FIELD OF INVENTION
This invention relates to determination of optimum preheat temperature for
welding of crack prone materials and enables welding without cracking. More
particularly, the invention relates a pre-crack test system to determine an
optimum preheat temperature enabling welding of materials without crack.
BACKGROUND OF THE INVENTION
Welding is one of the important tools for construction of various equipments and
structures for power plants, refineries, petro chemicals, ship building, steel rolling
mills etc. Different types of steels such as carbon steel, alloy steels and high
strength steels are used in the fabrication of equipments and structures.
Welding process is widely used in joining of steels for fabrication. During welding
of the steel materials, cracks are generally developed in the welded component
in case appropriate welding procedures are not adopted in welding of the steel.
The problem of cracking in welding processes can be substantially avoided if the
steel material is preheated to a sufficient degree prior to welding of the material.
The need for a preheating and the degree of preheat for welding the material
depends on many factors for example, type of steel, welding process parameters
and the welding consumable.
Repair of the crack in the welded component is more difficult than the original
welding. Sometimes the component which developed crack may not be
salvageable at all, and may have to be rejected. Huge expenditure is to be
incurred for rectification of the components with crack-defects.

OBJECTS OF INVENTION
It is therefore an object of the invention to propose a Pre-crack test system to
determine an optimum preheat temperature for producing crack-free weld-joints,
which eliminates the disadvantages of prior art.
Another object of the invention to propose a Pre-crack test system to determine
an optimum preheat temperature for producing crack-free weld-joints, which
enables optimizing the welding parameters influencing development of a weld-
crack.
A still another object of the invention to propose a Pre-crack test system to
determine an optimum preheat temperature for producing crack-free weld-joints,
which is enabled to evaluate and rank the welding consumables.
A further object of the invention to propose a Pre-crack test system to determine
and maintain an optimum preheat temperature for producing crack-free weld-
joints, which allows evaluation and ranking of steel materials to be used for
fabrication of equipment and structures.
SUMARRY OF INVENTION
The present invention enables joining of the steel materials with out cracking
problem during fabrication of structures or other equipments involving low alloy
steel, micro alloyed steel and quenched & tempered steel which are increasingly
used in the fabrication of pressure vessels, reactors, heat exchangers and
structures for various sectors of power, petrochemicals, ship building etc.

The Pre-crack test system of the invention comprises a load unit, a load sensor,
a temperature sensor, a hardened gripping means to hold the test samples, and
a sliding furnace. The load unit consists of a hydraulic power pack, a flow control
and pressure control valve. The sliding furnace comprises a rack and pinion
mechanism, an electric motor to slide the furnace back and forth, and electronic
controls to program the required temperature and maintain the temperature
within +/-5 degc accuracy.
The invented system is adapted to evaluate the weldability of steel for a process
of manufacture with compositional variation within the specified range. Similarly
the welding consumables of different make and or different formulations can be
checked with regard to hydrogen cracking susceptibility by adapting the system.
This system enable industries to determine the optimum preheat requirement for .
welding of the material. According to the system, a small cylindrical sample of 6
mm dia and 150 mm length from the material to be welded is taken and
assembled on the system. The test sample is preheated to a varying degree by
the sliding furnace which is a part of the equipment. The furnace can be moved
away from the test zone to facilitate assembling of the test samples and moved
back to the test zone for applying the preheat. A programmed control means in
the furnace enables maintaining a determined preheat. Welding is done on the
cylindrical sample and a load is applied after a predetermined time say, 1 minute.
The sample will fail / break if the applied preheat is inadequate. The preheat
temperature is varied until the sample does not break under the applied load.
This temperature where the sample does not develop a crack, is the optimum

temperature of preheat which can be applied on real welding construction to
avoid cracking problem.
The proposed Pre-crack test system has a unique configuration, a mechanism of
loading, a gripping means for the specimen, and a sliding type furnace.
The invention adapts a cooling means to avoid heat conduction to the load
sensor which ensures reliability of the pre-heat temperature determined.
The Pre-crack system of the invention is adaptable to optimise parameters of
welding with regard to cracking during fusion welding of steels, to evaluate and
rank the welding consumable, and equipment can be used to evaluate and rank
the material selected for manufacture of the equipment/structures.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a Pre-crack test system according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Figure 1 shows the proposed pre-crack test system. The test system comprises a
hydraulic power pack (1) which moves a piston (2) up and down. A hardened
gripping means (3) having a slot in which a first end of a test sample (4) is held.
A second end of the test sample (4) is guided thro a bush in a top plate (5) and
further into a hole drilled in a support plate. A furnace (6) is brought to this
location and heaters of the furnace are switched on. The temperature can be set

using a programmable control means (7). On reaching the pre-set temperature,
the furnace (6) is moved out of the test zone to facilitate a test welding of the
preheated sample (4). The test weld bead is laid on the head of a pin-support
plate. The ram is actuated down wards to apply a specific tensile load which is
measured by a load sensor (8) using a flow control (9) and a pressure control
valve (10). To avoid heat conduction from the furnace (7) through the test
sample (4) to the load sensor (8), a cooling means (11) is provided to the
gripping means (3). If the test specimen (4) breaks the pre-set temperature is
increased until the specimen (4) survives for a period of 16 hours. A temperature
corresponding to a pre-heat temperature of the sample (4), where the sample
(4) sustains a test-load of at least 16-hours, is considered the optimum
temperature of preheat which when applied in actual welding ensures crack free
welds in welding of steel materials.

WE CLAIM
1. A pre-crack test system to determine an optimum pre-heat temperature
for producing crack-free weld-joint, the system comprising:
- a hydraulic power pack structure (1) having a piston (2) enabled to move
upward and downward within the structure;
- a top plate (5) rigidly fixed on the upper portion of the structure (1);
- a gripping means (3) having a slot which locates a first end of a test
sample (4), a second end of the test sample (4) being guided through a
bush and a top plate (5) for locating on a support plate disposed above
the top plate (5) inside the structure;
- a removable furnace (6) having a plurality of heaters including a
programmable control (7), and disposed at a spaced-apart location, the
furnace (6) in an operative condition of the system is placed above the
hydraulic power pack (1) with the test-sample (4) disposed on the support
plate which allows a pre-heating of the sample at a pre-set temperature;
- a load sensor (8) for measuring the tensile load when applied through the
piston (2) on the test-sample (4), the load being controlled and
maintained by providing one each flow control and pressure control valve
(9,10);

- a cooling means (11) disposed on the gripping means (3) to maintain the
pre-heated temperature of the sample (4), the pre-heat temperature
being optimized at a value where the sample after preheat is enabled to
sustain a predetermined load for a pre-calculated time period without
breakage or developing a crack.
2. A pre-crack test system to determine an optimum pre-heat temperature
for producing crack-free weld-joint as substantially described and
illustrated herein with reference to the accompanying drawings.

A pre-crack test system to determine an optimum pre-heat temperature for
producing crack-free weld-joint, the system comprising a hydraulic power pack
structure (1) having a piston (2) enabled to move upward and downward within
the structure; a top plate (5) rigidly fixed on the upper portion of the structure
(1); a gripping means (3) having a slot which locates a first end of a test sample
(4), a second end of the test sample (4) being guided through a bush and a top
plate (5) for locating on a support plate disposed above the top plate (5) inside
the structure; a removable furnace (6) having a plurality of heaters including a
programmable control (7), and disposed at a spaced-apart location, the furnace
(6) in an operative condition of the system is placed above the hydraulic power
pack (1) with the test-sample (4) disposed on the support plate which allows a
pre-heating of the sample at a pre-set temperature; a load sensor (8) for
measuring the tensile load when applied through the piston (2) on the test-
sample (4), the load being controlled and maintained by providing one each flow
control and pressure control valve (9,10); a cooling means (11) disposed on the
gripping means (3) to maintain the pre-heated temperature of the sample (4),
the pre-heat temperature being optimized at a value where the sample after
preheat is enabled to sustain a predetermined load for a pre-calculated time
period without breakage or developing a crack.