FIELD OF INVENTION
This invention relates to a process for preheating, welding and post weld heat
treatment of bundled 9Cr. 1 Mo tubes. More particularly, the invention relates to
a system for heat treatment of 9cr. IMo reheater tubes assembled in bundle.
BACKGROUND OF THIS INVENTION
The preheating is carried out to reduce the cooling rate in a welded component.
Further the required interpass temperature has to be maintained during welding.
After welding, there rests a requirement to reduce the magnitude of residual
stresses and HAZ hardness in a welded component, as otherwise, the welded
component would be vulnerable for failures during service. For the preheating
conventionally, the heating elements would be wound around the tube / pipe.
The problem arises when the steps of preheating, maintaining interpass
temperature during welding and the post weld heat treatment of tubes are to be
carried out in bundles, where the heating coils can not be wound around each
tube, as the pitch is very less.
A heat treatment device is disclosed in Japanese JP 2002343731 The device is
adhering to the inside surface of a joint and thereby preventing the treatables
from being contaminated.
A device and a method of heat treatment of a heating tube panel are disclosed in
Japanese 2002361470. The heat treatment device of the heating tube panel
comprises atleast one heating furnace for accommodating welded parts.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to propose a systenn for lieat
treatment of 9cr. 1Mo reheater tubes assembled in bundle, which eliminates the
disadvantages of the prior art.
Another object of the present invention is to propose a. system for heat
treatment of 9cr. IMo reheater tubes assembled in bundle which maintains the
interpass temperature during the steps of preheating, welding and post-weld
heat treatment of the tube bundle.
At the outset the description, which follows it is to be understood that the
ensuring description only illustrates particular form of this invention. However,
such a particular form is only an exemplary embodiment and the teachings of the
invention is not intended to be taken restrictively.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE
Fig. - 1 shows a schematic diagram of a system of heat treatment of 9cr. IMo
reheater tubes assembled in bundle according to the present invention.
SUMMARY OF THE INVENTION
Accordingly there is provided a system for heat treatment of 9cr IMo reheater
tubes assembled in a bundle, the tubes being bundled with close pitch such that
at least one tube each having higher outside diameter being disposed at two
extreme ends and the remaining tubes having identical outside diameter
intermediately interposed in the bundle, the system comprising a clamp for
holding the tube joints for each tube, at least one heating element for heat-
treatment of the tubes in the bundle, a power source, a controller connected to
the heating elements via a first end and to the power source via a second end. A
temperature recorder is operably connected to the controller. One heating
element each is wound around a top and a bottom of the reheater tubes
assembled in the bundle.
DETAIL DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The re-heater coils has atleast 12 tubes assembled in bundles. The outer most
tubes have higher OD than that of the other tubes. The tubes are assembled in a
close pitch. A clamp (3) has been provided to hold a tube joint (1) in position for
each tube. The resistance heating elements (2), so arranged that one coil each
around the top and bottom of the entire tube assembly, on either side of the
weld joint, would be wound. The heating elements (2) are insulated with glass
wool, to avoid heat losses during the heat treatment. The heating elements (2)
are connected to a controller (4) and a temperature recorder (5). The preheating
is carried out and after reaching the required pre-heat temperature, the welding
is started. After completion of the welding, the weld is allowed to cool down to
the required temperature. With the same set up, the post weld heat treatment is
carried out. After completion of the Post Weld Heat Treatment, necessary
mechanical tests can be conducted for qualifying the joint. The tube joint (1)
each represents the weld area of the top and bottom set of tubes arranges in
bundle. A power source is arranged (6) for supply of electrical power to the
heating elements via the controller (4), which controls the supply of electric
power to the heating elements.
WE CLAIM
1. A system for heat treatment of 9cr IMo reheater tubes assembled in a
bundle, the tubes being bundled with close pitch such that at least one
tube each having higher outside diameter being disposed at two extreme
ends and the remaining tubes having identical outside diameter
intermediately interposed in the bundle, the system comprising;
- a clamp for holding the tube joints for each tube;
- atleast one heating element (2) for heat-treatment of the tubes in
the bundle;
- a power source (6);
- a controller (4) connected to the heating elements (2) via a first
end and to the power source (6) via a second end;
- a temperature recorder (5) operably connected to the controller(4),
characterized in that atleast one heating element (2) each is wound
around a top and a bottom of the reheater tubes assembled in the
bundle.
2. The system as claimed in claim 1, wherein the heating element (2) is
insulated with glass wool.
3. A system for heat treatment of 9cr IMo reheater tubes assembled in a
bundle, as substantially described herein and illustrated with reference to
the accompanying drawings.

The invention discloses a system for heat treatment of 9cr 1Mo reheater tubes assembled in a bundle. The tubes are bundled with close pitch such that at least one tube each having higher outside diameter being disposed at two extreme ends and the remaining tubes having identical outside diameter Intermediately interposed in
the bundle. The system comprises a clamp(3) for holding the tube joints (1) for each tube, atleast one heating element (2) for heat treatment of the tubes (1) in the bundle, a power source (6), a controller (4) connected to the heating elements (2) via a first end and to the power source (6) via a second end. A temperature recorder (5) is operably connected to the controller (4). One heating element (2)
each is wound around a top and a bottom of the reheater tubes (1) assembled in the bundle.