Introduction

Flexible Crawler for NDT Inspection

Non-destructive testing (NDT) encompasses a disparate range of techniques which are used to detect internal and surface defects such as cracks, voids, porosity, inclusions and corrosion and play a vital role in many industries to ensure the quality and safety of materials, products and structures. Major users of NDT are the automotive, aerospace, oil and gas, petrochemicals, power generation and offshore industries and while much testing is conducted manually, several NDT techniques may be automated and recent years have seen growing interest in the development of robotic systems. The use of NDT robots generally reflects difficulties or safety issues surrounding access to the component or structure under test. Some examples include liquid storage tanks, pipe-work and pipelines, ships' hulls, offshore structures and the insides of turbines. For these types of applications, wheeled, climbing or crawling robot has been developed.

Rapid inspection of large areas has been an ongoing challenge to the NDE community in these days. Field inspection using manual scanning is labor intensive, time consuming and subjected to human error. Effective field inspection requires a portable, user friendly system that can rapidly scan large areas of complex structures. In recent years, various portable inspection systems have emerged including scanners that are placed at selected locations and sequentially repositioned to fully cover the desired areas. As the technology evolves, crawlers would be developed to operate automatically and search for flaws on pipe line and storage tanks without a human interference. Since the introduction of microprocessors, various types of portable scanners were developed using such NDE methods as visual, eddy currents, ultrasonics, shearography, radiography and thermography. While most scanners have been dedicated to a single inspection method, there is an overall trend to combine the capability of more than one inspection method.
To overcome this problem of needing multiple scanners for different containers (piper, tanks etc.), we have designed one robotic scanner which can be used in various positions and scan various containers as well, pipes, tanks etc. We have designed a three wheel robotic crawl (Flexible crawler). This robotic design includes seventeen components and each component has been modeled in Solid Work 3D CAD Software and has been assembled completely. Each component is assembled with required constraints which will give suitable degree of freedom according to the application.

A proper design has been made for probe holder to hold different probes used in Non Destructive Techniques (NDT). Probes are different for different NDT techniques. Some examples for probes are conventional ultrasonic probes, phased array probes, EAAAT probes, Eddy current probes etc. The probe dimensions depend on the scanning method. For example, there is no use of any media for impedance matching for EAAAT and Eddy current testing. However, a couplant (water or gel, which is used in ultrasonic medical field) is needed for conventional ultrasonic and phased array NDTs. Hence a proper design is required for probe holder to fulfill this functionality when these probes have to be used.

A powerful magnetic wheel has been developed in house which will help this robot to stick on to ferrous material. This circumferential movement is possible on different diameter of the pipes

Claims:

We claim that "The Flexible Crawler" carries probes which can be used for scanning axial pipes in the pipelines. Also, it has the capability to climb vertical pipe, walls and move circumferentially. The main feature of this design is the flexibility of usage on different pipe line diameter ranges and tank walls.

1. We claim that this flexible crawler has Axial movement on pipes diameter ranges from 4 inch to 36 inch

2. We claim that this flexible crawler has Circumferential movement on pipes diameter ranges from 10 inch to 36 inch

3. We claim that this flexible crawler can climb pipes Axially on vertical pipes of
diameter ranges from 4 inch to 36 inch

4. We claim that this flexible crawler has Circumferential movement on vertical pipes of diameter ranges from 10 inch to 36 inch

5. We claim that this flexible crawler can move on wall in any direction (including cylindrical wall of a storage tank)

6. We claim that this flexible crawler is so designed to hold various probes such that it can use various NDT techniques like:

• TOFD (Time Of Flight Diffraction)

• Guided Wave

• Conventional UT (Ultrasonic Testing)

• ECT ( Eddy Current Testing)

• MFL (Magnetic Flux Leakage)

• HOMC (Higher Order Modes Cluster) Guided Wave

• PAUT ( Phased Array Ultrasonic Technology)

Details of the Design components Part 1: Centre joint part 1

Centre joint part 1 is the first component modeled in 3D CAD software and it is considered as the reference of preceding components to assemble each other. It can be named as female part of second component called Main Wing. Two revolute joints are made in this which will give degree of freedom for rotating main wing through this component and this feature helps to give different diameter arc between magnetic wheels, which is assembled with Main Wing. This is featured in Figure 1

Part 2: Main wing

Main Wins is the male part of Centre joint part 1 which can be rotated from 0 degree to 30 degree through the first component. The magnetic wheel assembly will assemble in the slot of the Main Wing and it can be linearly moved through this slide by 60 mm. This linear movement help to robot adjust the movement according to pipe diameter. This is featured in Figure 2

Part 3: Centre Joint Part 2

Centre Joint Part 2 is a prismatic joint that will be permanently assembled to Centre Joint Part 1. This Prismatic joint helps the Main Wing to Drive Part 1 component to move linearly through this component. This movement helps this design to keep a permanent shape to keep center of gravity in a line when it use either on pipe or wall. This is featured in Figure 3

Part 4: Main Wing to Drive Part 1

This component will act as a link to connect the front magnetic wheels assembly to drive magnetic wheel assembly, so this is can act as a transferring medium to transfer rotary motion from drive magnetic wheel to front wheel magnetic wheels. This component will act as a hand grip also since it is cylindrical in shape and the center of gravity will lie in this axis of cylinder. This is featured in Figure 4

Part 5: Main Wing to Drive Part 2

Main Wing to Drive Part 2 is a small component which helps main wing to drive part 1 to assemble properly with the center joint part 2. It will also help to slide smoothly through slide of center joint part 2. This is featured in Figure 5

Part 6: Motor Wheel Support Part 2

It is a joint to assemble between Main Wing to drive part 1 and Motor wheel support part 1. This design of joint helps to slide as well as rotate on Main wing to drive part 1 so that it will give proper shape and balance depending on variable application in NDT. This is featured in Figure 6

Part 7: Motor Wheel Support Part 1

It is the main component for driving the Magnetic wheel, DC motor and encoder. Two collars are made for assembling these three components and this complete
assembly of these three parts will connect to motor wheel support part 1. During weld inspection the driving wheel should shift from the weld area for smooth movement. This whole assembly can be shifted from center to either left or right position so that it can be used for weld inspection. This is featured in Figure 7

Part 8: Magnetic Wheel Support for Wing Part 1

Magnetic wheel is very critical in Flexible crawler design. This component is one of the parts of Magnetic wheel assembly which is attached to Main wing. This component can move linearly through the slot of the Main wing so that it can be adjusted according to pipe diameter. This is featured in Figure 8

Part 9: Magnetic Wheel Support for Wing Part 2

This component acts as a collar in which a small bearing will be inserted for movement of magnetic wheel. Magnetic wheel shaft will be inserted into inner diameter of bearing and this component will attach to Magnetic Wheel Support for Wing Part 1. This assembly can easily be disassembled since it is assembled temporarily by using small nuts and bolts. This is featured in Figure 9

Part 10: Motor Slide Fixture Part 4

This component helps to slide through Motor wheel support part 1 component for getting a shift from center line between two front wheels. This feature helps back wheel to make a shift from the weld so that it can easily scan welding of a pipe circumferentially. This is featured in Figure 10

Part 11: Motor Slide Fixture Part 2

Motor is assembled with this component and 1:1 gear ratio train is used to transmit rotation from motor to back wheel. This component is assembled with Motor slide fixture part 4. This is featured in Figure 11

Part 12: Motor Slide Fixture Part 3

This component is the opposite collar of Motor slide fixture part 2 collars to support magnetic wheel. These two collars use small bearings to help magnetic wheel for smooth rotation. This is featured in Figure 12

Part 13: Probe holder link 1

Probe holder is the critical part of this robot since it is used in NDT. This component is one of the parts that comprise the component of probe holder assembly. This probe holder assembly is made for HOMC ultrasonic testing with water and gel as couplant. A pressurized contact is needed between probe and work piece for getting better signals. A spring is used for getting this pressurized contact and this spring force is achieved by using reaction force in magnetic force in magnetic wheel. Probe holder link 1 can slide through Main wing component hence it is possible to circumferentially position the probe on pipe. This is featured in Figure 13

Part 14: Probe holder link 2

This component helps the probe hold a pressure on work piece by using a spring attached with this component and Probe holder link 3. This is featured in Figure 14

Part 15: Probe holder link 3

This component has three holes as shown in figure. One hole is for holding one end of the spring and another end will be held on by the Probe holder link 2 hole. Centre hole of this holder is for giving rotation with respect to Probe holder link 2. Last hole is a thread for holding the remaining probe holder link. This is featured in Figure 15

Part 16: Probe holder link 40 mm

This component's size depends on the probe type and size. This acts as the wrist of the robot's hand to hold the probe and it has the degree of freedom like yaw and pitch motion in robotics. This is featured in Figure 16

Part 17: Probe holder 40 mm

This component is using to hold the probe and it has pitch rotation with respect to Probe holder link 40 mm components. This is featured in Figure 17
Complete Assembly of Flexible Crawler in shown in Figure 18
The final assembly is shown in figure given below which include motor Encoder and Magnetic wheels. This flexible crawler includes two probe holders to use through transmission techniques in NDT.