by
continuous circumferential weld seams, whereas Model 4 is the in accordance with an
embodiment of the present disclosure.
Model 1: Variable Thickness
Model 2: Variable Thickness with 1:3 taper
Model 3: Uniform Thickness - Horizontal Plate
Model 4: Uniform Thickness - Vertical Plate in accordance with an embodiment of the
present disclosure
Element Type: 3D Solid element
Material Model: Cyclic stress-strain curve (CSSC) @300 °C, Chaboche Nonlinear Kinematic Hardening (NLK) with four back stress components. The CSSC's for the base and weld metal are from Part 3 of ASME Sec. VIII Div.2. Ideally, the weld metal properties shall be identical to base material properties since fabrication requirement is maintaining weld properties in close match with the base metal.

Software: Abaqus/Standard, 2019
3) Applied Code
ASME Sec. VIII Div. 1 & 2, 2021 Edition & ASME Sec. II Part D, 2021 Edition
4) Loading and Boundary Conditions
Typical operating heating and cooling thermal cycle (see Fig. 7):
Duration of cycle: 48 hours
Heating rate: 1.3 °C/min
Cooling rate: 2.5 °C/min
Number of simulated cycles: 20 Cold spot (see Figs 7& 8):
Shape and Size: Ellipse with a semi-major axis of 1 m and semi-minor axis of
0.5 m.
Location: Center of mid-course of 3 shell course FE model
Duration (At): 30 min.
Temperature difference (AT) = 250 °C
Thermo couple temperature data obtained from the field and literature showed that the temperature difference ranges from 50 °C to around 300 °C can occurs randomly at the location of cold and hot spots. In the FE model, the cold spot is created by imposing a temperature difference of 250 °C lower than the temperature of its surrounding material during water quenching stage (see Fig. 7). In the simulation, it is assumed that the cold spot occurs at the same location repeatedly.

Boundary Conditions:
Appropriate symmetry boundary conditions are applied in the circumferential direction of the FE model. Bottom face of the model is fixed in the vertical direction and radial displacements are allowed.
The results of the above are explained below:
The objective of this case study is to carry out the ratcheting simulations using elastic-plastic analysis for the cold spot and to evaluate and compare the stresses / strains for four different coke drum shell course joining designs, i.e., Model 1 to 4 (see Fig. 6). The typical operating heating and cooling thermal cycle (see Fig. 7) and operating pressure cycle are imposed on the inner surface of the FE models. The assumed cold spot temperature profile is superimposed on the operating thermal cycle. Figure 8 shows the operating pressure and thermal boundary conditions applied to the FE Models. An adiabatic condition is applied on outer surfaces of the FE models. Sequentially coupled elastic-plastic transient thermo-mechanical stress analyses have been carried out and the effective stress and strain ranges and the accumulated plastic strains for the four designs are evaluated and compared. The ratcheting simulations have been carried out using general purpose commercial finite element software Abaqus, 2019.
Transient thermal analysis is performed for 20 cycles. The temperature distribution during the formation of cold spot is shown in Fig. 9 for Model 1 (typical). The obtained temperature distribution from transient thermal analysis is mapped on the structural model. The operating internal pressure cycle is also applied on the internal surfaces of the FE models along with the corresponding temperature distributions obtained from the thermal transient analysis at each time step. The longitudinal thrust pressure due to

internal pressure is applied at the top face of the FE models. The cyclic stress amplitude - strain amplitude curve for the base and weld metal are used as input, which is shown in Fig. 10.
Ratcheting simulations have been performed using a cycle-by-cycle cyclic plasticity algorithm with kinematic hardening model to simulate the loading, unloading and reloading phases of operating cycle, i.e., an assessment is performed by application, removal and reapplication of the pressure and temperature loadings. The results are extracted from the critical locations i.e., at the peripheral boundary of the cold spot. The cyclic longitudinal stress - strain behaviour is shown in Fig. 11. The accumulated equivalent plastic strain is shown in Fig. 12. From Figs. 11 and 12, it can be seen that ratcheting phenomenon is observed for Models 1 and 2, i.e., progression of the stress-strain hysteresis loop along the strain axis and shakedown is achieved for Models 3 and 4, i.e. only elastic primary and secondary stresses and no hysteresis loop. Figure 13 compare the accumulation of equivalent plastic strain at the end of 3rd, 10th and 20th cycles. The accumulated equivalent plastic strain is almost same for Model 3 and Model 4 and is much less as compared to Models 1 and 2. The percentage reduction of accumulated equivalent plastic strain for Models 3 and 4 as compared to Models 1 and 2 are as follows:
• 9%, 30%, 43% at the end of 3rd, 10th and 20th cycles, respectively - as compared to Model 1
• 5%>, 13%), 21%) at the end of 3rd, 10th and 20th cycles, respectively - as compared to Model 2
As described above, shakedown is achieved for Models 3 and 4 and also the accumulated equivalent plastic strain is reduced drastically as compared to Models 1 and 2. Therefore from the above results, it can be concluded that the proposed design

i.e., Model 4 can withstand the cold spot attacks and is bulge resistant and durable as compared to the conventional designs, i.e. Models 1 and 2.
The equivalent von-Mises stress is shown in Fig. 14. From Fig. 14, it can be seen that peak stresses are induced during the formation of cold spot. The longitudinal stress (S22) and circumferential stress (S33) components during the 3rd cycle is shown in Fig. 15. FromFig. 15, it can be observed that the longitudinal component of peak stress is tensile in nature and circumferential component of peak stress (S33) is compressive in nature and the magnitude of the longitudinal tensile stress is approximately 6 times the magnitude of the circumferential stress.
From the above description, it can be concluded that stress/strain response in the circumferential direction is much less as compared to the longitudinal direction. The induced high magnitude tensile stresses, during the formation of cold spot, further enhance its magnitude at the location of fabrication imperfections in the base / weld metal (e.g., flaws, linear indications, rounded indication, etc.) due to the effect of stress concentration (SFC). The magnitude of stress concentration at the location of imperfection is a function of imperfection type, size, geometry and its location in the thickness direction (inside/ outside surface or embedded) and nature of loading i.e., axial, bi-axial, etc. The range of theoretical SCF's is in the order of 3 to 6. Therefore, high magnitude cyclic tensile stresses in the longitudinal direction cause nucleation of new defects and/or growth of existing fabrication imperfections in the base/weld metal. This is in line with the industry observation that weld crack development is much active in the circumferential-radial plane for the coke drums.
Coke drums are designed in accordance with ASME Sec. VIII Div. 1 (Rules for Construction of Pressure Vessels). However, for fatigue evaluation and inspection, it is generally referred to ASME Sec. VIII Div. 2 (Rules for Construction of Pressure

Vessels, Alternative Rules) which is more stringent as compared to ASME Sec. VIII Div. 1. ASME Sec. VIII Div. 2 provides examination method and acceptance criteria and makes provision for an acceptable level of imperfections in fabrication of pressure vessels of welded construction. The practice is to accept pressure vessels, such as a coke drum, with certain known imperfections (e.g., flaws, linear indications, rounded indication, etc.) which are limited in size and distribution. For radiographic/ultrasound examination of welds, it provides certain acceptance criteria that specifies the maximum allowed size and distribution of imperfections in the fabrication welds. These imperfections act as stress/strain concentrators under cyclic loading and the severity of an imperfection is dependent upon its geometry.
It is concluded that the Models 1 and 2 exhibits ratcheting phenomenon and induces very high stresses / strains in the longitudinal direction. Therefore, Models 1 and 2 are susceptible to bulging and cracking in the circumferential direction, which is in-line with the industry experience. Even though Model 3 exhibits shakedown behaviour and the induced stresses / strains in the longitudinal direction are close to the Model 4 under ideal fabrication conditions (i.e., maintaining weld properties in close match with the base material), the actual stresses / strains may be very high due to the effect of stress concentration at the location of fabrication imperfections especially in the circumferential weld seams. The proposed optimum arrangement of vertical and horizontal plates, i.e., Model 4, eliminates the inherently susceptible circumferential weld seams from the active bottom section of the coke drum where formation cold and hot spots can occur due to severe local thermal transients and is more durable to bulging and fatigue cracking.

LIST OF REFERENCE NUMERALS :

Coke drum (100)
Cylindrical shell (1)
Top section (2)
Bottom section (3)
Continuous circumferential seam (4)
First plurality of plates (5)
Second plurality of plates (6)
Top surface (7)
Bottom surface (8)
Dome shaped member (9)
Conical member (10)
EQUIVALENTS
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and

modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

WE CLAIM:

1. A coke drum (100) for a delayed coker unit, the coke drum comprising:
a cylindrical shell (1) configured to support one or more components of the coke drum (100); the cylindrical shell (1) comprising: a top section (2) and
a bottom section (3) positioned below the top section (2), wherein; the top section (2) comprising a first plurality of plates (5) placed horizontally in a zig¬zag manner to form the top section (2);
a continuous circumferential seam (4) is placed between the top section (2) and the bottom section (3), the continuous circumferential seam (4) is adapted to connect the top section (2) and bottom section (3); and
the bottom section (3) comprising a second plurality of plates (6) placed vertically to form bottom section (3) wherein the vertically placed second plurality of plates (6) reduce the probability of bulging and/or cracking in the cylindrical shell (1).
2. The coke drum as claimed in claim 1, wherein the vertical arrangement of the second
plurality of plates (6), eliminates the circumferential weld seams in the bottom section
(3) which reduces the probability of bulging and/or cracking.
3. The coke drum as claimed in claim 1, wherein each plate of the first plurality of plates (5) is placed horizontally over another plate of the first plurality of plates (5) to form the top section (2).
4. The coke drum as claimed in claim 3, wherein one or more circumferential seams are positioned between two adjacent horizontally placed plates (5), one or more circumferential seams are shifted by half of the plate width to define a discontinuity in

circumferential seam in the top section (2) which minimizes the bulging and/or cracking in the top section (2).
5. The coke drum as claimed in claim 1, wherein the continuous circumferential seam (4) is adapted at the joining of the top and bottom sections (2, 3) to facilitate ease of fabrication and post weld heat treatment of the coke drum in two sections separately and final local post weld heat treatment of the adapted seam.
6. The coke drum as claimed in claim 1, wherein the first plurality of plates (5) is placed horizontally to form top section (2) and the second plurality of plates (6) are placed vertically to form bottom section (3), wherein the combination of the first plurality of plates (5) and the second plurality of plates (6), is configured to eliminate the circumferential weld seams in the bottom section (3) of the coke drum which are inherently susceptible to cracking, while maintaining ease of fabrication.
7. The coke drum as claimed in claim 1, wherein the second plurality of plates (6) is placed vertically to form bottom section (3) having height of 12 to 15 meters or higher.
8. The coke drum as claimed in claim 1, wherein the cylindrical shell (1) comprising: a top surface (7) provided on a first end of the top section (2), the first end of the top section (2) is positioned at a distance from the bottom section (3);
a bottom surface (8) provided on a first end of the bottom section (3), the first end of the bottom section (3) is positioned at a distance from the top section (2).
9. The coke drum as claimed in claim 7, wherein the coke drum (100) comprising:
a dome shaped member (9) placed on the top surface of the cylindrical shell; and
a conical member (10) placed on the bottom surface of the cylindrical shell.

10. The coke drum as claimed in claim 8, wherein the cylindrical shell (1) has uniform diameter and uniform thickness throughout the length of the cylindrical shell (1).