jaeri-tech 96-035

JAERI-Tech96-035

JAERI-Tech-96-035JP9609136

JP9609136

DEVELOPMENT OF REMOTE BORE TOOLSFOR PIPE WELDING/CUTTING BY YAG LASER

Kiyoshi OKA, Masataka NAKAHIRA, Satoshi KAKUDATE, Eisuke TADA,Kenjiro OBARA, Kou TAGUCHI and Naokazu KANAMORI

Japan Atomic Energy Research Institute

m 0 1

( T 3 1 9 - 1 1

is

This report is issued irregularly.

Inquiries about availability of the reports should be addressed to Research Information

Division, Department of Intellectual Resources, Japan Atomic Energy Research Institute,

Tokai-mura, Naka-gun, Ibaraki-ken 319-11, Japan.

© Japan Atomic Energy Research Institute, 1996

JAERI-Tech 96-035

Development of Remote Bore Tools for Pipe Welding/Cutting

by YAG Laser

Kiyoshi OKA, Masataka NAKAHIRA, Satoshi KAKUDATE, Eisuke TADA

Kenjiro OBARA, Kou TAGUCHI and Naokazu KANAMORI

Department of Fusion Engineering Research

Naka Fusion Research Establishment

Japan Atomic Energy Research Institute

Naka-machi, Naka-gun, Ibaraki-ken

(Received July 4, 1996)

In D-T burning reactors such as International Thermonuclear Experimental

Reactor (ITER), an internal access welding/cutting of blanket cooling pipe

with bend sections is inevitably required because of spatial constraint due to

nuclear shield and available port opening space. For this purpose, an internal

access pipe welding/cutting using YAG laser beam is being developed according

to the agreement of the ITER R&D task (T44). A design concept of welding/cutting

processing head with a flexible optical fiber has been developed and the basic

feasibility studies on welding, cutting and rewelding are performed using

stainless steel plate (SS316L). In this report, the details of a welding/cutting

head with a flexible optical fiber for YAG laser are described, together with

the basic experiment results relating to the welding/cutting and rewelding.

Keywords I Fusion Experimental Reactor, Internal Access Pipe,

Welding/cutting Equipment, YAG Laser, Blanket Cooling Pipe Maintenance,

Branch Pipe, Bend Pipe

This work is conducted as a ITER Technology R & D and this report corresponds to 1994 ITER R&D

Task Agreement (T44).

JAERI-Tech 96-035

B

it-

(1996^7 fl 4

: T311-01

JAERI-Tech 96-035

Contents

1 . Introduction 1

1.1 Task Objective - 1

1.2 Scope of the Report 1

2. Design Concept for the Blanket Maintenance 2

3. A Processing Head of YAG Laser System 3

3.1 Constitution of Processing Head 3

3.2 Performance Tests of Processing Head 5

4. Welding/cutting Characteristics 7

4.1 Basic Welding Test 7

4.2 Cutting Test 10

4.3 Rewelding Test 18

5. Conclusion 20

Acknowledgment 21

References 21

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JAERI-Tech 96-035

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IV

JAERI-Tech 96-035

1. INTRODUCTION

1-1. Task Objective

The objective of this task is to develop the remote bore tools for welding and cutting of

the blanket cooling pipe from the inside. The bore tools are inevitably required for the blanket

cooling pipe maintenance since an external space around the pipe to be welded and cut is too

narrow to access. According to the current machine layout, the bore tools should be designed

to move at least 10 m along the cooling pipe so as to reach the position where the pipe is

welded and cut. In addition, the operation of welding and cutting has to be performed under

high gamma radiation dose rate of 3x106 R/h.

1-2. Scope of the Report

The development of the remote maintenance technology is essential to realize ITER H],

because the reactor components are activated by 14-MeV neutrons. Particularly, the in-vessel

components, such as divertor plates, armors and blanket/first wall modules, are the most

critical ones in terms of maintenance of the reactor. The blanket/first wall module is categorized

into the scheduled maintenance which includes complete change out from shielding to breeding.

Therefore, reliable and quick maintenance operations are highly required for the blanket/first

wall module. Figure 1.1 shows a schematic view of the blanket/first wall module

maintenance system proposed for ITER. After the cooling pipes of the blanket/first wall

module are cut, blanket/first wall modules are removed through the horizontal port using an in-

vessel manipulator and transporter. A number of cooling pipes are connected to the modules

through a relatively narrow space located behind the modules, so that the external space around

the pipes is not sufficient to allow an access of an ordinary TIG welder or mechanical cutter.

A new maintenance technology based on a CO2 laser beamC2-3'4^ and a YAG laser

beamt5] has been developed for welding and cutting of cooling pipes by the internal access.

The YAG laser system based on laser beam transmission using a flexible optical fiber inside the

pipe has been selected since the pipe welding/cutting by the internal access can be available

even for the pipes with bend and branch.

The remote bore tools based on YAG laser are essential technology with regard to the

realization of the current modular type blanket concept. The main issues relating to this

technology are mobility of the tool to move inside the pipe through several bend sections for

accessing to the branch pipe, controllability for positioning, welding and cutting, and

qualification of welding and cutting including edge preparation and misalignment.

A prototypical processing head has been fabricated and tested to demonstrate the

fundamental mobility for traveling inside a 100 mm pipe with a bend radius of 400 mm and for

accessing from the 100 mm pipe to a branch pipe with a diameter of 50 mm. In addition, the

welding and cutting conditions performance is also verified using this processing head. In

parallel, welding and cutting experiments using the ordinary YAG laser system have been1

JAERI-Tech 96-035

conducted in order to specify the welding and cutting conditions including effects of gaps and

surface treatment on weldability.

This report covers the following results obtained from the prototypical processing head

fabrication and the basic welding and cutting experiments.

(1) Bore tool for welding/cutting using YAG laser

Design, fabrication and functioning tests of a prototypical processing head

developed for welding/cutting of branch pipe from cooling manifold

(2) YAG laser welding and cutting

1) Welding experiments including effects of gaps, laser power and process

speed on weldability

2) Cutting experiments as a function of process speed, laser power and assist

gas

3) Rewelding experiments using samples cut by YAG laser

4) Mechanical tests of welded samples with different conditions

2. DESIGN CONCEPT FOR THE BLANKET MAINTENANCE

According to the ITER EDA design, the blanket is composed of blanket/first wall

modules poloidally segmented, strong back plates and cooling manifolds located between the

modules and the back plates. The cooling manifolds are attached to the back plate and each

module is connected to the back plate individually. In this configuration, a branch pipe has to

be connected between the manifold and the module for cooling. The proposed YAG laser

system is based on laser beam transmission using a flexible optical fiber installed inside the

pipe. Hence, the pipe welding/cutting by the internal access can be available even for the pipes

with bend section and branch. Figure 2.1 shows a schematic view of the YAG laser

processing head approaching to the branch pipe welding/cutting from the inside of the cooling

manifold: this processing head can be moved through the cooling manifold with a minimum

bending radius of 400 mm. The processing head has the following features;

(1) Traveling mechanism through the cooling manifold with curved sections

(2) Telescopic mechanism to approach from the manifold to branch pipe for

welding/cutting

(3) Position adjustment and fixing mechanism for welding/cutting

In this study, specifications of the blanket cooling pipe are considered as listed in Table

2.1, which are prepared by JCT as the design guideline. Figure 2.2 shows the basic pipe

layout proposed in the upper port area for allowing the access of the YAG head from the top.

In this configuration, a cooling pipe from the module is splitted into two pipes: one of them is

- 2 -

JAERI-Tech 96-035

led horizontally to the cooling system and another is extended vertically to the cryostat lid for

the pipe maintenance by the YAG laser system. A cask of the YAG laser system is located at

the top of cryostat and the processing head for welding/cutting is inserted from the end of the

pipe vertically extended. Figure 2.3 shows a schematic view of the cask desired for this

purpose. In the cask, manipulators are installed for handling/transporting shields and for

inserting/extracting the welding/cutting equipment. An upper crane in the cask is mainly for

carrying manipulators to assemble/remove the shield plug and the YAG processing heads. A

lower crane in the cask is for assembly/disassembly of the upper port of the cryostat and

vessel, including lip shield welding/cutting. Figures 2.4 and 2.5 show schematic views of

the cask layout for the YAG laser and power source. They are installed in the crane hall and the

distance should be minimized in terms of data acquisition. In order to operate the 4 sets of

systems at the same time, each cask is installed at 90 degree intervals. After the blanket

branch pipes are cut, the blanket modules are removed through the horizontal ports using in-

vessel manipulators and transporters.

Table 2.1 Specifications of the blanket cooling pipe

Main pipe

Branch pipe

Minimum radius of curvature

SS316L, 100A, thickness of 6 mm

SS316L, 50A, thickness of 3 mm

400 mm

3. A PROCESSING HEAD OF YAG LASER SYSTEM

3-1. Constitution of Processing Head

According to the Industrial Standards in Japan, a permissible inside diameter of a 100A

stainless pipe is from 99.66 to 104.94 mm, so that the processing head has to be fabricated

within this range. Figure 3.1 shows the fabricated YAG laser processing head and Figs.

3.2, 3.3 and 3.4 show structural design of the welding/cutting processing head. This

system is composed of four vehicles and their external diameters are below 97 mm. The main

components of this system are optical fiber, lens and mirrors for the laser transmission, flexible

shafts and motors for drives, and sensors for positioning.

(1) Optical transmission mechanism

This is to transmit the YAG laser beam from the external source. The optical fiber

is made of synthetic quartz to tolerable for radiation hardness and covered by the

flexible tube which is also used to supply assist and shield gases for the

welding/cutting processes. Figure 3.5 shows a schematic view of the transmission

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JAERI-Tech 96-035

tube. Total length of the optical fiber is 20 m and the core diameter is 0.6 mm. In

order to reflect and focus the laser, lens and mirror are installed in front of the fiber.

Lenses are made of synthetic quartz and mirrors are made of OFHC, which are also

chosen in terms of radiation hardness.

(2) Drive mechanism

Since accurate positioning of the processing head within the range of 0.1 mm is

required for welding by YAG laser, this system is designed to have 5-axes freedom,

which are Z, 9, R, p and L axes as shown in Fig.3.2. Due to the space constraint

and minimum curvature requirement, the system is divided into 4 vehicles and driving

mechanisms are installed in the separated vehicles(No.2 and No.3) from the power

station vehicles(No.l and No.4): These vehicles are connection links in order to

transmit the driving forces. The major specifications of the driving mechanism of each

axis are described below.

1) Zaxis

Movement direction : movement of for fine adjustment of the processing

head along the axis of the manifold

Allowable stroke : 22 mm

Movement speed : 30 mm/min

The driving power is transmitted using a flexible shaft from the power station

vehicle(No.4) to the Z axis movement mechanism composed of a ball screw.

2) 9 axis

Movement direction : rotation of the processing head around the axis of

the manifold

Rotation angle : ±185 degreeRotation speed : 3.9 rpm ( adjustable)

The 9 axis rotation mechanism is installed in the No.2 vehicle which is

connected to the processing head with the universal joint. The driving power is

transmitted from the No.l vehicle using a flexible shaft.

3) R axis

Movement direction : telescopic movement of the welding/cutting nozzle

into a branch pipe axis

Allowable stroke : 34 mm

Movement speed : 942 mm/min (adjustable)

When the nozzle is fully extended into the branch pipe, the maximum distance

from the center of the manifold to the welding/cutting point is 77 mm. On the

contrary, the minimum distance is 69 mm, as shown in Fig.3.6. As a result,

in this system, the allowable processing range is 8 mm along the branch pipe

axis. However, it can be increased up to 29 mm by modifying the R axis

telescopic mechanism.

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JAERI-Tech 96-035

4) p axis

Movement direction : rotation of the welding/cutting nozzle around the

axis of the branch pipe

Rotation angle : ±185 degree

Rotation speed : 15 rpm (adjustable )

The driving power is transmitted from the power station vehicle(No.4).

5) Laxis

Movement direction : movement of the vehicles along the axis of the

manifold

Movement speed : 1 m/min

(3) Sensors for detecting the position of a branch pipe

Two sensors for detecting the position of a branch pipe are installed at 180 degree

intervals in the processing head. Eddy current type sensors are chosen due to its

compactness and precision. By rotating the processing head around the axis of the

manifold, the edge of a branch pipe can be detected while the head moves along the

manifold. In this way, the position of the processing head can be measured to the

branch pipe to be welded/cut. Guide rollers are installed near the sensors in order to

protect them from the corner edge of a branch pipe.

(4) Centering mechanism

Centering mechanisms based on air cylinder are installed in the No.2 and No.3

vehicles in which the processing head and the 9 axis rotating mechanism are installed.

Three air cylinders are arranged on the welding/cutting processing head and can be

contacted to the internal surface of the manifold so as to adjust the center of the head to

the manifold axis. In the case of the 0 axis rotating mechanism, three air cylinders are

also arranged in parallel to the manifold axis.

3-2. Performance Tests of Processing Head

In order to verify the basic functions and characteristics of the fabricated YAG laser

system, the processing head for welding/cutting has been tested and the results are as follows:

(1) Movement in cooling pipes

In this test, a straight pipe with length of 1000 mm and a bend pipe with a curvature

of 400 mm are prepared. They are stainless steel 316L 100A pipes with external

diameter of 114.3 mm and thickness of 6.0 mm. The processing head was repeatedly

inserted/removed into/from these pipes.

As a result, we confirmed that the processing head can smoothly move through

pipes and the required push/pull loads are only 5 kg .

(2) Driving mechanisms

JAERI-Tech 96-035

All driving mechanisms except the L-axis were tested to verify the allowable

movement stroke, rotation angle and operation speed. The results are summarized in

Table 3.1 and it is concluded that the driving mechanisms can be operated

satisfactorily and their operation ranges meet the design values.

(3) Centering mechanism

The movable strokes of the air cylinder type centering mechanisms are measured

and the operational range is confirmed to be the same as the design value, as listed in

Table 3.2.

Table 3.1 Test results of each mechanism movement

Test items

Range of

movement

Speed test

Axis of movement

0 axis

Zaxis

p axis

Raxis

9 axis

Zaxis

p axis

Raxis

Design value

±185 degree

22 mm

±185 degree

34 mm

3.9 rpm

30 mm/min

15 rpm

942 mm/min

Measurement result

Infinite rotation

21 mm

Infinite rotation

33 mm

3.91 rpm

30.0 mm/min

15.0 rpm

944.2 mm/min

Table 3.2 Test of the centering mechanism

Test items

Centering test

Cylinder

Welding/cutting

head

8 axis drive

mechanism

Design value

6 mm

8 mm

Measurement result

6 mm

8 mm

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JAERI-Tech 96-035

4. WELDING/CUTTING CHARACTERISTICS

As mentioned above, the welding/cutting processing head by YAG laser for the blanket

maintenance has been fabricated for branch pipe welding/cutting. In parallel with this

development, welding, cutting and rewelding tests have been conducted using the industrial 2

kW YAG laser system in order to qualify the welding, cutting and rewelding conditions,

including the effect of gaps.

Figure 4.1 shows the 2 kW YAG laser welding/cutting system utilized for the tests.

This system is composed of an optical fiber with a core diameter of 0.6 mm and a length of 20

m. The focal length of the lens system is 70 mm.

4-1. Basic Welding Test

In this test, the welding conditions were surveyed using SS316L plate samples with a

thickness of 3 mm as functions of laser power, welding speed, assist gas and gaps, as listed

below. The edge preparation of the samples was machined and the surface roughness is 1.39

(i.m in average and 8.45 |i.m in peak.

Laser power : 800,1000,1200 W

Frequency : 40 Hz

Duty : 50 %

Welding speed : 500, 700, 900 mm/min

Assist gas : Nitrogen, Argon, Helium

Gap quantity : 0, 0.1, 0.2, 0.3, 0.4, 0.5 mm

Work distance : 10 mm

Defocus distance : 0 mm

4-1-1. Dependency of laser power and welding speed

The dependency of laser power and welding speed on the welding quality has been

investigated. In this test, nitrogen with a blowing rate of 0.5 1/sec was used for the assist

gas and the butt weld without gaps was adopted. The following tests were performed for

the qualification; (1) appearance test, (2) radiographic test (RT), (3) macroscopic test, (4)

tensile test.

(1) Appearance and macroscopic tests

Figure 4.2 shows the results of bead appearance test as a function of welding

speed and laser power. In the case of the laser power of 800 W, the bead penetration

to the back surface was not observed at the welding speed of 700 and 900 mm/min.

Other cases have shown full penetration welding.

(2) Radiographic test (RT)

All samples welded satisfied the RT regulation( 1 st grade) and there was no

blowhole.

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JAERI-Tech 96-035

(3) Macroscopic test

Figure 4.3 shows the cross-section of welding penetration. It is found that

adequate welding conditions to satisfy the full penetration welding and welding

deposition are 500 mm/min at 800 W, 700 mm/min at 1000 W, and 900 mm/min at

1200 W.

(4) Tensile test

Tensile tests were carried out for all test samples welded. Figure 4.4 shows the

tensile test results. Tensile strength and elongation were remarkably decreased in case

of laser power of 800 W and welding speed of 900 mm/min due to less welding

penetration. In the case of 800 W and 700 mm/min, the elongation is decreased by

50 % composed with the base metal although the tensile strength is only 5 %

degradation.

4-1-2. Effect of assist gas

The effect of assist gas (nitrogen, argon and helium) on the weldability has been

investigated. In this test, the laser power and welding speed were fixed to be 1000 W and

700 mm/min, respectively. The following tests were performed for the qualification; (1)

appearance test, (2) radiographic test (RT), (3) macroscopic and microscopic test, (4) tensile

test.

(1) Appearance test

Figure 4.5 shows the appearance test results and all samples welded have

shown similar bead appearance.


In the case of helium gas, the welding quality is 2nd grade in the RT regulation.

On the other hand, the case of nitrogen and argon have shown the 1st grade in RT.

(3) Macroscopic and microscopic tests

Figure 4.6 and 4.7 show the cross-section of the welding penetration and the

micro structure, respectively. The welding deposition of all samples has similar wine-

cup type penetration although the width is slightly small in the case of helium.

(4) Tensile test

Tensile tests were carried out for all test samples welded. Table 4.1 shows the

tensile test results. Tensile strength and elongation of all samples are similar and the

elongation is decreased by around 25 % compared with the base metal.

JAERI-Tech 96-035

Table 4.1 Results of tensile tests

Assist gas

Nitrogen

Argon

Helium

Base metal

Tensile strength (MPa)

590

596587

585

Elongation (%)

40.1

40.7

38.9

54.1

4-1-3. Effect of gaps

The dependency of gaps at the edge preparation on the welding quality has been

investigated. In this test, the gaps ranging from 0 to 0.5 mm were examined under the

conditions of 1000 W laser power and 700 mm/min welding speed. The following tests of

all samples were performed for the qualification; (1) appearance test, (2) radiographic test

(RT), (3) macroscopic test, (4) tensile test.

(1) Appearance test

Figure 4.8 shows the appearance test results except the case of 0.5 mm gap

which would not be welded since the laser beam was penetrated through the gap.

Other samples have shown similar bead appearance.


All samples except the case of 0.5 mm gap satisfied the 1st grade in the RT

regulation and there was no blowhole.

(3) Macroscopic test

Figure 4.9 shows the cross section of welding penetration and a wine cup type

penetration was observed. In the case of 0.3 mm gap, however, the bead on the

backside is not appeared and the case of 0.4 mm gap has clearly shown the under cut

penetration.

(4) Tensile test

The tensile test results are shown in Table 4.2 and Fig. 4.10. The tensile

strength and elongation are decreased with increasing of gap. As a whole, the

maximum allowable gap for YAG laser welding without filler material is considered to

be around 0.2 mm from the tensile test results and the macroscopic tests.

- 9 -

JAERI-Tech 96-035


Gap (mm)

0.0

0.1

0.2

0.3

Base metal

Tensile strength (MPa)

590

586

560

549

585

Elongation (%)

40.1

38.3

32.1

30.4

54.1

4-1-4. Summary of welding tests

1) Optimum relation between laser power and welding speed

Table 4.3 shows the optimum relation between laser power and welding speed.

Table 4.3 Optimum relation between laser power and welding speed

Laser power (W)

800

1000

1200

Welding speed (mm/min)

500

700

900

2) Assist gas

In the case of helium gas, RT examination shows 2nd grade and welding

characteristics are inferior to other cases. In the case of nitrogen and argon, 1st grade

of RT is obtained. As a result, nitrogen gas is recommended for welding because the

number of porosity with a diameter of less 0.5 mm is few as compared with the case

of argon gas.

3) Allowable gap

A maximum allowable gap is estimated to be around 0.2 mm.

4-2. Cutting test

In this test, various of cutting conditions have been surveyed using SS316L plate

samples with a thickness of 3 mm. Cutting conditions of examined are as follows:

Laser power : 400, 600, 800 W -> Oxygen

800, 1000, 1200 W -> Nitrogen

Frequency : 40 Hz

Duty : 50 %

Cutting speed : 400, 600, 800 mm/min

- 1 0 -

JAERI-Tech 96-035

Assist gas : Nitrogen, Oxygen



4-2-1. Cutting test with the assist gas of Oxygen

The dependency of laser power, cutting speed and quantity of assist gas on the cutting

characteristics has been investigated using assist gas of oxygen. The following items were

measured for the qualification; (1) cutting surface, (2) cutting width, (3) dross and spatters,

(4) roughness of surface, (5) hardness of thermal effect part.

(1) Cutting surface

Cutting tests were carried out under various conditions of laser power and cutting

speed were changed. It is found that in the case of laser power of 400 W and cutting

speed of 800 mm/min, quantity of dross is the least Under this cutting condition, the

effect of assist gas quantity examined from 0.50, 0.83, 1.17 to 1.67 1/min. As a

result, dross is the least with assist gas of 1.67 1/min and the cutting surface is shown

in Fig. 4.11.

(2) Cutting width

Table 4.4 shows the results of cutting width under various conditions of laser

power and cutting speed with assist gas of 0.83 1/sec. All cases except the case of 800

W and 600 mm/min have shown similar difference between maximum width and

minimum width.

The dependency of assist gas quantity on the cutting width has been also examined

under the conditions of 400 W and 800 mm/min. The results are shown in Table

4.5 and both of 1.171/sec and 1.671/sec minimize the cutting width.

(3) Dross and spatters

Table 4.6 shows the results of the dross height measured under various

conditions of laser power and cutting speed with assist gas of 0.83 1/sec. In the case

of 400 W laser power and 800 mm/min cutting speed, dross height is the lowest

which is 0.43 mm. In all conditions, spatters are splashed on to the back cover plate

and the smallest in the conditions of 400 W and 800 mm/min.

As for the quantity of assist gas, the lowest dross height of 0.29 mm is obtained in

the condition of 1.67 1/sec as shown in Table 4.7.

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JAERI-Tech 96-035

Table 4.4 Results of the cutting width in various conditions of

laser power and cutting speed with assist gas of Oxygen

Laser power (W)

400

600

800

Cutting speed (mm/min)

600

0.78

0.50

0.28

0.81

0.50

0.31

1.19

0.55

0.64

800

0.75

0.44

0.31

0.78

0.50

0.28

0.76

0.56

0.20

1000

0.74

0.38

0.36

0.72

0.44

0.28

0.75

0.49

0.26

Unit: mm, Upper: largest width, Middle : smallest width, Lower: difference

Table 4.5 Results of the cutting width under various quantity of assist gas

Cutting conditions

Laser power: 400 W

Cutting speed : 800 mm/min



Quantity of

0.50

0.69

0.44

0.25

0.83

0.75

0.44

0.31

assist gas

1.17

0.63

0.44

0.19

(I/sec)

1.67

0.63

0.44

0.19


Table 4.6 Results of the dross height under various conditions of laser power and

cutting speed with assist gas of Oxygen

Laser power (W)

400

600

800


600

0.55

0.77

0.86

800

0.43

0.63

0.67

1000

0.56

0.62

0.78

Unit: mm

- 1 2 -

JAERI-Tech 96-035

Table 4.7 Results of the dross height in various quantity of assist gas

Cutting conditions

Laser power: 400 W


Work distance :1mm


Quantity of assist gas (I/sec)

0.50

0.51

0.83

0.43

1.17

0.40

1.67

0.29

Unit: mm

(4) Roughness of cutting surface

Table 4.8 shows the results of roughness measurement of cutting surface under

various cutting conditions. In the case of 800 W laser power, the cutting surface

becomes coarse compared with other cases: this due to large heating energy.

Regarding with the quantity of assist, the roughness of cutting surface is not

influenced so much, as shown in Table 4.9.

(5) Hardness of cutting surface

Hardness near the cutting surface was measured and the results are shown in

Table 4.10 and Fig. 4.12. In this test, laser power of 400 W and cutting speed of

800 mm/min were fixed. As a result, the hardness becomes the same as the base metal

at least 1 mm distance from the centering surface.

Table 4.8 Results of the roughness measurement of cutting surface under various

conditions of laser power and cutting speed with assist gas of Oxygen

Laser power (W)

400

600

800


600

10.8

75.9

9.3

62.4

16.7

113.0

800

13.3

98.8

11.9

90.1

14.5

114.1

1000

13.6

87.5

13.3

95.7

15.6

119.9

Unit: urn, Upper: Ra, Lower: Rmax

- 1 3 -

JAERI-Tech 96-035

Table 4.9 Results of the roughness of cutting surface

in various quantity of assist gas

Cutting conditions

Laser power: 400 W


Work distance :1mm



0.50

11.1

81.5

0.83

13.3

98.8

1.17

12.8

84.2

1.67

11.9

81.5

Unit: |i.m, Upper: Ra, Lower: Rmax

Table 4.10 Results of the hardness test

Cutting conditions

Laser power: 400 W




Distance fromcutting surface

(mm)

0.1

0.2

0.4

0.6

0.81.0

2.0

3.0

Hardness (Hv)

206

185

179152

158

149144

152

Hardness of base metal : 150 (Hv)

4-2-2. Cutting test with the assist gas of Nitrogen

The cutting characteristics are also investigated in the case of nitrogen assist gas. As a

function of laser power, cutting speed and quantity of assist gas. The following

measurements were performed for the qualification; (1) cutting surface, (2) cutting width,

(3) dross and spatters, (4) roughness of surface, (5) hardness of near the cutting surface.

(1) Cutting surface

Cutting tests were carried out under various laser power and cutting speed

conditions. In the case of laser power of 1000 W and cutting speed of 800 mm/min,

relatively good cutting surface was observed. On the other hand, cutting was

impossible in the case of laser power of 800 W and cutting speed of 800 mm/min.

The quantity of assist gas was varied from 1.25 to 1.67 1/min under the conditions of

- 1 4 -

JAERI-Tech 96-035

1000 W and 800 mm/min. As a result, quantity of dross is the least with assist gas of

1.671/min and the cross-sectional view of the cutting surface is shown in Fig. 4.13.

(2) Cutting width

Table 4.11 shows the results of the cutting width under various conditions of

laser power and cutting speed with assist gas of 1.67 1/sec. All results have shown

similar cutting width and the case of 1200 W and 800 mm/min indicates the minimum

width.

In addition, the cutting width is not significantly influenced by changing of assist

gas quantity, as shown in Table 4.12.

Table 4.11 Results of the measured cutting width under various conditions of

laser power and cutting speed with assist gas of Nitrogen

Laser power (W)

800

1000

1200

400

0.75

0.47

0.28

0.75

0.50

0.25

0.69

0.47

0.22


600

0.75

0.50

0.25

0.69

0.49

0.20

0.72

0.43

0.29

800

-

-

0.66

0.43

0.23

0.66

0.50

0.16


Table 4.12 Results of the measured cutting width in various quantity of assist gas

Cutting conditions

Laser power: 1000 W





1.25

0.63

0.44

0.19

1.67

0.66

0.43

0.23


(3) Dross and spatters

- 1 5 -

JAERI-Tech 96-035

Table 4.13 shows the results of the dross height measured under the various

conditions of laser power and cutting speed with assist gas of 1.671/sec. In the case

of 1000 W laser power and 800 mm/min cutting speed, dross height is the lowest

which is 2.29 mm. In all conditions, spatters were splashed on to the back cover

plate, and the quantity of spatter was smallest in the condition of 1000 W and 800

mm/min.

Regarding with the quantity of assist gas, similar dross height was observed in

both conditions of 1.25 1/sec and 1.67 1/sec, as shown in Table 4.14.

Table 4.13 Results of the dross height under the various conditions of laser power

and cutting speed with assist gas of Nitrogen

Laser power (W)

800

1000

1200


400

2.46

2.39

2.34

600

2.73

2.81

2.71

800

-

2.29

2.37

Unit: mm

Table 4.14 Results of the dross height in various quantity of assist gas

Cutting conditions

Laser power: 1000 W





1.25

2.17

1.67

2.29

Unit: mm

(4) Roughness of cutting surface

Table 4.15 shows the measured roughness of cutting surface under the various

conditions of laser power and cutting speed. In the case of 1000 W laser power,

cutting surface was relatively smoother compared with others.

Table 4.16 shows the effect of assist gas quantity on the surface roughness and

the roughness is slightly increased with increasing the flow rate.

(5) Hardness of near the cutting surface

- 1 6 -

JAERI-Tech 96-035

Hardness near the cutting surface was measured and the results are shown in

Table 4.17 and Fig. 4.14. As the result, it is found that hardening due to the laser

cutting reaches to 1 mm depth from the cutting surface.

Table 4.15 Results of the measured roughness of cutting surface under various

conditions of laser power and cutting speed with assist gas of Nitrogen

Laser power (W)

800

1000

1200


400

10.9

91.0

6.9

48.9

11.6

104.5

600

9.2

66.7

7.4

48.9

10.1

77.8

800

-

8.7

61.6

8.2

48.3

Unit: |im, Upper: Ra, Lower: Rmax

Table 4.16 Results of the measured roughness of cutting surface

under various quantity of assist gas

Cutting conditions

Laser power: 1000 W





1.25

5.5

55.6

1.67

8.7

61.6

Unit: jxm, Upper: Ra, Lower: Rmax

- 1 7 -

JAERI-Tech 96-035

Table 4.17 Results of the hardness test

Cutting conditions

Laser power: 1000 W

Cutting speed : 800 mm/mtn

Work distance :1mm


Distance fromcutting surface

(mm)

0.1

0.2

0.4

0.6

0.8

1.0

2.0

3.0

Hardness (Hv)

203

200

180

169

161152

150

150

Hardness of base metal: 150 (Hv)

4-2-3. Summary of cutting tests

From these test results mentioned above, the following cutting conditions should be

adopted:

1) Assist gas with oxygen

Laser power

Cutting speed

Quantity of assist gas

400 W

800mm/min

1.671/sec

2) Assist gas with nitrogen

Laser power

Cutting speed

Quantity of assist gas

1000 W

800mm/min

1.671/sec

Following rewelding tests mentioned below were carried out using these samples.

4-3. Rewelding test

To verify the reweldability of the laser cutting surface, rewelding tests were performed

under the following conditions. In this test, the laser cutting samples with assist gas of oxygen

and nitrogen were welded to SS316L plates with machining surface. The surface roughness of

the laser cutting samples were measured prior to the rewelding test and the results are presented

in Table 4.18. After the rewelding tests, bead appearance, X-ray inspection, microscopic

structures and tensile properties were measured for the welding qualification:

- 1 8 -

JAERI-Tech 96-035

:1OOOW

:40Hz

:5O%

: 700 mm/min

: Nitrogen, 0.5 1/sec

: 1 mm

: 0mm

Laser power

Frequency

Duty

Rewelding speed

Assist gas

Work distance

Defocus distance

(1) Appearance test

Figure 4.15 shows the bead appearance after the rewelding. Both samples cut

by oxygen assisted laser and nitrogen assisted laser have shown similar bead

appearance.


Both samples have shown the 1st grade in the RT regulation.

(3) Macroscopic and microscopic test

Figure 4.16 shows the cross-section of welding penetration. In both samples, a

wine cup type penetration was obtained and the nitrogen assisted laser cutting sample

indicates, a wide welding penetration compared with the oxygen assisted laser cutting

sample.

Microscopic structures of the welding joints are similar in both samples and

dendrite structures are observed, as shown in Fig.4.17.

(4) Tensile test

Tensile tests were carried out for both samples after rewelding. Table 4.19

shows the tensile test results and tensile strength and elongation of oxygen assisted

laser cutting samples are lower than those of nitrogen assisted laser cutting sample.

Table 4.18 Cutting surface of test pieces

Cutting conditions

Machining

Laser cutting with Oxygen

Laser power: 400 W


Quantity of gas : 0.83 I/sec

Laser cutting with Nitrogen

Laser power: 1000 W


Quantity of gas : 1.67 I/sec

Ra (urn)

1.39

13.3

8.67

Rmax (urn)

8.45

98.8

61.6

-19

JAERI-Tech 96-035

In this table, the tensile test results of a standard sample with machining surface are

presented as a reference case. Comparing with this reference case, the mechanical properties of

both laser cutting samples are slightly decreased but their degradation seems to be within the

allowable range. As a whole, rewelding of the laser cutting samples can be possible.


Combination

Machining

+ Machining

Machining

+ Oxygen cutting

Machining

+ Nitrogen cutting

Test

No.

1

2

3

Ave.

1

2

3

Ave.

1

2

3

Ave.

Tensile strength

(MPa)

590

593

588

590

578

579

575

577

587

589

586

587

Elongation (%)

40.7

40.4

39.6

40.1

31.2

30.8

29.2

30.4

39.6

37.2

37.2

38.0

RT level

1st

1st

1st

5. CONCLUSION

A YAG laser type processing head has been successfully fabricated and the applicability

to the blanket branch pipe welding/cutting has been demonstrated. In particular, this system

can be moved inside a 100-A pipe with a minimum curvature of 400 mm and the

welding/cutting nozzle with telescopic mechanism can be extended into a branch pipe with a

diameter of 50 mm for welding/cutting. In addition, this system is designed to have 5 axes

freedom so as to position the welding/cutting nozzle within the required accuracy for

welding/cutting. The centering mechanisms and position sensors are also facilitated for

positioning and fixation of the processing head. In parallel with this tool development,

welding/cutting/rewelding experiments using YAG laser have been performed to clarify the

optimum welding and cutting conditions including the effects of gaps and assist gas on the

weldability and reweldability. From these tests, the following conclusions are obtained:

- 2 0 -

JAERI-Tech 96-035

1) The optimum conditions of welding speed and laser power are 500 mm/rnin for 800

W, 700 mm/min for 1000 W and 900 mm/min for 1200 W.

2) A maximum allowable gap for welding is to be around 0.2 mm without filler

materials.

3) The optimum cutting conditions are 400 W / 800 mm/min in the case of oxygen

assisted cutting and 1000 W / 800 mm/min for nitrogen assisted cutting.

4) Rewelding of the laser cutting surface can be performed with keeping similar

mechanical properties to those of machining surface.

As the next development step, the following items are to be addressed:

1) Mock-up tests of the YAG laser processing head to demonstrate the total system

performance under the real pipe layout.

2) Possibility to increase the laser power for thick plate welding/cutting.

3) Establishment of rescue procedures.

4) Development of weld inspection and leak detection systems.

ACKNOWLEDGMENTS

The authors would like to express their sincere appreciation to Drs. M. Ohta, S. Matsuda,

M. Seki and S. Shimamoto for their continuous encouragement on this work. The

contributions by the staffs of department of ITER project and Toshiba Corp., are gratefully

acknowledged.

REFERENCES

[1] S.Matsuda, et al: Proc. 13th Conf. on Plasma Physics and Controlled Nuclear Fusion

Research, (Washington, 1990) IAEA-CN-53/G-2-2.

[2] K.Shibanuma, T.Honda, K.Satoh, Y.Ohkawa, T.Terakado, et al: Remote Maintenance

System Design and Component Development for Fusion Experimental Reactor, Proc. 16th

Sympo. on Fusion Tech., Vol.2, pp.l317-1321(1990)

[3] K.Honda, Y.Makino, M.Kondoh, K.Shibanuma: Feasibility Study of Internal-Access Pipe

Welding/Cutting System for Fusion Experimental Reactor(FER), Proc.LASER'91,(1991)

[4] K.Oka, S.Kakudate, M.Nakahira, et al: Critical Element Development of Standard

Components for Pipe Welding/Cutting by CO2 laser, JAERI Tech 94-033 (1994)

[5] M.Nakahira, K.Oka, S.Kakudate, , et al: Feasibility Study on YAG Laser System for

Cooling Pipe Maintenance, FTER Emergency Task Agreement JB-RH-1 (1993)

- 2 1 -

8000

ItoCO

I

Guide roller &Centerins mechanism

Power station(& Travel ins vehicle) /

Flexibleshaft

i

3

DetalI A

Fig. 1.1 Schematic view of the blanket maintenance Fig. 2.1 Schematic view of approachingthe blanket module

The insertion pipe for a processing head

I

Manipulator forcarr1ns shlelds

Manipulator for oarrlnswelding/cutting tools

LIP seal machine

Double-sealed door

Shi a Id Plug

>MSOi—<I

ft

CT51o

Fig. 2.2 Schematic view of the upper blanket pipe Fig. 2.3 A cask for the welding/cutting processing equipment

Laser andPower sour

DO

The caskithe b

forket Pi Pe

maintenancenap

Fig. 2.4 Cask layout for the blanket pipe maintenance(cross section)

Jhe cask for=^ the branket PiP-e

mai ntenance

2

2COOn

Fig. 2.5 Cask layout for the blanket pipe maintenance(top of view)

JAERI-Tech 96-035

CO

<

•8CD

CD

0.9-COCO0ooCtf

CD

0

CO

d

- 2 5 -

Movement range

R

Z

P

e

axis

axis

axis

axis

stroke

stroke

rotation

rotation

: 35 mm

:22 mm

:±185°

:±185°

No.1 vehicle

I082

Connection link

/ Centering mechanism

paxis No.4 vehicle

, ^ Branch pipe Main pipe

9 axis motor No.2 vehicle 9 axis z a x j s N o 3 v e n i c l e

Flexibleshaft

Universal Joint(processing head)

FlexibleR, Z, p axes motor

>2

i

o

Fig. 3.2 Schematic of YAG laser processing head

2nd Cu mirror

Sensorp axis

Nozzle

axis

Connection link

Centering e a x i s b e a r i n 9 Centering

mechanism j Optical fiber

\ „ p axis rotatingp axis mechanismbearing

Main pipe

0 axis rotatingmechanism

Flexible shaft Flexible shaft

1 st Cu mirror

0 axis drivenvehicle

Processinghead

io

Fig. 3.3 Inside structure of YAG laser processing head

>en2

T

ig. 3.4 Schematic of passing through a bending pipe (R400)

A

0°V

oOLO

-©-

AAssist gas

Optical fiber

A-A

sI

Ho

o

Transmission tube

Fig. 3.5 Schematic view of the transmission tube

JAERI-Tech 96-035

Noz

Main PIPe

Welding/cutting head

Iranch PIPe

Aval I able rangeof Processing

O)CO

N

Fig. 3.6 Available range of welding/cutting processing

-30

JAERI-Tech 96-035

(a) 2 kW YAG laser source

(b) Processing equipment

(c) Processing6 Heads

ooa=FOscillator

Focusing lens unit'Fiber

Df

(d) Schematic diagram of equipment

Fig. 4.1 YAG laser processing equipmentfor basic performance test

- 3 1

JAERI-Tech 96-035

Laserpower (W)

1000

1200


Laser surface

Back surface

Laser surface

Back surface

Laser surface

Back surface

Laser surface

Back surface

Laser surface

Back surface

Laser surface

Back surface

Fig. 4.2 Result of bead appearance testTest conditions

Test pieces

FrequencyDutyAssist gasWork distanceGap

:SS316L flat plate,thickness of 3 mm

: 40 Hz: 50 %: Nitrogen, 0.5 I/sec: 10 mm:0 mm

- 3 2 -

Laser power (W)

800

COoo

1000

1200


500

.-fCH

* « W . ~-

700 900

>tnVH

iOOen

Fig. 4.3 Macroscopic observation of weld part

105

0Q.

2Q.

95

90COo'c03

I 850

10

80

75

o 500 mm/min

- - • - - 7 0 0 mm/min

— a - - 900 mm/min

Normarized by virgin materialTensile strength : 585 MPa

800 1000Power (W)

Tensile strength

0

O

O"cCO

o

90

80

70

60

50

0 40

1 30* 20

Normarized by virgin materia!f Elongation : 54.1 %

500 mm/min

»»#»-7Q0 mm/min

-900 mm/min

800 1000 1200Power (W)

Elongation

Fig. 4.4 The relation between laser power and welding speedTest conditions

Test pieces : SS316L flat plate, thickness of 3 mmFrequency & duty : 40 Hz, 50 %Assist gas : Nitrogen, 0.5 I/secWork distance : 10 mmGap : 0 mm (butt welding)

m2!

nn

Assist gas (1/sec)

Nitrogen Argon Helium

0.50 0.50 0.83

CJ1

Laser surface Laser surface Laser surface

Back surface Back surface Back surface

Fig. 4.5 Result of bead appearance test with different assist gasTest conditions

: SS316L flat plate, thickness of 3 mmTest piecesLaser powerWelding speedFrequencyDutyWork distanceGap

1000W700 mm/min40 Hz50%10 mm0 mm

73

oen

Laser welding conditions

Assist gas (I/sec)

ICO

Laser power : 1000 W

Frequency : 40 Hz

Duty :50%

Welding speed : 700 mm/min


Gap : 0 mm


Welding joint : butt

>en2

i

oen

Fig. 4.6 Macroscopic observation of welding testwith different assist gas

Laser welding conditions Nitrogen , 0.50Assist gas (I/sec)

Argon , 0.50 Helium , 0.83

Ico

Laser weld part

Weid part Boundary part(Lower fig.) (Upper fig.)

Laser power : 1000W

Frequency : 40 Hz

Duty : 50 %





Gap : 0 mm

v j ' " '

'I*r^l>* -V^vw^rfw

0 s f f p

Nitrogen, 0.50 Argon ,0.5 ,0.83

„- ''if ^

' ' v t ' * * , * * * • { * , '

^ . ^ 2 "«. ! v t

i

sOn

Fig. 4.7 Microscopic observation of welding test with different assist gas

Laser welding conditions 0Gap (mm)

0.1 0.2

00I

Laser power : 1000W

Frequency : 40 Hz

Duty : 50 %


Assist gas : Nitrogen, 0.5 I/sec ;




Gap : 0 mm

.aser surface

Back surface

0.3

Laser surface

Back surface

t aser surface

Back surface

0.4

Back surface

Laser surface

Back surface

0.5

laser surface

Back surface

>mPC

i

Hn

ooen

Fig. 4.8 Result of bead appearance test with different gap

Laser welding conditions 0

Gap (mm)

0.1 0.2

i

Laser power : 1000W

Frequency : 40 Hz

Duty : 50 %


Assist gas : Nitrogen, 0.5 !/sec




rr>

0.3 0.4 0.5

impossible

sI

re

!COon

Fig. 4.9 Macroscopic observation of gap test

JAERI-Tech 96-035

0Q,O

CO

oCO

o

0

J5CD

110

100

90

80

70

60

50

n

i >,

Normali' TensileElongai

4s

|

zed by vstrengthion

L J

r~ i

5t

I ~-1

o Tensile strengtm Elongation (%)

(

rgin mat: 585 MF: 54.1 %

srial>a 1t

)

h(%)

- .

0 0.1 0.2Gap (mm)

0.3

Fig. 4.10 Result of allowable gap testTest conditions

Test pieces

Laser powerWelding speedFrequencyDutyAssist gasWork distance

SS316L flat plate,thickness of 3 mm1000 W700 mm/min40 Hz50%Nitrogen, 0.5 I/sec10 mm

- 4 0 -

JAERI-Tech 96-035

^

40 h n 6G ''--I 8G n K H Sfi 70

a) Laser surface b) Back surfaceA) Cutting appearance

4.0 S O 60 70 80

B) Cross sectionyssyyyyJ*yMryjMy4a<*yyZyZ&

Cuttina conditionsLaser powerCutting speedFrequencyDutyAssist gas

Work distance

:400W: 800 mm/min:40Hz: 50 %

1.67 I/sec ^^^^S^m,: 1 mm I l l l l l l l

90 *

rn m

Defocus distance : 0 mm C) Cutting width

Fig. 4.11 Cutting surface with assist gas of Oxygen

- 4 1

JAERI-Tech 96-035

C/3

0C

05

210

200

190

180

170

160

150

. » . • • , - . . - , . . .y -p .y .

# Weld part

Base metai

•\ A C \ F . L . I . . . J • i i . . . ; . . . • f I i • ' • * i i . ' < \ > , ? t, > J ..••' J L i • * . i A i i

0 0.5 1 1.5 2 2.5 3 3.Distance from cutting surface (mm)

Fig. 4.12 Result of hardness teston Oxygen cutting surfaceTest conditions


est dTest pieces

Laser powerCutting speedFrequencyDutyAssist gas

400 W800 mm/min40 Hz

: 50 %: Oxygen, 1.67 I/sec


- 4 2 -

JAERI-Tech 96-035

M

i n n M^ !2° |; so i n n no 12c 130

a) Laser surface b) Back surfaceA) Cutting appearance

|lh'|J

Cuttina conditionsLaser power :Cutting speed :Frequency :Duty :Assist gas :

Work distance :Defocus distance

i j-':i \ - ]" * \-v \ P I I j i i i f H H i r n iinjiing0 ?o hu ^o 11 i l l

B) Cross section

1000 W ?*-? r

800 mm/min40 Hz jkjM50 % •Nitrogen, ^ - . JB ^ ^1.67 I/sec ^^^^•L ] ^ H | |1 mm ^H^^^^^^rt^^^M^^BBB!: 0 mm C) Cutting width

mm

Fig. 4.13 Cutting surface with assist gas of Nitrogen

- 4 3

JAERI-Tech 96-035

CO(/)

210

200 -

190 -

180 -

170 -

160 -

150

140

,.Sf,w

_ A..~ w

"M

m

• • • .

*

. . . .

, . , ,

# Weld part

— Base metal

, . , . r • > } i 1 1 1 1

-

0 0.5 1 1.5 2 2.5 3 3.5

Distance from cutting surface (mm)

. 4.14 Result of hardness teston Nitrogen cutting surface

Test conditionsTest pieces

Laser powerCutting speedFrequencyDutyAssist gasWork distance

: SS316L flat plate,thickness of 3 mm

:1000W: 800 mm/min:40Hz: 50 %: Nitrogen, 1.67 I/sec: 1 mm

- 44

JAERI-Tech 96-035

Oxygen cutti

Laser

3

Back

Combination

n^L+jTiachming_^

surface

• r

surface

Nitrogen cutting + machining

Laser surface

s

s

Back surface

Fig. 4.15 Result of bead appearance testof rewelding

Test conditionsTest pieces

Laser powerWelding speedFrequencyDutyAssist gasWork distance


:1000W: 700 mm/min:40Hz: 50 %: Nitrogen, 0.5 I/sec: 10 mm

- 4 5 -

IOS

Laser welding conditions

Laser power : 1000 WFrequency :40 HzDuty : 50 %Welding speed : 700 mm/minAssist gas : Nitrogen, 0.5 I/secWork distance :10mmDefocus distance : 0 mmWelding joint : buttGap :0 mm

CombinationN2 cutting + machining O2 cutting + machining

>

o0-1

Fig. 4.16 Macroscopic observation of rewelding test

I

Laser cutting conditions

Laser weld part

\Weid part Boundary part

(Lower fig.) (Upper fig.)

Laser power : 1000 W

Frequency : 40 Hz

Duty : 50 %



Gap : 0 mm



Combination

Oxygen cutting + machining

Oxygen cutting + machining

Nitrogen cutting + macnining

Nitrogen cutting + macnining

i

ft

Son

Fig. 4.17 Microscopic observation of reweiding test

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MPa!--10bar)

1

0.0980665

0,101325

1.33322 x 10"'

6.89476 x 10"'

kgf/cm'

10.1972

1

1.03323

1.35951 x 10 3

7.03070 x 10 '

a tm

9.86923

0.967841

1

1.31579 x 10"'

6.80460 x 10 '

mmHglTorr )

7.50062 x 10'

73S.559

760

1

51.7149

lbf/in'(psi>

145.038

14.2233

14,6959

1.93368 x 10 '

1

X

IV

¥1

It,•a

J( =10 'e rg )

1

9.80665

3.6 x 10*

4.18605

1055.06

1,35582

1 60218 x 10 "

kgf-m

0.101972

1

3.67098 x 10 s

0.426858

107,586

0.138255

1.63377 x 10 i0

kW- h

2.77778 x 10- !

2.72407 x 10"'

1

1.16279 x 10-'

2.93072 x 10"'

3,76616 x 10 ;

4,45050 x 10 "

calUtltt)

0.238889

2.34270

8.59999 x 10 s

1

252.042

0.323890

3.82743 x 10 •"»

Btu

9.47813 x 10 '

9.29487 x 1 0 '

3412.13

3.96759 x 10 '

1

1.28506 x 10" '

1.51857 x 10 "

ft • lbf

0.737562

7.23301

2.65522 x 106

3.08747

778.172

1

1.18171 x 10""

eV

6.24150 x 10"

6.12082x 10"

2.24694 x 10"

2.61272x 10"

6.58515 x 10-"

846233 x 1 0 "

1

»t

3 7

Bq

1

X 101"

Ci

2.70270 x

1

1 0 "

Gy

1

001

rad

100

1

C/kg

2.58 x 10"4

_ R

3876

1

1 cal - 4.18605 J( , , l W/J;

= 4.184 J ( » f f r "

4.1855 J (15 X '

^ 1 PS < iLfij )) i

- 75 kgf-m/s

-- 735.499 W

ISlit''iw

Sv

1

001

rem

100

1

<86tr 12 n 26

DEVEIOPIIENT OF iEyOTE BORE TOOiS FOR PIPE WELDIiG/CUTTWG BY YAG LASER

jaeri-tech 96-035

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