Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-08-22
2003-04-22
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S624000, C073S640000, C073S641000
Reexamination Certificate
active
06550334
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic detecting apparatus, which is effective in inspecting defects on a surface joined by diffusion bonding.
2. Description of the Related Art
FIG. 28
shows an example of the structure of a furnace wall which is used in a plant or the like. This wall portion is a combination of a plurality of steel pipes
1
provided upright in parallel to one another with small distances therebetween and fins
2
provided between the individual steel pipes
1
.
When damage
3
occurs in one of the steel pipes
1
and mending, such as bonding is required, it is difficult for a worker to access that portion of the damage
3
which faces towards the inside of the furnace because of the small distances between the steel pipes
1
. To permit access to the damage not only from outside the furnace but also from inside, conventionally, welding was carried out after a scaffold
101
was set up inside the furnace as shown in
FIGS. 29 and 30
. Because putting up the scaffold
101
is time consuming, the mending takes a considerable time.
Conventionally, fusion welding in which a base metal
250
is cut into a V shape and padding is applied between the cut surfaces by welding has been common in bonding metal materials including iron and steel. A typical means for detecting a welding defect F at the padding is a P/S (Pulse Signal) probe type ultrasonic detecting apparatus which combines an ultrasonic transmitting element and an ultrasonic receiving element. As shown in
FIG. 32
, this ultrasonic detecting apparatus irradiates an ultrasonic wave perpendicular to the welded surface and receives the ultrasonic wave that returns through the same path, in order to detect a welding defect. The above fusion welding method requires several cutting processes and deforms the welded portion or thermally changes the composition. Securing a reliable welded portion with this method therefore requires highly skilled work and is costly.
Recently, there has been interest in the diffusion bonding method as one solution to the above problem. In this diffusion bonding method, an easily-diffusible thin metal sheet is positioned between the surfaces to be connected, and high temperature and pressure are applied to the portion near the surfaces to be connected in such a way that there is little plastic deformation, thereby diffusing atoms between the surfaces to be connected to accomplish bonding. Diffusion bonding has the advantages that it does not require any special skill and shows excellent performance, does not deform the outline of the connected surface and provides a connected surface with a uniform composition (see Japanese Unexamined Patent Application, First Publication No. 62-97784).
One metal-liquid phase diffusion bonding method which has been proposed is an amorphous bonding method which uses an amorphous sheet. This amorphous bonding method will now be discussed briefly with reference to the case where a steel pipe is bonded using an amorphous sheet containing boron which reduces the melting point. The amorphous sheet is a thin sheet made by rapid solidification and has a thickness of about 25 &mgr;m.
First, an amorphous sheet whose composition is similar to that of a steel pipe (base metal) and which contains boron is inserted between the surfaces to be connected. Then, the amorphous sheet is heated to a temperature equal to or lower than the melting point of the base metal and equal to or higher than the melting point of the amorphous sheet. Consequently, boron in the amorphous sheet is diffused in the parent phase, lowering the melting point of the parent phase and melting the parent phase. When heating is maintained in that condition, further diffusion of boron lowers the concentration of boron. This raises the melting point of the parent phase, so that the parent phase is gradually solidified, thus achieving bonding.
This bonding method has several advantages, such as a shorter bonding time, a simpler connecting apparatus structure and a lower heating temperature as compared with the conventional welding.
An apparatus which implements this amorphous bonding method will be described briefly with reference to FIG.
31
.
First, an amorphous sheet
72
is inserted between ends to be joined at the portion to be connected
34
of a steel pipe
1
. Next, the upper and lower steel pipes
1
are held by a clamp (not shown) and are urged in the directions of the arrows so as to push together the portion to be connected
34
. A high-frequency heating coil
104
heats the portion to be connected
34
which is under pressure from the clamp. The high-frequency heating coil
104
heats the portion to be connected
34
at a temperature equal to or higher than the melting point of the amorphous sheet
72
and equal to or lower than the melting point of the steel pipe
1
. The aforementioned amorphous bonding is carried out in this way.
However, the conventional apparatus does not operate on the premise of bonding of one of a plurality of steel pipes
1
that are arranged with the small distances therebetween, as mentioned previously. That is, steel pipes can be bonded by this apparatus when sufficient working space can be provided around the steel pipes
1
, whereas if a plurality of steel pipes
1
. are arranged with small distances therebetween, sufficient working space cannot be secured around each steel pipe
1
, and as a result, a high-frequency heating coil or the like cannot be set around the steel pipe
1
.
As the joined or connected surface is formed perpendicular to the material surface according to the diffusion bonding method, an ultrasonic wave cannot be irradiated perpendicular to the connected surface for detecting a welding defect F in the connected surface formed by the diffusion bonding method. This disables the use of a P/S probe type ultrasonic detecting apparatus which combines an ultrasonic transmitting element and ultrasonic receiving element. One method which uses the conventional P/S probe type ultrasonic detecting apparatus has been proposed in, for example, Japanese Unexamined Patent Application, First Publication No. 6-63771. According to this method, as shown in
FIG. 33
, surfaces to be connected are so cut as to have certain angles and are butted so that an ultrasonic wave can be irradiated perpendicular to the connected surface. However, this method is not practical because it is difficult to cut the base metal.
Ultrasonic inspection of a connected surface formed perpendicular to the surface of the base metal can be carried out by a double-probe method which has an ultrasonic transmitting element and ultrasonic receiving element separately installed in two probes as shown in FIG.
34
. This double-probe method uses an ultrasonic transmitting element and an ultrasonic receiving element separate from each other, reflects an ultrasonic wave inside the base metal to irradiate the ultrasonic wave on the connected surface at a predetermined angle, reflects the ultrasonic wave, reflected at the connected surface, in the base metal again and receives it at the receiving element.
However, the conventional double-probe method has a long propagation path for the ultrasonic wave in the base metal and uses multiple reflections which significantly attenuates the ultrasonic wave. What is more, because noise is occurs at every reflection, the sensitivity to detect minute defects is diminished. Those disadvantages make the conventional double-probe method impractical.
Accordingly, it is an object of the present invention to provide a connecting clamp, a connecting apparatus and a connecting method, which can allow a clamp section and heating member to be positioned around a rod member, such as a steel pipe, even if ample working space cannot be secured around the rod member. It is another object of this invention to provide an ultrasonic detecting method for inspecting a diffusion-bonded surface which has undergone simple material processing and which has a significantly improved defect detecting performance, an
Fujita Masaaki
Imamoto Toshihiko
Iwatsubo Kiyotaka
Kodama Masaru
Nishimura Nobuhiko
Larkin Daniel S.
Miller Rose M.
Mitsubishi Heavy Industries Ltd.
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