FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
PROVISIONAL / COMPLETE SPECIFICATION (See section 10 and rule 13)

1. TITLE OF THE INVENTION : A novel device and method for the heat treatment of weld joints involving asymmetrical mass distribution.
2. APPLICANT(S)(a) NAME : LARSEN & TOUBRO LIMITED(b) NATIONALITY: An Indian Company registered under the Provisions of The Companies Act, 1956.(c) ADDRESS : L & T House, Ballard Estate, MUMBAI-400001. Maharashtra State. India.
3. PREAMBLE TO THE DESCRIPTION
PROVISIONALThe following specification describes the invention. COMPLETEThe following specification particularly describes the invention and the manner in which it is to be performed.
4. DESCRIPTION (Description starts from page 2)5. CLAIMS: NA
6. DATE AND SIGNATURE: Given at the end of last page of specification.
7. ABSTRACT OF THE INVENTION: N.A.
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Title:
A novel device and method for the heat treatment of weld joints involving asymmetrical mass distribution.
Technical Field:
The present invention relates to a heat treatment process for weld joints involving asymmetrical mass distribution. More particularly, the present invention relates to a novel temperature-measurement arrangement and power-supply arrangement deployed in carrying out full proof heat treatment of a weld joint involving asymmetrical mass distribution.
Background and Prior Art:
For a weld joint to be effectively stress-relieved the weld joint and surrounding area must be heated to a suitable high temperature and held there for an extended period of time. On completion of the soaking period, the weld joint is uniformly cooled so that new stresses are not created. Measurement of temperature of the joint and adjacent area, and ensuring constant supply of heat energy during the heat treatment cycle are very critical tasks from the point of view of achieving the desired results, especially where structures with an asymmetrical distribution of mass around the weld joints are involved.
Hitherto, for measuring the temperature during heat treatment of such a welded joint with asymmetrical mass distribution around it, infrared temperature measurement technology is in use. Also a normal electrical power supply arrangement is used with or without a generator back-up, wherein there is no provision to assure continued on line power supply during the short time period of switching over from regular power supply to generator back-up, in the event of power failures on the regular supply lines, which are a commonplace phenomenon in the recent times.
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Drawbacks of Prior Art:
1. The temperature-measuring process used is costly and complicated.
2. In the event of a power failure, there is a danger of a thermal shock to the weld joint resulting into a costly and time-consuming rework. At times it may cause an irreparable damage to the weld joint that would then render the particular weld joint useless in operation, eventually marring the efficiency of the equipment wherein the said weld joint is used.
Summary of the Present Invention:
The object of the present invention is to have an improved heat treatment arrangement wherein the measurement of temperature is achieved using commonly available thermocouples in combination with a novel construction around the same.
It is a further object of the invention to have an improved heat treatment arrangement wherein a full proof constant power supply during the entire heat treatment cycle is assured.
Description of the Present Invention:
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the preferred embodiment.
In accordance with the present invention, a welded joint is given heat treatment to remove residual stresses. Stresses in the weld joints can result in cracking and early failure of the system.
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Device of the Present invention:
An Inconel casing is designed in two half-cylindrical parts, matching the weld joint geometry and is thermally insulated to avoid the heat losses.
The said casing is provided with six holes for insertion of heating sources and two separate holes for thermocouples. Two small holes are also provided in the casing for argon gas inlet and outlet. One thermocouple is positioned to rest on the weld joint and another at a specified distance away from the weld joint. Fixtures are used for fixing of thermocouples such that they are positively in contact with the metal below throughout the heating cycle.
The electrical power supply arrangement is equipped with a device to provide online uninterrupted power supply in the event of power failures, designed to automatically switch over into operation during the time period between such a power failure and the time the back-up generator is able to supply power as required.
The present invention thus provides a method of heat treatment of a weld joint especially a weld joint of a tube and a tube-sheet.
Method:
Spigots of the tubesheet and the thin tube is welded and checked for the integrity of the joints. The heat treatment on the weld joint is done as follows:
The two halves of inconel cartridge are placed around the weld joint. Sleeve-type Ni-Chrome heater with rating of 120 Watts are used as a heating source and are inserted in the cartridge. The temperature is measured through two thermocouples. K- type thermocouples are used for measurement of temperature. Argon purging is provided on ID and OD of the joint in order to eliminate the possibility of oxidation.
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Heat Treatment Cycle:
A typical heat treatment cycle of the welded joint may have the following
parameters:
• Loading temperature: 300 Deg C Max.
• Rate of heating: 200 Deg C/Hour Max
• Soaking temperature: 750 - 770 Deg C
• Soaking time: 30 Minutes Min.
• Rate of cooling: 200 Deg C/ Hour Max
• Unloading temperature: 300 Deg C Max
The heat treatment cycle is fully programmable with respect to loading and unloading temperature, rate of cooling and rate of heating and soaking time. The time temperature readings are recorded in the digital form and transformed to PC by software.
Advantages of the Present Invention:
1. That normal thermocouples are used to measure the temperature in place of a costly and complicated method of infrared sensing.
2. That the method used in present invention assures avoidance of a thermal shock to the weld joint in the event of power failures.
Salient Features of the Present invention:
1. The contact of thermocouples is maintained without welding the thermocouples to the weld joint/base metal, to ensure proper recording of temperature.
2. Un- interrupted power supply is maintained in order to avoid any thermal shocks that may otherwise leads to serious consequences like weld cracking.
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Dated this 31st day of January, 2007.

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