Description:DESCRIPTION
A METHOD FOR ASSESSING THE LOCAL POST WELD HEAT TREATMENT (PWHT) OF METALLIC PIPES
FIELD OF INVENTION
[0001] The present disclosure relates to local post weld heat treatment (PWHT) of butt joined metallic pipes. More particularly, the invention relates to a method for assessing the local post weld heat treatment (PWHT) of butt joined metallic pipes using nomograms.
BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] During welding, uneven heating and cooling of the weldment (the welded joint and adjacent areas) can lead to the buildup of residual stresses. These stresses can compromise the structural integrity and serviceability of the component.
[0004] While smaller, shop-fabricated weldments can be heat treated in an industrial furnace, larger components, particularly those fabricated in the field, cannot be treated this way due to their size and logistical constraints.
[0005] To address this, local PWHT methods are employed, often using resistance-based flexible ceramic pads. These pads are wrapped around the weldment to uniformly raise the temperature in the stress-relieving zone adjacent to the weld.
[0006] For effective heat treatment, it's crucial to maintain least temperature difference between the outer and inner surfaces of the pipe within a specific tolerance range. This uniformity is necessary to relieve stresses without introducing new stress.
[0007] The standard heat treatment parameters, often based on the geometry of the pipe, do not always guarantee successful local PWHT. Real-world observations have shown inconsistencies in achieving the temperature within the desired band.
[0008] The typical approach to ensure successful PWHT involves conducting extensive mock heat treatment trials. These trials are highly time-consuming (ranging from 8 to 48 hours) and consume a significant amount of energy (10,000 to 100,000 kWh). The process involves iterative adjustments of parameters until the desired outcomes are achieved and at sometimes are found unachievable using the present method.
PRIOR ARTS
A state of art US patent US5137025A discloses nomograms for interpreting electrocardiograms. The lines appearing on the nomograms contain a series of calibration curves relating to various cardiac rates, for a particular age group of persons. Using the nomogram, different interpretations can be drawn. The present invention although reveals a nomogram, is completely different from the above prior art. The present invention discloses a nomogram for assessing the feasibility of successfully conducting a local PWHT of pipe welds in field conditions and the method of generation of such a nomogram. These features are not seen in the above quoted prior art.
[0009] Another state of art US patent US20150344987A1 specifies method of performing a local PWHT in a weld seam present in a thin wall metallic body (shells containing satellite fuel) with special provision like cooling bands attached to the outside of the body on both sides of the weld seam and an inert atmosphere enclosure with inlet and exhaust ports fitted over the weld seam are maintained, with a view to heat treat the weld without thermally affecting the material adjacent to the weld. But, the present invention is totally different from the above prior art both in terms of scope and the method of application. The latter invention specifies a generation and usage of nomogram to assess the feasibility of successfully performing a local PWHT by meeting the required level of Through-thickness Temperature Gradient (TTG) and by using a power source of known power capacity.
[0010] Yet another state of art WO2013143282A1 explains a local heat treatment process of a thick-wall P92 pipeline in field condition, comprising the steps of calculation of heating width and insulating width, locally heating the pipe weld using a flexible ceramic resistance heater, to a temperature of 765°C on the outside diameter side, at the speed of 80°C/h after the temperature reaches 300°C, and preserving the heat for at least 4h at the rate of 5 min for the wall thickness of every 1 mm; decreasing the temperature of the pipeline to 300°C at the speed of 100°C/h and cooling the pipeline slowly to room temperature. The present invention is significantly different from the above mentioned prior art since the former does not reveal anything connected with the procedural steps to be followed for local PWHT, instead it has disclosed the method of generation and usage of a nomogram that would help in knowing the feasibility of carrying out a local PWHT within a required level of Through-thickness Temperature Gradient (TTG) and within the given rating of the heating power source.
[0011] A state of art US patent US7837810B2 describes about a special scheme of heat treatment meant for welds made in austenitic stainless steel materials wherein the thermo-mechanical properties of weld metal is substantially improved by the implementation of a post weld heat treatment that eliminates sigma phase in the heat treated zone and favours niobium carbo-nitride precipitate formation in a desirable size range. This is altogether different, in terms of scope and application of the present invention which mainly focuses on the development and method of use of a nomogram meant for assessing whether it is feasible to carry out a local PWHT of pipe welds within a desired level of Through-thickness Temperature Gradient (TTG) and within a given rating of the heating power source.
[0012] It is seen that the none of the prior arts cited above, have disclosed nomograms or procedure to develop nomograms for either assessing the TTG at the end of heat treatment or for arriving at the power source required to complete the heat treatment.
[0013] The prior arts in local PWHT face significant drawback such as time-consuming and labor-intensive, demand high energy consumption, lack flexibility for varying pipe sizes and geometries, often result in inconsistent outcomes, and typically require multiple iterative trials to achieve desired results. These limitations underscore the necessity for more efficient, adaptable, and reliable methods, particularly for large and complex weldments encountered in field conditions. Thus there is a pressing need to achieve the same.
OBJECTS OF THE INVENTION
[0014] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed herein below.
[0015] It is an object of the present subject matter to provide a method which overcomes the aforementioned and other drawbacks existing in the prior art fixture and methods.
[0016] It is a principal object of the present subject matter to introduce a method for assessing the feasibility of achieving Through-Thickness Gradient (TTG) for various pipe sizes and also to determine the power source rating needed for effective heat treatment.
[0017] It is another significant object of the present subject matter to propose the method to employ FE simulations to simulate local Post-Weld Heat Treatment (PWHT) on various pipe sizes, considering factors like resistance-based heat generation from flexible ceramic pads and heat transfer losses (conductive, convective, radiative).
[0018] It is another significant object of the present subject matter to propose the method to facilitate faster and more efficient evaluation of the feasibility of conducting local PWHT to meet success criteria (achieving TTG with available power source), bypassing the need for experimental trials.
[0019] These and other objects and advantages of the present subject matter will be apparent to a person skilled in the art after consideration of the following detailed description taking into consideration with accompanied drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION
[0020] This summary is provided to introduce the concept of a method for assessing the local post weld heat treatment (PWHT) of metallic pipes. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0021] The present invention discloses a method for assessing the local post weld heat treatment (PWHT) of metallic pipes. The method involves generating a first nomogram for assessing the Through-Thickness Temperature Gradient (TTG) in local Post Weld Heat Treatment (PWHT) of metallic pipes, generating a second nomogram for assessing the power source requirements in local PWHT of metallic pipes, selecting a pipe dimension and identifying its corresponding loci on the first and second nomograms, interpolating the TTG and power source requirements for the selected pipe dimension from the respective loci and assessing the feasibility of achieving the desired TTG and the adequacy of the available power source for conducting local PWHT based on the interpolated values.
[0022] In one aspect, the method for generating a first nomogram for assessing the Through-Thickness Temperature Gradient (TTG) in local Post Weld Heat Treatment (PWHT) of metallic pipes comprises of identifying a range of pipe sizes and corresponding geometrical and heat treatment parameters, conducting Finite Element (FE) simulations to model the transient thermal behavior during local PWHT, incorporating heat generation from resistance-based flexible ceramic pads and heat losses through conductive, convective, and radiative modes, recording and sorting the TTG results based on pipe dimensions and heat treatment parameters and developing the first nomogram by plotting the TTG results against pipe dimensions, with loci representing the variations in TTG for different pipe sizes and heat treatment parameters.
[0023] In another aspect, the method for generating a second nomogram for assessing the power source requirements in local PWHT of metallic pipes, comprises of utilizing the FE simulation data to determine the power input for various pipe sizes and heat treatment parameters and developing the second nomogram by plotting the power input results against pipe dimensions, with loci representing the variations in power source requirements for different pipe sizes and heat treatment parameters.
[0024] To further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit the scope of the present subject matter.
[0025] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
 
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0026] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of improved fixture or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which
[0027] Fig. 1 illustrates a schematic representation of nomogram to assess the TTG for various pipe dimensions for varying heat treatment parameters in accordance with an embodiment of the present disclosure;
[0028] Fig. 2 illustrates a schematic representation of nomogram to assess the rating of power source required for heat treating pipes of various dimensions for varying heat treatment parameters in accordance with an embodiment of the present disclosure;
[0029] Fig. 3 illustrates a graphical diagram of evaluation of TTG for a given pipe dimension for a given set of heat treatment parameters in accordance with an embodiment of the present disclosure; and
[0030] Fig. 4 illustrates a graphical diagram of evaluation of power source rating required for a given pipe dimension and for a given set of heat treatment parameters in accordance with an embodiment of the present disclosure.
[0031] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
[0032] A few aspects of the present disclosure are explained in detail below with reference to the various figures. Example implementations are described to illustrate the disclosed subject matter, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a number of equivalent variations of the various features provided in the description that follows.
[0033] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0034] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the “invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0035] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
[0036] Various embodiments are further described herein with reference to the accompanying figures. It should be noted that the description and figures relate to exemplary embodiments and should not be construed as a limitation to the subject matter of the present disclosure. It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the subject matter of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the subject matter of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof. Yet further, for the sake of brevity, operation or working principles pertaining to the technical material that is known in the technical field of the present disclosure have not been described in detail so as not to unnecessarily obscure the present disclosure.
[0037] The invention relates to a method to develop nomograms for the assessment of TTG for a given pipe size and to ensure the ability of a given power rating using FE experiments has been disclosed prior to the conduct of iterative, time consuming, energy intensive trials.
[0038] The method for assessing the local post weld heat treatment (PWHT) of metallic pipes comprises of the following steps:
• generating a first nomogram for assessing the Through-Thickness Temperature Gradient (TTG) in local Post Weld Heat Treatment (PWHT) of metallic pipes;
• generating a second nomogram for assessing the power source requirements in local PWHT of metallic pipes;
• selecting a pipe dimension and identifying its corresponding loci on the first and second nomograms;
• interpolating the TTG and power source requirements for the selected pipe dimension from the respective loci; and
• assessing the feasibility of achieving the desired TTG and the adequacy of the available power source for conducting local PWHT based on the interpolated values
[0039] Fig. 1 illustrates a schematic representation of nomogram to assess the TTG for various pipe dimensions for varying heat treatment parameters in accordance with an embodiment of the present disclosure. A method for generating a first nomogram for assessing the Through-Thickness Temperature Gradient (TTG) in local Post Weld Heat Treatment (PWHT) of metallic pipes comprises of
• identifying a range of pipe sizes and corresponding geometrical and heat treatment parameters;
• conducting Finite Element (FE) simulations to model the transient thermal behavior during local PWHT, incorporating heat generation from resistance-based flexible ceramic pads and heat losses through conductive, convective, and radiative modes;
• recording and sorting the TTG results based on pipe dimensions and heat treatment parameters; and
• developing the first nomogram by plotting the TTG results against pipe dimensions, with loci representing the variations in TTG for different pipe sizes and heat treatment parameters.
[0040] Further, the graphical representation where the X-axis denotes the pipe dimensions and the Y-axis denotes the TTG, with multiple loci indicating the TTG for various combinations of pipe sizes and heat treatment parameters.
[0041] Fig. 2 illustrates a schematic representation of nomogram to assess the rating of power source required for heat treating pipes of various dimensions for varying heat treatment parameters in accordance with an embodiment of the present disclosure; A method for generating a second nomogram for assessing the power source requirements in local PWHT of metallic pipes comprises of
• utilizing the FE simulation data to determine the power input for various pipe sizes and heat treatment parameters; and
• developing the second nomogram by plotting the power input results against pipe dimensions, with loci representing the variations in power source requirements for different pipe sizes and heat treatment parameters.
[0042] The graphical representation where the X-axis denotes the pipe dimensions and the Y-axis denotes the power source requirements, with multiple loci indicating the power source requirements for various combinations of pipe sizes and heat treatment parameters.
[0043] In the preferred embodiment, the range of pipe sizes for which nomograms and the range of variation of different parameters (one at a time) are identified. Transient FE simulation to simulate the local PWHT for the aforementioned samples, incorporating the effects resistance based heat generation from the flexible ceramic pads and the losses due to all three modes of heat transfer (conductive, convective and radiative) are performed. The TTG results and the power input pertaining to the variation of each of the geometrical and heat treatment parameters are recorded, sorted based on increasing diameter for the entire range and grouped based on wall thickness. Thus, a plurality of locus that are obtained as a result of connecting discrete TTGs are shown in nomogram Similarly, a plurality of locus connecting the power source requirement are shown in nomogram Each locus of TTG in nomogram 1 and power source requirement in nomogram 2 represent the maximum extent to which TTG can be reduced for a given pipe size and the maximum requirement of power source to conduct heat treatment, respectively. With the success criterions for a successful local PWHT, primarily evaluated based on achieving the TTG using the power source available at hand; the steps described below are followed to ensure a successful local PWHT.
[0044] In the TTG nomogram, where locus of TTGs obtained for variations in pipe dimensions are plotted against TTGs in Y-Axis and pipe dimensions in X-Axis (sorted with respect to increasing trend of diameter and grouped with respect to wall thickness); the pipe dimension for which prior assessment of achieving the desired TTG is noted and the corresponding TTG that could be achieved by adopting various combinations of heat treatment parameters are interpolated from the respective locus.
[0045] If the desired TTG cannot be achieved, then locus pertaining to alternative combinations of heat treatment parameters can be checked for the possibilities of reducing the TTG.
[0046] Upon identifying the heat treatment parameters that are capable of resulting in the desired TTG, the requirement of power source to conduct the local PWHT by meeting the aforementioned criterion is checked from the second nomogram, where locus of power source requirement obtained for variations in pipe dimensions are plotted against power source requirement in Y-Axis and pipe dimensions in X-Axis (sorted with respect to increasing trend of diameter and grouped with respect to wall thickness); the power source required is obtained by interpolating the pipe dimension with the locus corresponding to the heat treatment parameter (approach).
[0047] The advent of the FE method to generate nomograms avoids relying upon time consuming and energy intensive experimental trials that needs to be iterated for each material and each dimension. However, upon generation of nomograms, prior assessment of achievement of TTG for a given pipe size using the power source of said rating available at hand is made without the need of conducting experimental trials. This ensures faster evaluation of the feasibility of conducting local PWHT to meet the success criterions (achieving TTG using available power sources)
[0048] Further the nomograms are used for rapidly assessing the ability to successfully heat treat a given pipe dimension below the desired TTG after raising the temperature to the required heat treatment temperature and also to assess the ability of given power source to achieve the aforementioned criterion. The development, usage and the advantages are described in detail hereinafter.
[0049] The nomograms can be developed using experimental measurements; however, the use of transient FE simulation benefits the procedure by replacing the time consuming, energy intensive experimental method. Nonetheless, heat generation inside the flexible ceramic pads and the loss of heat through different heat transfer modes need to be necessarily incorporated with extensive care. Thus, with the simulation of local PWHT is done using FEM, the data on transient heat input and the TTG at the end of heating are recorded, sorted and grouped in a particular fashion to facilitate a field heat treated in meeting the aforementioned objective.
[0050] The range of pipe dimensions (diameter and wall thickness of pipes) that are commonly encountered and for which nomogram needs to be developed is finalized. The parameters that positively favors achieving the success criterions during the conduct of local PWHT like width of heating band, rate of heating, width of insulation band, variations in the aforementioned parameters by using values as a multiple of the parameter are noted. The extent of variation of each parameter that is assumed to aid the achievement of success criterions becomes the range. The TTG and heat input results pertaining to different pipe dimensions that are obtained as a result of varying heat treatment parameters are sorted based on increasing diameter of pipes, grouped based on wall thickness and plotted for various approaches. Each of the approach corresponds to a set of defined heat treatment parameters viz. Using standard deduced parameters, increasing the width of heat band alone with other parameters unaltered, reducing the rate of heating while other parameters are unaltered, etc.
[0051] The method to develop the first nomogram is by generating a loci connecting all the discrete TTGs pertaining to a selective approach (From FE results) within the group of wall thickness and pertaining to an approach (combination of heat treatment parameters). Each locus represents the maximum extent to which TTG can be reduced
[0052] The method to develop the second nomogram is by generating loci connecting all the discrete power source ratings pertaining to a selective approach (From FE results) within the group of wall thickness. Each locus represents the maximum power source required for heat treating pipes of various diameter but varying wall thickness.
[0053] For instance, the Figure 1 shows a plurality of loci pertaining to different approaches and different wall thickness. Each of which can be used for determining the TTGs of pipes with diameters ranging between the minimum and maximum diameters considered (Dia1 to Dia8). The continuous lines represent the extent of reduction of TTG that can be achieved for a set of pipes with same wall thickness but different diameters (when standard deduced heat treatment parameters are used). Similarly, the dashed lines and dotted lines represent TTGs for similar combinations of pipe dimensions (with variation in the heat treatment parameters).
[0054] In a similar fashion a plurality of loci pertaining to different approaches and different wall thickness showing the requirement of power source rating to successfully conduct the heat treatment by raising the temperature to the desired levels and by producing the desired TTG is shown in figure 2.
[0055] Fig. 3 illustrates a graphical diagram of evaluation of TTG for a given pipe dimension for a given set of heat treatment parameters in accordance with an embodiment of the present disclosure. The method of generation of a first nomogram that relates the outside diameters and wall thicknesses of pipes to the least possible Through Thickness Temperature Gradient (TTG) that can be achieved in performing the local Post Weld Heat Treatment (PWHT) of the said pipes, using resistance heating method. The first nomogram is drawn as a locus of multiple TTG values each of which are obtained by running a Finite Element simulation for a particular approach with a defined set of heat treatment parameters
[0056] The first nomogram comprises of a plurality of loci wherein each of the locus curves correspond to the TTG values achievable in performing local PWHT of various pipe sizes spread across the X axis of the said nomogram, using a specific approach with a defined set of heat treatment parameters
[0057] Fig. 4 illustrates a graphical diagram of evaluation of power source rating required for a given pipe dimension and for a given set of heat treatment. The method of generation of a second nomogram that relates the outside diameters and wall thicknesses of pipes to the maximum power required for performing the local PWHT of the said pipes, using resistance heating method. The second nomogram is drawn as a locus of multiple power rating values each of which are obtained by running a Finite Element simulation for a particular approach with a defined set of heat treatment parameter and comprising a plurality of loci wherein each of the locus curves correspond to the power rating values required for performing local PWHT of various pipe sizes spread across the X axis of the said nomogram, using a specific approach with a defined set of heat treatment parameters
[0058] The method facilitates the heat treatment operator with two nomograms; the first nomogram to assess the ability of standard specified parameters in successfully achieving the desired TTG in a pipe of given dimension and the second to assess whether the power source available at hand is capable of generating sufficient heat to rise the temperature of the pipe to the required heat treatment temperature. Further, the first nomogram suggests the best of the standard deduced parameters that respond well in reducing the TTG along with the level of variation required to reduce the TTG. The second nomogram complements the data obtained from first nomogram with the corresponding rating of power source for the variation of parameter. Thus, the method replaces the existing approach of conducting iterative experiments and ensuring the trustworthiness of standard specified parameters in achieving the desired TTG and the ability of power source to generate heat to suffice the heat treatment. The method conserves the time and resources that are presently utilised for conducting iterative experimental trials to ensure the ability of standard deduced parameters in successfully heat treating a given pipe by reducing the TTG to the desired levels.
ADVANTAGES OF THE INVENTION

[0059] The proposed method has the following advantages over the contemporary prior arts:
• Assessing the ability of standard deduced parameters in achieving desired TTG without conducting experimental trial.
• Assessing the effect of varying heat treatment parameters on the maximum possible reduction of TTG.
• Assessing the ability of power source available at hand in successfully completing the heat treatment by achieving the aforementioned success criterion, for standard deduced parameters and for predefined combination of variations in parameters.
• The nomograms replace the iterative, time consuming, energy intensive, experimental trials in assessing and ensuring the feasibility of fulfilling the success criterions during local PWHT of a given pipe size.
• Serves as a ready reckoner for the field heat treated in arriving at the heat parameters viz. width of heating band, rate of heating that will result in achieving the desired TTG.

TEST RESULT:
[0060] The test results pertaining to a SA387 Gr22 pipe of diameter 300mm and wall thickness 30 mm in terms TTG and power source requirement are as following:
[0061] The TTG can be achieved for a pipe of aforementioned dimension is deduced from the first nomogram as 19°C (less than the 20°C tolerance band). Similarly, the power source required for heat treating is deduced from the second nomogram to be 25KVA (less than 50KVA power source available at fabrication site).
[0062] Yet another example on the feasibility check for a pipe of same material and dimensions 300x50 results in a TTG of 22°C (exceeds 20°C tolerance band) and 26.5KVA (less than 50KVA power source available at fabrication site).
[0063] An example requiring higher capacity power source is portrayed using pipe of same material but of dimensions 1000x30. While, the TTG is less than 15°C, the power source required is 81KVA (Exceeds the capacity of power source available at site by a factor of 1.6)
[0064] The above description does not provide specific details of the manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[0065] Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other fixture or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0066] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0067] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different fixture or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
, Claims:We Claim
1. A method for assessing the local post weld heat treatment (PWHT) of metallic pipes, the method comprising:
generating a first nomogram for assessing the Through-Thickness Temperature Gradient (TTG) in local Post Weld Heat Treatment (PWHT) of metallic pipes, using FE simulation;
generating a second nomogram for assessing the power source requirements in local PWHT of metallic pipes, using FE simulation;
selecting a pipe dimension and identifying its corresponding loci on the first and second nomograms;
interpolating the Thickness Temperature Gradient (TTG) and power source requirements for the selected pipe dimension from the respective loci; and
assessing the feasibility of achieving the desired Thickness Temperature Gradient (TTG) and the adequacy of the available power source for conducting local Post Weld Heat Treatment (PWHT) based on the interpolated values.

2. The method as claimed in claim 1, wherein method for generating first nomogram for assessing the Through-Thickness Temperature Gradient (TTG) in local Post Weld Heat Treatment (PWHT) of metallic pipes, steps of:
identifying a range of pipe sizes and corresponding geometrical and heat treatment parameters;
conducting Finite Element (FE) simulations to model the transient thermal behavior during local PWHT, incorporating heat generation from resistance-based flexible ceramic pads and heat losses through conductive, convective, and radiative modes;
recording and sorting the TTG results based on pipe dimensions and heat treatment parameters; and
developing the first nomogram by plotting the TTG results against pipe dimensions, with loci representing the variations in TTG for different pipe sizes and heat treatment parameters.

3. The method as claimed in the claim 2, wherein the graphical representation where the X-axis denotes the pipe dimensions and the Y-axis denotes the TTG, with multiple loci indicating the TTG for various combinations of pipe sizes and heat treatment parameters.

4. The method as claimed in claim 1, wherein the method for generating the second nomogram for assessing the power source requirements in local PWHT of metallic pipes, comprising steps of:
utilizing the FE simulation data to determine the power input for various pipe sizes and heat treatment parameters; and
developing the second nomogram by plotting the power input results against pipe dimensions, with loci representing the variations in power source requirements for different pipe sizes and heat treatment parameters.

5. The method for generating the second nomogram as claimed in the claim 4, wherein the graphical representation where the X-axis denotes the pipe dimensions and the Y-axis denotes the power source requirements, with multiple loci indicating the power source requirements for various combinations of pipe sizes and heat treatment parameters.