Development of a Robot for Boiler Tube Inspection

Md. Hazrat Ali

, Temirlan Zharakhmet, Mazghzhan Atykhan, Adil Yerbolat and Shaheidula Batai

School of Engineering, Nazarbayev University, 010000 Astana, Kazakhstan

Keywords: Robot, Boiler Tube, Coal-fired, Electric Plants.

Abstract: The maintenance and inspection of large vertical or horizontal tubes in an autonomous manner is still an

unsolved issue. Existing techniques can traverse various types of surfaces but cannot measure inner cracks

in a long tube. However, most of these techniques are restricted by accuracy level, type of construction

material and cost efficiency. This research is mainly focused on the studies of various types of design

investigations related to the climbing robots for the inspections, and design and development of a new robot

to solve the existing problem in measuring various pipes diameter in petroleum industries. Based on the

existing prototypes, a new type of adhesion, locomotion, sensor mechanisms and a modernized design was

accomplished. The importance of this work is to prevent hazardous failures, which probably can be

determined through the on-site analyses of the tubes. At this point, it is a laborious, time-consuming and

dangerous process, which is performed by the human being. Finally, a climbing robot based on duct fan is

designed and developed as a prototype. The thrust force, provided by the fan, ensures that the robot is not

falling while the DC motors generate the motion. The ultrasonic sensor is chosen for the defect detection. It

generates a reference signal of a proper tube and compares it to the signals received from the defected tubes.

The preliminary design and development of the robot are done in SolidWorks software together with the

available components in the market.

1 INTRODUCTION

The aging issue of civil architecture consisting

bridges, tunnels, and manufacturing communications

that mainly apply metal structures, pipes, and tubes,

has been a significant research topic of structural

health monitoring (SHM). The failure of inspecting

and anticipating the SHM of these constructions may

contribute to severe tragedies, such as Santa Barbara

oil spill (Kolpack,1969). Thus, obtaining the routine

inspection data, and further investigation is an

essential tool to figure out the sustainability of this

infrastructure. Considering Kazakhstani plants,

despite ongoing development in the robotics field,

most of the methods used for inspection of metal

structures are accomplished manually or even worse,

left without any evaluation. The proposed solution

for this issue is the robot which can be controlled

remotely, which means that it reduces any risks

associated with reaching difficult-to-access zones for

plant workers. The electronic components of the

robot should be able to detect the defects of the

structural units. The regular inspection of the tubes

and other structures is going to decrease the chance

of failure occurrence on the plant. This preventive

measure is not costly while it precludes high

expenses from the system breakdown. It is very

challenging and expensive to examine surfaces,

which are difficultly accessible, such as vertical

tubes in coal-fired electric plants. Present technology

of manual inspection is time consuming, costly, and

regularly needs the application of large scaffolds,

influencing human safety issues. The solution for

this is considered to be automated investigation

process which can be provided by a robot. Even

though a significant advancement in the robotics

field, it is not still fully developed to work in the

field. The robot should be able to move in a vertical

and horizontal direction and be able to inspect the

tube. It means that there should be a unique

technique for the robot to climb up and down and

specific sensors that will provide an appropriate

assessment of pipelines conditions. The research

focuses on creating an inexpensive prototype for

external inspection of pipes and other structures. A

robot based on Arduino board makes the inspection.

The key working principle of the robot is that it uses

ultrasonic sensor and camera to evaluate the health

534

Ali, M., Zharakhmet, T., Atykhan, M., Yerbolat, A. and Batai, S.

Development of a Robot for Boiler Tube Inspection.

DOI: 10.5220/0006930205340541

In Proceedings of the 15th International Conference on Informatics in Control, Automation and Robotics (ICINCO 2018) - Volume 2, pages 534-541

ISBN: 978-989-758-321-6

of the structure. The duct fan is applied to attach to

the surfaces and move in vertical directions. There

are two separate power sources for the Arduino and

duct fan as the duct fan requires more voltage to

work. The approximate cost for the prototype

development is $300, and the size is 250 mm x 250

mm x 100 mm.

2 LITERATURE REVIEW

The most cost-effective and troublesome

components of electric power, chemical, and

operating plants, which cause large expenses during

unscheduled breakdowns, adjustment work, are

boilers. Every existence of cracked tubes contributes

to an emergency shutdown of the whole plant. Thus,

the regular inspection of boiler tubes is carried out to

assure the operational safety and forbid the leakage

of hazardous substances to nature. Generally, the

investigation is performed manually or automatically

(Vakhguelt, Kapayeva, and Bergander, 2017). A

wall-climbing robot for the nuclear power plant is

discussed by Briones, L. et al. (1994). A marine

vessel inspection robot based on the magnet is

designed and developed by Markus Eich and

Thomas Vogele (2011). A fuzzy controlled based

similar robot for pipe inspection is proposed by

Huang, H. P., et al. (2010). Another paper discussed

an automatic inspection of ship hull by a magnetic

crawler using a camera (Annalisa et al., 2017).

2.1 Manual Type of Pipe Inspection

and Its Limitations

Manual type of pipe inspection is very challenging

and costly to investigate surfaces, which are

problematically attainable, as well as vertical pipes

in coal-fired electric plants. Present manual

techniques are time-consuming and commonly need

the utilization of vast scaffolds, which negatively

affects human safety issues (Advanced Pipe

Inspection, 2018).

2.2 Robot based Pipe Inspection and

Its Limitations

2.2.1 Internal Pipe Inspection Robot

Immersed pipes, generally used for gas pipelines,

cannot be investigated as conveniently as above-

ground pipes due to the excavation and refilling

effort involved. Namely, the ground must be

excavated before the investigation to expose all sides

of underground tubes located at depth. Then, the

ground must be backfilled after finishing the

analysis. All this work consumes a sufficient amount

of time beyond the time needed for the specific

investigation. The internal inspection robot proposes

the community the advantages that less time and less

operational cost are needed for the work. Thus,

interior surface inspection technologies are rapidly

being developed. However, there are several

problems with the interior surface investigation

performance of robots. Various limitations are

reported in the following paragraph (Kawaguchi et

al., 1995).

Figure 1: Manual inspection.

Problem 1: Robots operate in the most of the cross-

section of the pipe. Objects are standing in tubes, as

the plug valves, are challenging to handle for robots.

Robots usually cannot be driven through pipes of

certain types of diameters connected using reducers

or go through narrow paths, as valve position.

Problem 2: One of the most significant limitations

is that the supply, such as gas, hot water, which is

transferred through the conduits, is needed to be

switched off during pipe investigation. The

interruption not only adversely affects the

economics but also poses the risk of explosions due

to the interior of the tube is exposed to outside air.

2.2.2 External Pipe Inspection Robot

External climbing robots became more and more

significant in the engineering industry over the last

twenty years. The area of utilization of these robots

increases with their capability to traverse on

different surfaces and to operate faster and more

detailed. Currently, climbing robots are examined to

support the investigation, maintenance and building

tasks everywhere due to new locomotion types and

adhesion principles. One of the main aspects is

safety, which considers the ability of robots to

inspect dangerous constructions of human beings

Development of a Robot for Boiler Tube Inspection

535

(Schmidt and Berns, 2018). To perform the

requested tasks, climbing robots as all other

technical systems have to accomplish several

fulfilments which depend on the area of application.

However, commonly accepted requirements can be

figured applicable for practically all climbing robots

in the range of investigation and support:

a) Velocity and Mobility: The robot velocity and its

capability to move are two principal features in this

area. Based on the size of the piping construction it

might be obligatory to reach relatively high speed

even in vertical or horizontal direction. Furthermore,

it might be required to precisely manipulate and

position the system sidewards to investigate and

measure existing defects in the whole area of the

structure in 360

b) Payload: Based on the sensor type, locomotion,

as well as adhesion mechanisms, the vehicle needs

to be able to carry a payload of various weights.

c) Reliability and safety: Another significant non-

functional aspect is the robustness of the system. If

the tube-climbing robot fails during investigation

task, it would not be applicable in practice. Thus, the

reliability and safety requirements consist of robust

hardware, more advantageous controllers and

approaches to identify and take care of dangerous

situations and to rescue from them. Entirely, it might

be designated by rules to protect the robot within a

cable or wire to defeat the risk of a drop-off that

could hurt persons and destroy the system.

c) Reliability and Safety:

Another significant non-

functional aspect is the robustness of the system. If

the tube-climbing robot fails during the investigation

task, it would not be applicable in practice. Thus, the

reliability and safety requirements consist of

powerful hardware, more advantageous controllers

and approaches to identify and take care of

dangerous situations and to rescue from them.

Ultimately, it might be designated by rules to protect

the robot within a cable or wire to defeat the risk of

a drop-off that could hurt persons and destroy the

system.

d) Usability: Each of the abovementioned criteria is

significantly essential; however, this is only the

basis of the universal operability of the system. To

carry a vehicle system into operation, it has to be

more forceful, more efficient and less unsafe than

conventional methods, e.g., regarding inspection

systems. Moreover, it must be able to carry different

payloads (e.g., sensors or camera) depending on the

desired response, high mortality parts need to be

quickly replaceable, and the process must be faster

and less complicated compared to actual

technologies or methods.

By the performing task, a robot developer has to

determine which fulfilments have to be executed and

select applicable locomotion and adhesion

mechanisms.

2.3 Locomotion Types

a) Arms and Legs: The most general principle of

locomotion in the sphere of designing climbing

robots is the application of arms or legs. Based on

the specific type of task, climbing robots have been

constructed with the specified amount of limbs of

different degrees of freedom. The principal

advantage of this principle is high adaptability of a

robot to the surface structure. Every leg is designed

with adhesive components which allows an

examination of the foothold for the chosen attraction

forces. However, a significant amount of degrees of

freedom contributes to a complex mechanical

structure and control system. Also, this leads to

more considerable weight and greater torques.

Principally, the speed of these machines is

sufficiently low in consideration of other locomotion

mechanisms.

b) Wheels and Chains: For the operation on a

relatively smooth area, dozens of climbing robots

exist applying wheels or chain-driven locomotion. In

contrast to the legged systems, the adhesion and

locomotion components are decoupled in many

cases as used in different wheeled and tracked

machines. Another set of systems combine

locomotion and adhesion systems in the form of

electro adhesive or sticky tracks, tracks equipped

with suction cups or by magnetic wheels. The

significant advantage of wheeled or tracked

locomotion is the high speed, continuous movement

and the more straightforward mechanical design and

control elements. Nevertheless, these robots cannot

handle more substantial steps or obstacles, so they

are less adaptable to the surface characteristics and

are revealed to slip effects.

c) Sliding Frame: Particularly in combination with

pneumatic or magnetic adhesive systems sliding

frames are generally known. These principles

present a simple mechanical construction with two

frames which can move in a linear or rotational road

ICINCO 2018 - 15th International Conference on Informatics in Control, Automation and Robotics

536

against each other. Mainly, each frame is equipped

with a group of attach points like suction cups or

magnets and keeps the robot at the wall while the

second frame is ascended and moved in the desired

direction. It allows easy control of robot movement

in combination with reliable adhesion since the

method can test its foot points before lifting the

second frame. The disadvantages of this principle

are a low speed compared to wheeled or tracked

robots, a discontinuous movement due to the stick-

move-stick-move cycle and comparably large size.

Wires and rails: Rails and wires are widely used for

robot locomotion in some fixed operation types. The

essential advantage of these motion principles is that

the system is attached and cannot fall away since the

adhesion system only has to arrange the machine at

the construction while the wires carry the weight of

the vehicle and additional payload. It allows a much

simpler robot structure, but, of course, requires

remote control and equipment limiting the robot to

this particular setup.

2.4 Adhesion Principles

Similar to the type of locomotion. Also, the adhesion

mechanism has to be determined based on the

intended goal. This part explains various adhesion

principles, which include the following methods.

a) Magnetic Adhesion: This fundamental technique

for climbing robots includes electromagnets and

permanent magnets, which are placed on the surface

or held at a specific distance. This method is very

reliable on ferromagnetic structures, and it can

produce high adhesion forces on a limited surface

area. Some examples are given in Fig.2.

Figure 2: Magnetic robots (Schmidt and Berns, 2018).

b) Pneumatic Adhesion: The second principle is

the pneumatic or negative pressure adhesion

technique, which is categorized by three distinct

types: passive suction cups, suction chambers, and

vortex or thrust systems. Pneumatic adhesion types

of robots are shown in Fig.3.

Figure 3: Pneumatic adhesion robots.

Table 1 demonstrates the evaluation procedure of the

sensors discussed. Laser sensor has the highest range

and lowest percentage of error. However, it costs

correspondingly high. Also, it cannot penetrate

layers of the boiler tube. Infrared sensor has a small

range of operation and error, but this sensor depends

on the reflection characteristics of the object.

Ultrasonic sensor has a preferable range of working

and error. However, the received signal may be

fluctuated depending on environmental conditions.

Thermosensors are installed in these sensors to

compensate for the fluctuating. Overall, by

evaluating all type of sensors, it is decided to use the

ultrasonic sensor in the research due to its ability to

work under required conditions, cost-effectiveness

and a low percentage of error.

Table 1. Evaluation of sensors.

Sensors Range(m)

Error

(%)

Limitations

Cost

($)

Ultrasonic 0.2-10 2.2 – 3.4.

Depend on

environmental

conditions

2-20

Infrared 0.1-0.8 0.5-5.3

Depend on

reflection

arameter of the

object

2-20

Laser 0.2< 0.50%

Cannot penetrate

layers of tube

50-150

3 DESIGNS AND MODELING

3.1 The Concept

As it was mentioned above the primary goal of the

research is to design a robot for boiler coal-fired

tube plants, which satisfies specific objectives,

namely,

a) Move vertically and circular directions

b) Crack detection

c) Decrease time of inspection

d) Improve cost-resource efficiency

Development of a Robot for Boiler Tube Inspection

537

First of all, to make robot's movement towards the

corresponding directions, the principle of inspection

is specified. Because inside inspection requires

specific conditions, such as stopping production and

specific dimension of the robot for different tube

sizes, which are expensive and time-consuming,

outside inspection method is chosen. Consequently,

to perform outside inspection, adhesion principle,

specifically duct fan-based, is the most appropriate

method. Thrust force, which is created by duct fan,

is crucially needed to move vertically up and

circular directions. Secondly, because in recent

industry inspections in tube plants are mostly

performed by professionals manually, the

development of this robot automates the

investigation procedures, which in turn leads to

significant reduction of time consumption. As it was

mentioned above, the main time-consuming element

of the manual inspection is the human factor.

Generally, reduction of productivity and existence of

errors make the human resources time-consuming

component. In contrast, fully automated robots with

a certain amount of sensors can perform inspections

at any time and conditions without disruption of

productivity. Additionally, automation of

inspections leads to decreasing and elimination of

errors. The climbing robot works with a certain

amount of sensors to inspect tubes for cracks and

defects to achieve the third goal. Selection of sensors

with appropriate performance is an essential part of

tube inspection. Ultrasonic sensors are selected

because of its working range, low percentage of

error and cost-effectiveness. Additionally, as the

robot inspects only outer diameter of a tube, a

camera can be used as an alternative solution.

Figure 4: Final 3D Model.

Lastly, the implementation of climbing robots in

industry significantly reduces cost and improves

resource efficiency. In addition to the low cost of

components, robots do not require extra usage of

apparatus during the inspection. Furthermore, robots

can be reused for next inspections until it breaks.

However, it can be solved not by purchasing a new

robot, but replacing a broken component, because

the construction of robot is simple. Figure 4 shows

the final CAD model.

4 MATERIAL SELECTIONS

4.1 Components

The primary objective of this part of the paper is to

determine and describe the fundamental components

and their characteristics. Due to the chosen design,

electrical, mechanical and control components can

be designated. Tables 2 shows the critical

components incorporated into this research.

Table 2: Components.

Number Components Quantity

Arduino 1

Duct fan 1

3 ESC 1

Battery for duct fan 1

Battery for Arduino 1

Bluetooth module 1

Ultrasonic sensor 1

H-bridge 1

DC Motors 2

10 Wheels 4

Potentiometer 1

4.2 DC Motor Selection

It is needed to determine the angular speed and

required torque to select the appropriate motor to

drive the robot. Then compare results with the

technical specifications of the selected motor.

Figure 5. shows the incorporated DC motor to this

development and Eqns. (1) to (3) describe the

motor’s specification determination.

=/ (1)

=∗ (2)

=∗=∗



(3)

Where:  = angular velocity; V=desired speed

(assumed 10cm/s); r=radius of wheels (3cm);

T=torque; m=mass;

ICINCO 2018 - 15th International Conference on Informatics in Control, Automation and Robotics

538

=

.



0.03

3.3



32

 = 0.6 ∗ 15.5 = 9.3

 = 0.03 ∗ 9.3 = 0.2792.85 ∗ 

Based on equations 5 and 6, the applicable type of

DC motor with the  = 32 rpm or 3.3 rad/s and T =

0.2792.85 ∗  are selected.

Figure 5: DC Motor.

5 RESULTS AND DISCUSSIONS

5.1 Prototype

At the beginning of the research, the 3D model of

the robot was created in Solidworks. Then,

according to the design, the prototype was started to

construct. However, there were significant changes

in the design to improve the performance of the

robot. Since the main objectives of the construction

were to decrease the weight of the robot, excessed

materials were removed, and lighter materials were

selected. For example, at the beginning metallic

frame (Fig. 6) with appropriate locomotion were

ordered, but due to the weight of the robot, it was

not used.

Figure 6: Metallic frame.

Another objective was to increase adhesion. For that

purpose, several types of locomotion were

considered. At the beginning of the research the

locomotion with caterpillar belt was considered, as it

has the larger contacted surface area, consequently

has greater adhesion.

Figure 7: Final prototype-side view.

Figure 8: Final prototype-top view.

However, due to the delivery problem of the

procurement other types were considered. Therefore,

the locomotion with two driver and one guide

wheels were considered to decrease the weight of

the robot. However, by decreasing the weight of the

robot, adhesion was also decreased. As a result, it

was decided to use 4 wheels, specifically two drivers

and 2 driven wheels with two-sided tape to increase

adhesion. However, after the two-sided testing tape

was removed, it glued the robot to the wall. Another

method to increase the adhesion is to decrease the

clearance between the robot and the surface of the

tube. To achieve that several objective types of the

frame were constructed. From Fig. 7 it can be seen

that air suction area was decreased, but it did not

affect. Then, it was decided to decrease the full

clearance between the frame and the surface of the

tube, as can be seen in Fig. 8. There were two

primary objectives while assembling all above-

discussed components. First of all, it is needed to

make the robot move by controlling it through

Bluetooth module. It is required to connect the

motors to accomplish this task. Bluetooth module

Development of a Robot for Boiler Tube Inspection

539

and power supply to the Arduino. The Bluetooth

module is used. Thus, writing program is not

necessary. Secondly, it is required to build the

connection to make the robot climb vertically up and

move circular direction on the tube. To achieve this

objective duct fan system is added. First of all, duct

fan is connected to an ESC, which is connected to

Arduino and power supply, simultaneously.

5.2 Testing

Testing was performed to regulate the components

and optimize the performance of the robot. For

instance, the direction of the motors was determined

during the testing. Also, required the rotational

speed of the duct fan was regulated at appropriate

power to save the power of the battery. During the

test, an electrical component was damaged and

burned. Table 3 highlights the advantages of duct

fan used to develop this robot.

Table 3: Comparing with other methods.

Robot type

Main

Advantage

Main

Disadvantage

Duct Fan

The simple

and cheap

mechanism,

easy to build

a prototype.

Needs design

modifications

to work on

pipeline

inspection

Manual

Inspection

High accuracy

Cost, more

extended time

consumption,

the human

factor

Magnetic

crawler

Can be used

on iron

surfaces which

works in the

case of this

research

Can shear off

due to

obstacles and

heavy because

of the magnets.

Suction

mechanism

The simple

mechanism

can be applied

to irregular

surfaces

Does not suit

size limitations

Flight robot Fast

Risk of

breakdown

5.3 Working Principles

Cr-Mo tubes are used in Coal-Fired Electric plants

in Kazakhstan. About 80% of electricity in

Kazakhstan is produced from coal (Kegoc, 2018).

Therefore, coal-fired plants are significant for

energy supply for the country. Chromium-

Molybdenum is a type of 41xx steel which is used in

high temperatures and pressures operating

conditions. Even if it is the most appropriate

material for boiler tubes, it has some defects after

operating for a specified period. A failure of one

tube may cause many problems in the manufacturing

process. Orr et al. (1978) present a study of

Chromium-Molybdenum steels failure modes. They

discuss various factors affecting the defects

emergence. The most important factor while

studying Cr-Mo boiler tubes is the diameter of the

tubes because it makes a significant impact on size

limitation. The catalogues show that the tube

diameter may vary from 31.8mm to about 50cm.

According to Viswanathan (2005), the main steam

pipes are about 50cm in diameter. Therefore, the

robot should not exceed this diameter and be as

small as it is possible. Apart from that, the robot can

be found useful in a lot of other inspection

processes. For instance, if there is a need to check

something under the bridge, the robot can cope with

it, as the thrust force should be able to keep it upside

down. Therefore, this type of technique can be

applied in many fields where defect detecting plays

an important role. The main limitation for the

prototype is the curvature of the surface: it is too

high, the model is not capable of holding on the

space.

6 CONCLUSIONS

This research contributes to the field of tube

inspection in petroleum industries. There were two

main challenges: i) decide on tube climbing

technology, and ii) suggest a sensor system for

defect identification. For the first challenge, duct fan

based method was selected due to its effectiveness,

cost, and simplicity. It has enough trust force to hold

itself to the surface on a vertical wall. The cost of

the prototype does not exceed $300. Concerning the

second problem, the external inspection, which is

also significant to perform, is possible to accomplish

with the presented prototype. It uses the ultrasonic

sensor to measure the distance until the surface. The

reference signal shows the distance when the

exterior part is proper, i.e., without any defect. If the

ICINCO 2018 - 15th International Conference on Informatics in Control, Automation and Robotics

540

signal differs from the reference, it can be concluded

that that the surface has a defect. Moreover, one

more proposed alternative is to use the camera and

check the structure by observing the image of it.

Another area of application is various structures that

are subjected to risk of failures such as bridges,

tunnels, tanks, ships, walls, windows and ventilation

systems. Since the robot can work with the camera,

it can check any surface with appropriate curvature

for the defects. As some areas to inspect manually

can be challenging to reach, a robot should substitute

the human in those difficult to reach zones. In

conclusion, the key objectives of this research are

achieved; the prototype with the electronic and

mechanical components is built and tested. The

preliminary results of this work provide an excellent

framework for the future advancement in this field.

REFERENCES

Advanced Pipe Inspection. (2018).Non-Destructive

Testing (NDT) - Advanced Pipe Inspection. [online]

Available at: http://www.api-uk.com/api-services/ndt

testing/ [Accessed 22 Apr. 2018].

Annalisa Milella, Rosalia Maglietta, Massimo Caccia,

Gabriele Bruzzone, (2017) "Robotic inspection of

ship hull surfaces using a magnetic crawler and a

monocular camera", Sensor Review, Vol. 37 Issue:4,

pp. 425-435, https://doi.org/10.1108/SR-02-2017-

0021

Briones, L., Bustamante, P., & Serna, M. A. (1994, May).

Wall-climbing robot for inspection in nuclear power

plants. In Robotics and Automation, 1994.

Proceedings, 1994 IEEE International Conference on

(pp. 1409-1414). IEEE.

Eich, M., & Vögele, T. (2011, June). Design and control

of a lightweight magnetic climbing robot for vessel

inspection. In Control & Automation (MED), 2011

19th Mediterranean Conference on (pp. 1200-1205).

IEEE.

Huang, H. P., Yan, J. L., & Cheng, T. H. (2010).

Development and fuzzy control of a pipe inspection

robot. IEEE Transactions on Industrial Electronics,

57(3), 1088-1095.

Kawaguchi, Y., Yoshida, I., Iwao, K. and Kikuta, T.

(1995). Development of Internal Gas Pipe Inspection

Robot. Journal of Robotics and Mechatronics, 7(5),

pp.371-376.

Kegoc (2018). Kazakhstan Electric Power Industry Key

Factors | KEGOC. [online] Available at: http://

www.kegoc.kz/en/power-industry/Kazakhstan-elec..

[Accessed 22 Apr. 2018].

Kolpack, R. (1969). Movement of Oil and Water In

Santa Barbara Channel, California. International Oil

Spill Conference Proceedings, 1969(1), 341-341.

http://dx.doi.org/10.7901/2169-3358-1969-1-341.

Orr, J., Beckitt, F. R., & Fawkes, G. D. (1978). The

physical metallurgy of chromium-molybdenum steels

for fast reactor boilers. In Ferritic steels for fast

reactor steam generators. Proceedings of an

international conference held by the British Nuclear

Energy Society at the Institution of Civil Engineers,

London 30 May-2 June 1977.

Schmidt, D. and Berns, K. (2013). Climbing robots for

maintenance and inspections of vertical structures—A

survey of design aspects and technologies. Robotics

and Autonomous Systems, 61(12), pp.1288-1305.

Vakhguelt, A., Kapayeva, S. and Bergander, M. (2017).

Combination Non-Destructive Test (NDT) Method for

Early Damage Detection and Condition Assessment of

Boiler Tubes. Procedia Engineering, 188, pp.125-132.

Viswanathan, R., Henry, J. F., Tanzosh, J., Stanko, G.,

Shingledecker, J., Vitalis, B., & Purgert, R. (2005). US

program on materials technology for ultra-supercritical

coal power plants. Journal of materials engineering

and performance, 14(3), 281-292.

Development of a Robot for Boiler Tube Inspection

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