FIELD OF THE INVENTION
The present invention relates to a device for accurately measuring weld
reinforcement of butt welded joints of titanium tubes which eliminates the
problems of prior art. The invention further relates to a process for accurately
measuring weld reinforcement of butt welded joints of titanium tubes.
BACKGROUND OF THE INVENTION
Once through steam generators are made up of helically wound coils of Titanium
tube bundles. These tube bundles provide a heat transfer area in a constrained
space. The coils of these tube bundles are manufactured from Titanium tubes of
length 12-14 meters having one or more butt joints welded using an automatic
TIG welding machine.
PRIOR ART ACCEPTANCE CRETERIA FOR TUBE BUTT JOINTS IN A
PROCESS OF TITANIUM TUBE BUTT - WELDING ARE GENERALLY AS
UNDER:
1. Visual checks for ensuring freedom from weld defects and oxidized
colors.
2. Dimensional check for,
a. Weld width
b. Inside penetration
c. Weld reinforcement
3. Radiography
4. Hydro test
5. Helium leak test
All the acceptance criteria for the joints as stated hereinbefore are to be
implemented/completed before coiling.
According to the prior art, the process to measure weld dimensions are as
under:
a) Weld width: The required width of the weld can easily be checked using a
measuring tape and magnifying glass.
b) Weld defects & oxidized colors: Using magnifying glass of 10X, the visual
defects are checked and identified. The oxidized colors are checked with
respect to the acceptable/unacceptable colors of Ti welding charts by
comparison.
c) Weld inside penetration: By passing a Teflon ball having appropriate
diameter inside the Inner diameter of the tube after butt joint welding,
the inside penetration of the weld is determined.
d) Weld reinforcement Requirement: Weld reinforcement check is mandatory
and needs to be controlled within 0.2mm to 0.5 mm. If the actual value is
more than 0.50mm, then it may result in enlarged bundles or coils. Such
an un-desired over-dimension may disallow insertion of the bundle in a
given enclosing shell. On the other hand, if it is less than 0.2mm, it
serious affects the mechanical strength of the butt welded joint. Therefore
ensuring correct reinforcement at any orientation on the tube at its butt
joint is an important factor. According to the prior art, reinforcement
measurement check is performed using a dial gauge mounted on a device
disposed on the machine bed. At least eight equi-distant locations along
the circumference are identified and reinforcement of each butt joint is
checked.
According to the prior art, the measurement of weld reinforcements suffer
from poor repeatability including Non-repeatable readings due to the
clamping arrangements provided to hold the longer tubes (12-14M) on the
surface table/machine bed and rotation of the tube to measure at said eight
locations. Thus, the prior art fails to provide accurate data on weld
reinforcement dimension even after repeated measurements.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a device and method for
accurately measuring weld reinforcement of butt welded joints of titanium
tubes, which eliminates the disadvantages of prior art.
SUMMARY OF THE INVENTION
According to the invention, the acceptance parameters of weld reinforcement
of the butt joint titanium tubes are determined as under:
1. Provisions of a holding device on the welded tube near the joint for
reinforcement check, and thereby eliminate the clamping arrangement of
prior art.
2. Allowing 100% repeatability in measurement values.
3. Provisions of a portable gadget in particular an in-situ contrivance, to
decide about parameters change in welding.
4. Measurement of welding reinforcement on the welding location itself to
avoid movement of the welded tubes to different location and allow the
welder for changing weld parameter during welding procedure itself, in
case of reinforcement exceeding a threshold value.
According to the invention, an innovative dial gauge holding block having a
small arm with a hole and a locking means to attach a dial gauge, is
provided. At the bottom of the block a V groove is configured to position the
block on the tube so as to allow the measurement device to move forward to
measure weld reinforcement.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a generic detail about the dimensions of Titanium tube butt
joints.
Figure 2 - shows a prior art process for measurement of welding
reinforcement of titanium tube butt joints.
Figure 3 - shows a movable measuring device according to the present
invention.
Figure 4 - shows a welding machine with the inventive device in a mode of
implementing the measurement method of the invention.
DETAILED DESCRIPTION OF THE INVENTION
To perform the weld reinforcement check, as shown in figure 2, according to
the prior art, the tubes (item: 06) with butt joints are moved to an inspection
bay capable of accommodating a longer surface table (item: 01). Clamps
(item: 02) and fixtures (item: 03) required for holding the butt welded tubes
(item: 06) of length 12-14 meters are provided in the inspection area.
The tubes are kept on a V block (item: 05) and clamped. A dial gauge (item:
04) mounted on the fixture (item: 03) is allowed to move on the weld
reinforcement and the measurement data are recorded.
As opposed to prior art, the reinforcement check is conducted on the welding
machine (item: 09) itself according to the invention immediately after
completion of the welding. A V groove is provided at the bottom of a block
(07) holding the dial gauge (04). The holding block (07) slides on an outer
Diameter of the tubes (06). The dial gauge (item: 04) is mounted in the
holding block (07) and locked by a locking screw (item: 08) (see Figure
3). Accordingly, the welding reinforcement can be easily measured on eight
locations along the circumference of the butt-weld, and allow simultaneously
correction of welding parameters if needed at the welding time only.
OPERATIONAL STEPS OF THE DIAL GAUGE HOLDING BLOCK (Fiq.4)
1. Marking eight segments (at 45 degree interval) on outer diameter of the
tube (item: 06) after welding. The dial gauge holding block (07) is
enabled to work at any orientation;
2. Locating the V groove of the dial gauge holding block (item:07) on any
one of the segments;
3. Keeping the dial of the dial gauge (04) at zero value nearer to the
weldment, and slightly away from the weld;
4. Moving the dial gauge holding block (item: 07) towards the weld.
5. Keeping the plunger of the dial gauge (item:04) on the weld
reinforcement and record the dimension; and
6. Repeating the above steps for the remaining segments.
WE CLAIM:
1. A method for accurately measuring weld reinforcement of butt welded
joints of titanium tubes forming a heat transfer area in once through
steam generators the device comprising:
- providing an automatic TIG-welding machine enabled to carry out one or
more butt joints of titanium tubes to form tube bundles;
- providing a device in the form of dial gauge with a dial for measurement
of weld reinforcement values of the butt weld;
- providing a holding block with a V-groove to hold the measuring device;
- marking at least eight segments along the outer circumference of the
titanium tubes;
placing the measuring device on one of said at least eight segments on
the outer surface of the tube;
- moving the measuring device along the V-groove towards the weldment
and acquiring measurement data on weld reinforcement; and
- repeating the measurement step on other of the marked segments.
2. An improved device for accurately measuring weld reinforcement of butt
welded joints of titanium tubes forming a heat transfer area in once
through steam generators, the improvement is characterized by
comprising:
- a holding block for holding a measuring device and sliding on the butt
welded tube;
- a 'V' groove configured at the bottom of said holding block; and
- a locking means to lock the measuring device on the holding block.

ABSTRACT

The invention relates to a method for accurately measuring weld
reinforcement of butt welded joints of titanium tubes forming a heat transfer
area in once through steam generators the device providing an automatic
TIG-welding machine enabled to carry out one or more butt joints of
titanium tubes to form tube bundles; providing a device in the form of dial
gauge with a dial for measurement of weld reinforcement values of the butt
weld; providing a holding block with a V-groove to hold the measuring device
on said butt welded tube marking at least eight segments along the outer
circumference of the titanium tubes; placing the measuring device on one of
said at least eight segments on the outer surface of the tube; moving the
measuring device along the V-groove towards the weldment and acquiring
measurement data on weld reinforcement; repeating the measurement step
on other of the marked segments.