AUTORS : Ing. Václav Svoboda , Ing. František Žemlička, Preditest s.r.o.

Practical application of Magnetic Memory Method and comparison with Acoustic Emission and Ultrasonic Method

11th European C

onference on Non-D

estructive Testing (E

CN

DT

2014), October 6-10, 2014, Prague, C

zech Republic

Inspection of water chamber tubes of boiler by MMM

First part – inspection of water tubes of boiler chamber

Hp-3

dH3/dx

Hp-4

dH4/dx

Hp-5

dH5/dx

Hp-6

dH6/dx

Hp-7

dH7/dx

Hp-8

dH8/dx

trubka c.1. cista file 13

Lx,mm

460440420400380360340320300280260240220200180160140120100806040200

460440420400380360340320300280260240220200180160140120100806040200

H,A/m

-350

-400

-450

-500

-550

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-1000

-1050

-1100

dH/dx,(A/m)/mm

145

140

135

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115

110

105

100

95

90

85

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

0

Hp-3

dH3/dx

Hp-4

dH4/dx

Hp-5

dH5/dx

Hp-6

dH6/dx

Hp-7

dH7/dx

Hp-8

dH8/dx

trubka c.2. cista misto vady (dira) file 16

Lx,mm

420400380360340320300280260240220200180160140120100806040200

420400380360340320300280260240220200180160140120100806040200

H,A/m

-640

-660

-680

-700

-720

-740

-760

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dH/dx,(A/m)/mm

50

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40

38

36

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0

Ultrasonic testing of both tubes

Lacation of defect in tube 1

Lacation of defect in tube 1- Another position

Ultrasonic inspection of Tube2- No defects were found

Conclusion

- Tube 1 was in the service for a long time (over 20 000 hours)

- Tube 2 was not in the service

- It is possible to check by MMM water tubes in the boiler chamber

Second part – Comparison of MMM with AE inspection on the gas pipeline DN 500 containing defects

Abstract :

The contribution is devoted to the diagnosis of technical facilities and structures based on the material's magnetic memory in combination with the acoustic emission method.

Some examples of successful application of this approach to an experimental segment of a welded pipeline DN 500 with various types of defects are presented. Both of the methods of diagnosis were used within the planned experiment.

The test pipe was subjected to pressure cycles in specific stages with simultaneous measurement of acoustic emission. The results of measurement indicate a very good agreement between the two methods as regards both localization of the defects and evaluation of their severity.

The method of magnetic memory of the material

was applied by using a TSC-3M-12 measuring system

enabling stress concentration zones (SCZs) to be recorded

and localized in combination with a Type-11 probe, designed

for contactless diagnosis of buried pipes.

This measuring system records the signals by

means of probes either in the time domain or in

combination with a wheel for measuring the length run.

Signals were recorded along the pipe length every 4 mm,

guaranteeing a sufficient sensitivity of measurement at each

site of the material.

2.1 - Application of the method of the material's magnetic memory

Fig. 2.1.1 - Magnetic Memory Method - Contactless measurement

This method was repeatedly used prior to starting the pressure experiments with a view to identifying the initial SCZs associated with the existing defects in the piping.

Fig. 2.1.2 – Contact measurement

2.2 - Application of the acoustic emission method

A total of 26 acoustic emission sensors weremounted along the whole pipe at a constant spacing(Fig. 2:2). This number and distribution of the acousticemission sensors guaranteed optimum sensitivity ofmeasurement, including linear localization of anyemission sources in accordance with ČSN EN 14584.

An ACES IDT 04 multi-channel (40 channels)acoustic emission measuring system in combination withmeasuring probes and a control computer was used forrecording the emission signals. The measurement wascontinuous, controlled by special software.

When measuring in the linear localizationmode, the sequence of the emission signal arrivals tothe probes included in the measuring network wasrecorded, including the delta – T – times, and the knownemission signal propagation patterns in conjunction withthe known geometry of the pipe served as the basis forreal-time localization of the signal source.

Fig. 2.2.1 – Instalation of AE sensors

A total of 12 emission sources, mirroring the emission activity of the defects in the pipe in the initial state, were localized during this cycle.

Fig. 4.1 and 4.2 illustrates a comparison between the results of emission source localization and the results of inspection by the contactless method of the material's magnetic memory – determination of the stress concentration zones.

Comparison of the two graphs gives evidence of a very good agreement between the

results of the two non-destructive testing methods.

Fig. 4.1

Fig. 4.2

Pipeline DN 500

Fig. 4.4 – Three pressure cycles and AE activity

5. Conclusions

The following conclusions can be drawn from the results of the material magnetic memory

method and the acoustic emission method using a test pipe DN 500 with defects and

applying 3 pressure cycles:

1. The material's magnetic memory (MMM) method is well suited to contactless

diagnosis of buried pipelines, with the aim to rapidly detect the stress concentration zones,

where material degradation processes occur preferentially.

2. The acoustic emission (AE) method is well suited to the diagnosis of pipes which

are subject to stress changes due variations in the internal pressure, i.e. pressure

increase/decrease cycles.

3. The acoustic emission method can be used for both linear and planar localization

of emission sources which may be caused by existing or emerging defects in the pipe

material.

4. Any detected defects of lower emission activity can be blocked by a pressure

cycle which exceeds the operational pressure level.

Metal Magnetic Memory Method – Another application

on storage tank

Metal Magnetic Memory Method – Another application

on storage tank

How to improve credibility as a result of applied various NDT metod

Third part:

1. Application of various NDT methods depends on possibilities of its physical principles

2. Every NDT method has its scope of use and also some limitations

3. Mutual combination of various NDT methods is possible to significantly increase level of inspection in relation to the credibility of results

Example of inspection of spherical tank

Example of inspection of spherical tank

By Acoustic Emission

Schematic view of AE sensors placed on outer surface of the tank

Periodical inspection of welds on spherical tanks is prescribed by procedure.Every 9 years, the welds are inspected by a) Ultrasonic inspectionb) X-Ray inspection

Both inspection made on spherical tank confirmed some defects, which exceed allowed limits. It was decided to apply additionally a) Acoustic emission techniqueb) Magnetic Memory Method

Application of AE during hydrotest prooved no active AE sources in areas where defects were localized by previous UT and X-Ray inspection.Areas of welds with defects were inspected additionally by MMM Method.

And the results are shown on following pictures.

General Conclusion

1) MMM method is possible to use in various areas of industry to inspect

complicated structures

2) Good agreement in combination with additional NDT methods

3) MMM method investigates initial damage of structures caused by service

conditions

4) Its application is relatively quick procedure

5) It can be used also for continuous monitoring of high stressed areas

Thank you for your attention.