development of an automated-ultrasonic gauging system for ... · 89c51 rd2 microcontroller board...

Indian Society for Non-Destructive Testing Hyderabad Chapter

Proc. National Seminar on Non-Destructive Evaluation Dec. 7 - 9, 2006, Hyderabad

NDE-2006

Development of an Automated - Ultrasonic Gauging System for Tubes and

Pipes

V.H. Patankar1, V.M. Joshi

1 and B.K. Lande

2

1Electronics Division, Bhabha Atomic Research Centre, Mumbai-400 085 2Electrical Engineering Department, V.J.T.I., Matunga, Mumbai-400 019

e-mail: [email protected]

Abstract

Tubes/Pipes employed in critical applications such as Power Plants, Petrochemical

industry and others, demand very stringent quality control. Various Non-Destructive

Testing (NDT) techniques are used for inspection of such objects both during

fabrication as well as in-service stages. Ultrasonic testing (UT) is a very popular NDT

technique adopted in such applications. Flaw detection and thickness gauging are the

main UT methodologies adopted in such inspections. Today, ultrasonic imaging

systems are also available and such a system can be utilized for complete volumetric

inspection of the desired tubes/pipes. In flaw detection, the prime objective is

detection of internal flaws, if any, where as gauging enables high resolution thickness

and dimension measurements. Imaging systems basically provide both the operations, though gauging using imaging technique may not provide very high resolution. An

advanced system capable of both, B/C-Scan imaging and high resolution gauging of

tubes/pipes has been developed at Electronics Division, B.A.R.C. The system is based

around an Industrial Personal Computer and all the electronics hardware needed for

imaging and gauging has been developed at B.A.R.C. Extensive application software

– based on Visual Basic and Visual C++, running under Windows98 – has been developed to provide realize an advanced system suitable for tube/pipe inspection and

gauging. A two axes motorized mechanical scanner has been fabricated and it

provides automated inspection of tubes from inside using water immersion technique,

under the control of host PC. Initial trials have been carried out using Zircaloy and

Stainless Steel sample tubes with artificial defects. This paper highlights the hardware

and software features of the ultrasonic system and includes a discussion on the trial

inspections carried out with the system.

Keywords: Ultrasonic Imaging, Ultrasonic gauging, A-Scan, B-Scan, C-Scan,

NDT/NDE, Wall Thickness, Tube/Pipe

1. Introduction

In industry, Ultrasonic Inspection/

Imaging (UI) of tubes and pipes is carried

out to meet stringent Quality Assurance

(QA) demands particularly when the

inspected tubes/pipes are constituents of

strategic equipments or critical plants. To

perform quality checks on tubes, UI and

gauging are preferred techniques. The UI

technique enables the NDT experts to

perform flaw detection and sizing. Full

volumetric inspection of the tube needs to be

carried out in order to follow the “zero error”

concept for tubes. The UI method is complex,

time consuming, costly but is fully suitable

for volumetric inspection of tubes. On the

other hand, the ultrasonic gauging method

V.H. Patankar, V.M. Joshi and B.K. Lande

NDE-2006 220

provides information regarding the Wall

Thickness (WT), Inner Diameter (ID) and

Outer Diameter (OD) of the tube and the

variation therein due to stresses and

corrosion. The gauging method is precise,

fast, reliable and economical but internal

defects cannot be detected with it.

Generally gauging technique is used to

confirm the dimensional integrity of the

tube and the UI technique is employed at

suspected locations.

Gauging of tubes can be performed

using contact or water immersion method.

Pulse-echo technique employs the same

transducer as a transmitter and receiver of

ultrasound and using direct contact

method, tubes with smooth surface and

with access either from OD or ID side can

be inspected. Here, a couplant

(oil/water/grease) is essential for good

coupling of ultrasound to the tube under

inspection. Water immersion method is

mostly preferred for inspection and

gauging of tubes. The tube to be inspected

is immersed into the water and using the

immersion transducers, the desired

inspection is carried out either manually or

by automation, without wear and tear of

the transducer face.

2. Ultrasonic Gauging / Dimension

Measurement

Thorough inspection of tubes/pipes,

employed in Nuclear, Petrochemical

Industries, Defence and Aviation, is a vital

task. This may be carried out routinely

during Pre-Service, In-Service and Post-

Service Inspection schedules. Immersion

based Pulse-Echo technique is widely used

to carry out wall thickness gauging as well

as Dimension measurement for tubes and

pipes. Generally, high frequency, focused -

immersion transducers are needed for this

purpose. The tubes can be gauged using

water immersion technique in two ways as

indicated in Fig. 1 and Fig. 2. In method I,

the tube to be inspected is filled with water

with an access from inside and the

immersion transducers are placed 1800 apart,

each facing the ID of the tube. In method II,

tube is placed into a pool of water with an

access from outside only and the immersion

transducers are placed 1800 apart, each facing

towards the OD of the tube. Using

automation, the entire transducer assembly or

the tube itself can be rotated and indexed

linearly to gauge the entire tube under

inspection.

Transducer

TR1

Transducer TR2

ID = WP1 + WP2 + S

OD= ID + WT1 + WT2

S

Tube is filled with water

Fig. 1: Inspection of Tube from Inside

Tube is placed inside

a water pool

OD= S - (WP1 + WP2)

ID= OD - (WT1 + WT2)

TR1

TR2

S

Fig. 2: Inspection of Tube from Outside

For Fig. 1 and Fig. 2, WT1= Wall

Thickness measured by TR1 or a transit time

measured between the echo signals

corresponding to ID and OD of tube. WT2=

Wall Thickness measured by TR2 or a transit

time measured between the echo signals

corresponding to ID and OD of tube. WP1=

Water Path measured on TR1 side or a transit

time between the transmit pulse and the

interface echo reflected either from ID of tube

for Fig. 1 or from OD of tube for Fig. 2.

WP2= Water Path measured on TR2 side or a

transit time between the transmit pulse and

the interface echo reflected either from ID of

tube for Fig. 1 or from OD of tube for Fig. 2.

S= Face to face separation between TR1 and

TR2. [1,2].

Development of an Automated - Ultrasonic Gauging System

NDE-2006 221

8 - C h a n n e l U l t r a s o n ic P u ls e r -

R e c e iv e r U n i t M u l t ic h a n n e l S e q u e n c e r B o a rd B o a r d

A m p l i f ie r B o a rd

1 0 0 M S P S D ig i t i z e r B o a r d

P C B U S

In d u s t r ia l P C

S t e p p e r

M o to r C o n t r o l

a n d D r i v e

U n i t

R S 4 8 5

L IN K

Z - T h e t a

S c a n n e r

T R 1 T R 8

T

U

B

E

R X 1 R X 8 T R G 1 T R G 8 T R G

V O V m u x

L im it S w i t c h e s F o r Z A x is a n d

- S h a f t E n c o d e r s & P r o x im it y D e t e c to r s

F o r Z a n d T h e t a A x e s

T o p T a n k

B o t t o m

T a n k

Fig. 3: Block Diagram of Multichannel Ultrasonic Imaging System–ULTIMA

89C51 RD2 Microcontroller

Board

(100MHz) High

Speed Counter

Board (CH1)

(100MHz) High

Speed Counter

Board (CH2)

Ultrasonic Spike

Pulser - Receiver Board (CH1)

Ultrasonic Spike

Pulser - Receiver Board (CH2)

Industrial PC Controller

& Drive Unit For Z - Theta Scanner

RS 485 Link

RS232 - RS485 Converter

Sample Tube/Pipe

TG1

TG2

TRG1

TRG2

RX - 1

RX - 2

COM 3 COM 4

TX - 2 TX - 1

Water

TR2 TR1

Fig. 4: Block Diagram of an Ultrasonic Tube Dimension Measurement System - UTDMS


NDE-2006 222

Fig. 5: B-Scan Images (a) to (C) are acquired by UTDMS using Gauging Technique. And B-

Scan Images and corresponding A-Scan waveforms (d) to (f) are acquired by ULTIMA

100M8, using ultrasonic imaging technique

3. Ultrasonic Systems for Inspection and

Gauging of Tubes

The metallic tubes are inspected under

automation, by ultrasonic imaging

techniques using A-Scan waveform and B

or C-scan image mode for detection of

internal flaws/defects and sizing of

defects, if any. On the other hand, the

integrity of tubes can be confirmed by

ultrasonic gauging technique. Two kinds

of ultrasonic systems are available for

testing of tubes where, the first kind of

system can carry out ultrasonic imaging

for flaw detection and the second kind of

system can perform ultrasonic gauging for

confirmation of dimensional integrity. It

has been observed that, there is a need of

the industry to develop an integrated

system, which can perform both ultrasonic

inspection and gauging. In order to

perform an automated ultrasonic imaging

and gauging operation for tubes/pipes,

Electronics Division, BARC has

developed an advanced system, which

integrates the imaging and gauging

requirements. The gauging system is linked to

the imaging system by RS485 interface. Both

the systems are capable of operating in

standalone mode also. The overall system

configuration is -

1. Multichannel Ultrasonic Imaging System

ULTIMA 100M8 and

2. Ultrasonic Tube Dimension Measurement

System UTDMS

The block diagram of ULTIMA 100M8

system has been shown in Fig. 3. The

ULTIMA 100M8 system consists of PC Add-

on Boards - 1) 100MSPS, 8 Bits Digitizer, 2)

Multichannel Sequencer, 3) Low noise -

Programmable gain Amplifier and 4) 8-

channel ultrasonic spike pulser-receiver unit.

The system is based on the Industrial PC for

shop-floor inspection activities. The Win98

compatible, “Ultrasonic Tube Imaging

Software” (UTIS) has specifically been

developed for this system using Visual Basic

and VC++ (6.0). The system captures the RF


NDE-2006 223

echo signal in B/C-Scan imaging mode, in

synchronization with the ‘water-metal’

interface echo, for immersion mode. The B

and C-Scan cross-sectional images

respectively, are acquired and

reconstructed under automation and they

permit visualization and sizing of internal

defects. The ULTIMA 100M8 system’s

host PC communicates with the controllers

of a Z-Theta mechanical scanner, via

RS485 serial link. This scanner is

designed to inspect tubes from ID side.

With the help of eight immersion

transducers, mounted (45o apart) on the

inspection head, imaging of the selected

region of the tube can be performed, by

imparting linear and rotational movements

to the inspection head simultaneously.

[Ref. 4] The tube is held at both the ends

with the help of sealed jackets and the tube

and the jackets are filled with water during

testing.

The UTDMS is a two-channel tube

dimension measurement system, which is

based on 89C51RD2 micro-controller. The

block diagram of the UTDMS is shown in

Fig. 4. UTDMS consists of two PCBs

containing of High frequency ultrasonic

spike pulser – receiver and High-speed

counter for each transducer. The unit is

linked to the host PC via RS485 interface.

The firmware for the micro-controller is

developed using standard assemblers.

Win98 compatible data acquisition

software has been developed using VB 6.0

for the host PC. The UTDMS is capable of

measuring the wall thickness with 25

microns precision for Zircaloy tubes.

However, the ID and OD can be measured

with a precision of 100 microns. In

gauging also, the B-Scan view of the

selected region of the tube can be

synthesized by computing together the

values of WT, ID and OD and plotting

them over a full length of the tube.

Under automation, the ultrasonic tube

inspection and gauging is carried out by

ULTIMA 100M8 and UTDMS

respectively. For this purpose, a dedicated Z-

Theta mechanical scanner – has been

developed. The scanner enables the user to

test a metallic tube from inside, by ultrasonic

water immersion technique. The tube to be

inspected is clamped in the top and bottom

jackets. O-rings are used for obtaining a fully

watertight environment. Using a pump, the

tube is filled with degassed water. An

inspection Head carrying eight, line focused,

20MHz, immersion transducers are employed

to move the transducers in both rotary (Theta)

and linear (Z) directions with the help of two

stepper motors. The stepper motor controllers

are interfaced to host PC using RS485

protocol. Using +/- JOG, +/- Absolute MOVE

and +/- Immediate MOVE commands, the

inspection head can be positioned at desired

location in the tube. In both the inspection,

and gauging modes, the data acquisition is

always carried out when the transducer is

stationary. The B-Scan imaging is carried out,

by moving the inspection head along a single

axis (either in Z or Theta direction). The C-

Scan image acquisition is performed by a

combination of Z and Theta movements, for

covering the entire volume of the tube.

4. System Overview for UTDMS

Ultrasonic Tube Dimension Measurement

System has been configured in 4U x 19” rack

mounting format. This embedded system is

based on the Philips 89C51RD2 micro-

controller, and a multidrop interface for

stepper motor controllers and the host

computer, for automated data logging and

post acquisition analysis. As the UTDMS is

intended for precise dimension measurement

of Tubes, suitable automation has been

incorporated into the system. The hardware

constituents of the UTDMS are – 1)

89C51RD2 micro-controller board with

RS232 interfaces, 2) Ultrasonic Spike Pulser

and Receiver board (2 channels), 3) High

Speed counter board (2 channels), 4) RS232

To RS485 converter (commercially available)

module, 5) Host – Industrial computer with

two ports of RS485, 6) RS485 based 2-axes

stepper motor controller and drive unit; Z-

Theta mechanical scanner suitable for


NDE-2006 224

inspection of Tubes from ID side, under

immersion scanning mode; Ultrasonic

Inspection Head with facility to mount 8

nos. of immersion transducers; overhead

and bottom tanks with water pump for

closed loop water circulation.

The firmware for micro-controller

has been developed using standard

assembly tools of 89C51. The system

software, which runs on the Windows98

platform, has been designed with an

extensive GUI for user-friendly operation,

using VB (Ver. 6.0) to perform data

logging and analysis. The UTDMS

acquires and transmits the data with

appropriate headers, in response to the

command given by the host PC. The

stepper motor controllers have been

configured in closed loop mode with

associated feedback and safety elements.

Design details of the UTDMS are given in

the following sub sections.

4.1 89C51RD2 Micro Controller Board

Philips 89C51RD2 serves as the core

controller and controls the entire operation

of UTDMS. On the power on, the

microcontroller detects the presence of

stepper motor controller and then polls all

the keys, located on the system front panel.

The front panel has in all eight switches

for- +JOG1, STOP1, -JOG1 for Z-axis and

+JOG2, STOP2 and –JOG2 for Theta axis,

in order to position the transducer for

gauging and two keys for initiation of the

B-Scan and C-Scan image acquisition

modes. Pressing `B-scan’ push button

switch, the B-Scan mode of acquisition is

initiated. The data acquisition is always

performed in synchronization with the

movement of the transducer. The B-scan

image data can be acquired either

advancing the transducer in linear (Z) or in

rotary (Theta) direction. The `C-scan’

mode is initiated by pressing relevant push

button switch and the UTDMS moves the

transducers in a sequence of Z and Theta

axis increments in order to cover the user

specific region of the tube. When the

transducers are stationary, the data for wall

thickness and water path is acquired and

transmitted to COM3 of PC, for data storage.

The COM4 port of PC is utilized for post

acquisition analysis i.e. for bringing the

transducer back to the required location, for

confirmation of located defects in B and C-

Scan mode of acquisition. This feature is

called as ‘Return-On-Defect’ mode.

4.2 Ultrasonic Spike Pulser and Receiver

Boards

To achieve a high axial resolution, use of

high frequency and highly damped

transducers is imperative. To energise such

transducers, a spike pulse is suitable. As the

tubes under inspection have smaller wall

thicknesses (1-10 mm), a suitable wideband

Ultrasonic Spike Pulser and Receiver (UPR)

board has been developed. The UPR consists

of – 1) Trigger Section; 2) High Voltage

Spike Pulse Generator; 3) Limiting network

and Wideband Amplifier. For precise

measurement of WT, ID and OD of the tube,

two ultrasonic immersion transducers are

used and they are placed 180o apart. Instead

of multiplexers, two independent channels of

ultrasonic Pulser Receivers are employed for

excitation of these transducers.

4.3 High Speed Synchronous Counter Boards

The high-speed counter boards have been

developed to perform simultaneous precision

counting of WT & WP for two channels. The

functions of a counter board are broadly

classified into Digital Control Section; High-

speed counter section; Analog signal

conditioning and comparator section for

generation of pulses equivalent to WP&WT.

The Digital control section is further divided

into three subsections namely 1) Trigger

synchronization; 2) generation of a pulse,

whose width is equivalent to the water path

and 3) generation of one more pulse, whose

width is equivalent to the wall thickness of

the tube. The received RF echo signal has

three components viz. i) Initial ringing of the

transducer corresponding to transmit pulse, ii)

An interface echo corresponding to ID of the


NDE-2006 225

tube and iii) The phase inverted RF Echo

signal corresponding to the back surface of

the tube (i.e. reflection from OD), as

shown in the Fig. 1. Using a transmit

trigger signal and the ID-echo signal, the

‘ID-pulse’ is generated whose width is

equivalent to the water path. The water

path is computed using a 10 MHz clock,

derived from the on board 100 MHz clock.

The 8 bits, high-speed counter measures

the water path delay precisely, with a

resolution of 100nsec. An ‘OD-pulse’,

whose width is equivalent to the wall

thickness, is generated using the ID-echo

signal and OD-echo signal. The wall

thickness is measured with a precision of

10nsec, by using 100 MHz clock and 8

Bits counter. Both the counters for WP and

WT are interfaced to the microcontroller in

memory mapped I/O manner. The count

values corresponding to WP and WT of

each channel are transmitted to PC for

storage purpose. The WP and WT values

along with the known separation between

the transducers are utilized to precisely

compute ID, OD and WT of the tube at

any location.

4.4 RS232 to RS485 Converter Module

The 89C51RD2 microcontroller has a

RS232 port for serial communication. The

data and commands are transmitted /

received between the two axes stepper

motor controllers and the host PC. To

translate the single ended RS232 signal of

the microcontroller into a differential

RS485 signal (for better noise immunity

over large distance), a commercially

available converter module has been used.

4.5 Host Computer with Two RS485 Ports

The microcontroller transmits the WT

and WP data to the COM3 port of the host

- Industrial PC along with suitable header,

in order to distinguish data from

commands. Scanner movement can either

be controlled by UTDMS or through the

COM4 port of the host PC. COM4 of the

PC is used to activate ‘Return on Defect’

mode, which provides confirmation of any

anomaly found during the gauging of a tube.

This feature can be invoked during the

retrieval of B and C-Scan images.

4.6 2-Axes Mechanical Scanner, Transducers

and Water Tanks and Pump Assembly

Suitable for Tube Inspection from ID Side by

Immersion Mode

A specialized Z-Theta mechanical scanner

has been designed exclusively for this work

and it has been used for ultrasonic imaging as

well as for gauging of tubes. The scanner is

capable of inspecting tubes and pipes from ID

side, under immersion mode. The multi-

channel approach for inspection and gauging

of tube, results in fetching substantial saving

of inspection time. In essence, the Z-Theta

mechanical scanner developed for tube

inspection from ID side enables to carry out:

(1) Volumetric inspection (i.e. flaw detection)

of tubes with the help of ULTIMA 100M8

and (2) On-line gauging (i.e. dimension

measurement) of tubes with the help of

UTDMS.

5. Experimental Results

For the evaluation of the ULTIMA 100M8

and UTDMS, sample tubes of Zircaloy and

Stainless Steel (SS) have been fabricated.

Inspection results are as follows:

The sample tube made of Zircaloy has

typical dimensions such as: ID = 103.4 +0.4/-

0 mm, OD = 112.7 +/- 0.3 mm and WT = 4.3

+/- 0.4 mm. On this tube, artificial defects in

the form of a groove and a Flat Bottom Hole

(FBH) are machined on the outer surface. The

groove is 2.75mm deep and 10 mm wide and

the hole is 2.75 mm deep and 4 mm in

diameter. The B-scan image data of a tube

covering these two defects has been acquired

using UTDMS. A B-Scan image of the same

zone of the tube has been acquired using

ULTIMA 100M8 system. The results are

shown in Fig. 5. It has been observed from

the Fig. 5 that, the results acquired using

Ultrasonic Imaging technique and Gauging

method matched very close with an accuracy


NDE-2006 226

of +/- 100 microns. The B-Scan image

acquired by ULTIMA 100M8 has

provided information regarding the

interiors of the tube along the wall-

thickness and about the orientation of

these defects. The gauging results also

provide a profile of ID, OD, and WT of the

tube under testing, over the same length.

[The groove is not machined, exactly

perpendicular, to the tube length and the

effect can be seen in the B-Scan images,

acquired using ultrasonic imaging system

and also in the form of an offset in the B-

Scan images acquired by UTDMS.]

The sample tube of SS has dimensions:

ID = 103.6mm, OD = 112.7mm and WT =

4.5mm. Two grooves have been machined

on the OD, as artificial defects. The first

groove has a depth of 1mm and a width of

20mm; the second groove is 10 mm away

from the first groove with 2mm depth and

15mm width. Experiments similar to

section 5.1 have been carried out by

acquiring the B-scan images using a

gauging and an ultrasonic imaging

technique.

The WT, ID and OD values for

Zircaloy tubes have been confirmed by the

digital vernier caliper with 10 microns

accuracy and the results derived from

inspection and gauging technique have

been found within 50 microns accuracy for

WT and within 100 microns accuracy for

ID and OD.

6. Discussion

The ultrasonic tube dimension

measurement system UTDMS has been

tested for gauging of various samples of

metallic tubes and the results have been

supplemented by the cross-sectional B-

Scan images acquired using a multichannel

ultrasonic imaging system ULTIMA

100M8. For the UTDMS, the wall

thickness measurement has a precision of

10 nanoseconds, which is equivalent to 24

microns in Zircaloy. (Noting that, the

acoustic velocity of Zircaloy is 4800m/s).

The water path is measured with a precision

of 100 nsec., which is equivalent to 75

microns in water, considering the acoustic

velocity of water as 1500m/s. In conclusion,

the UTDMS provides highly precise and

accurate measurements of dimensions for

metallic tubes/pipes. The total system is

extremely useful for establishing the

procedures for inspection and gauging of

metallic tubes and pipes. Tubes/Pipes of

longer length can be tested by using a

modified scanner capable of handling such

tubes, with a provision to compensate for

temperature variation.

7. Acknowledgements

Authors are extremely grateful to Shri.

M.D. Ghodgaonkar, Head, Electronics

Division, BARC, Dr. S.K.Kataria, Ex-

Associate Director (E), E&I Group, BARC

and Dr. Mrs. Dixit, Ex-Director, VJTI,

Mumbai for their encouragement and support

for this work. Authors wish to express their

thanks to Shri. S.P. Srivastava of CDM,

BARC for his valuable guidance in the

mechanical design of the scanner. Very useful

suggestions made by Shri. P.P. Nanekar and

Shri. M.D. Mangasulikar of AFD, BARC

regarding the procedures for ultrasonic NDT

of tubes, are also gratefully acknowledged.

Authors are also thankful to Mrs. Shewta

Rane, Mrs. P. Jyothi and Shri. L.V.

Muralikrishna of Electronics Division, BARC

for their technical assistance in the fabrication

and testing of system hardware and making

useful phantoms for system

calibration/checking.

8. References

1. Non Destructive Testing Hand Book, second

edition, Volume 7 – Ultrasonic Testing,

American Society for Non Destructive

Testing, 1991, ISBN-0-931403-04-09.

2. Kazys R., Mazeika L. et al. from Kaunas

University of Technology, Lithuania “

Ultrasonic Measurement of Zirconium Tubes

used in Channel Type Nuclear Reactors”,

NDT&E International, Vol. 29, No. 1, pp. 37-

49, Feb. 1996.


NDE-2006 227

3. Patankar V.H., Agashe A.A., P. Jyothi,

Joshi V.M. “ ULTIMA 100M8 –

Multichannel Ultrasonic Imaging System

for NDE of Tubes/Pipes ”, Xth

National

Conference On Ultrasonics, Osmania

University, Hyderabad, India, March 15-

16, 2001.

4. Patankar V.H., Joshi V.M., Srivastava S.P.

“Development of a 4-Channel Ultrasonic

Imaging System for Volumetric Inspection

of Solid Cylindrical Forgings”, Journal

For Non Destructive Evaluation (JNDE)

Vol.2, Issue 3, pp 35-40, December, 2003.

5. Anish Kumar, Rajkumar K.V., Palanichamy

P.P., Jayakumar T., Patankar V.H., Joshi

V.M., Lande B.K., Chellapandian R.,

Kasiviswanathan K.V., Baldev Raj

“Development and Applications of C-Scan

Ultrasonic Facility”, Journal For Non

Destructive Evaluation (JNDE) Vol.4, Issue

1, pp 11-16, June, 2005.

6. Ph.D. Thesis of Patankar V.H., University of Mumbai, 2006.

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