METHOD AND EQUIPMENT FOR HEAT TREATMENT OF LARGE TUBES

APPAREIL ET METHODE POUR LE TRAITEMENT THERMIQUE DE TUYAUX DE FORTES DIMENSIONS

English Abstract

A B S T R A C T
Method and apparatus for heat treating large thick-
walled tubes in which the tubes are heated in two stages
respectively involving flame and induction heating to
austenitic conversion temperature, the stock being
subsequently quenched.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of heat treating large tubes, comprising
heating the tubes in two separate stages to austenitic conversion
temperature, the first stage involving flame heating at high
energy density up to approximately Curie Temperature level and
the second stage involving inductive heating to austenitic
conversion temperature at low frequency for a duration which
corresponds at least to the time required for temperature
equalisation and temperature increase, the stock then being
quenched.
2. A method of heat treating large tubes according to
Claim 1, wherein the flame-heating process is applied by the
opposite draft or counterflow method with the tube set in
rotation.
3. Apparatus for performing the method according to
Claim 1 or Claim 2, wherein an air exhaust or outlet pipe is
provided concentric with the tube being treated and comprising
transporting means for the tube, an annular burner device
arranged forwardly of said air pipe which closely and concentri-
cally surrounds the tube to be heated and comprises burner
nozzles pointing in the direction towards the air pipe an inductive
heater device arranged in succession with the annular burner
and immediately succeeded by an exterior ring spray.

Description

This invention concer~.s a method of and apparatus or
installation for heat treating lar~e tubes 9 and more
specificall~ thick walled tubes.
It is common practice i~ the heat treatment or tempering
of tube~, and particularly o~ large tubes 9 to heat the stock
to austQnitic conversion temperature and ~uench by applying
a quenching medium to the inner and outer surfaces of the
tubes. Heat is applied either inductiYely or b~ ~eans of gas
burners. These conventional methods are rather complicated
and expensive and frequently it is not possible to control the
commencement of cooling. :
It is an object of this in~entîon to provide a method
of and apparatus or installation for heat treating or :;
tempering laree tubes which allow~ controlled treatment to be
applied particularly to thick-walLed tubes i~ a simple and .
economic manner.
According to the in~ention, a method ~f heat-treati.ng
tubes and particularly thick-walled tubes, comprises heating
the itubes in two separate stages to austenitic conversion
temperature, the first stage:involving flame heating at high
e~ergy density up to approximately Curie Temperature~level and
the second stage involving inductive heating to austenitic.
conversion temperature at low fre~uency for a duration which
corre~pond~ at least to the ~ime requlre~ for temperature
equali3ation and temperabure increase, the stoc~ then being
~ uenched.

From another aspect of the invention apparatus for
carrying out the aforesaid method comprises transporting
means for the tube, an annular burner device arranged
forwardly of said air pipe which closely and concentrically
surrou~ds the tube to be heated and comprises burner noz~les
pointing in the direction towards the air pipe an inductive
heatsr device arranged in succe~sion with the annular burner
~nd immediat~l~ succeeded by an exterior ring spra~.
. ~ .
The advantage~ of the method of this in~ention re~ide
in the combination of the economically favourable flame-
heating method with an even and uniform temperature equalisation
process, particularl~ for thick-walled stock, obtained
inductively at low frequency with the resulting pre~ention of
temperature differential~ across the thickness of the tube
walls during heat treatment.
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~ he accompanying drawing dlagrammatically illustrates
one embodiment of the apparatus of the in~entionO
In this apparatus the tuhes 1 are conYeyed in close
successlon with ths aid o~ conventional transporting devices
through an air pipe 2 and initially heated to approximately
Curie temperature by flame heating with the aid of an a~nular
burner 3 ~hereof the burner jsts po~nt in the dir~ction towasd~
the air pipe 2 to produce an opposi*e draft or countsrflow
flame heating process. The ~nnular burner 3 is succeeded ~ :
-
by an inductive heater d~ice 4 which in its tu~n s ~mmedlately
- followed by an ann~lar spray device or spr~y ring 5~ If
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required, a further ~pray ring may be additi onally provided
in the interior of the tube .
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