EMAT

INTRODUCTION

Pipe Section

This section provides information on the application of EMAT Technology used to detect corrosion in pipe systems. The technique detects but does not discriminate between corrosion on either surface of the pipe. This technique provides qualitative not quantitative information on the severity of the corrosion.

THEORY OF EMAT TECHNOLOGY:

Inspection Instrumentation

The EMAT is an ultrasonic transducer, which operates without the application of liquid couplant. The EMAT transducer generates the ultrasound in the material being tested. As with piezo-electric transducers, different modes of ultrasound can be generated in the material to be tested by varying the design of the EMAT transducer. The robot has two EMAT transducers mounted such that the transducers are closer than a diameter apart. The transducers introduce sound to the material; the sound is transmitted circumferentially in both directions. A further advantage of this type of transducer is that it can be designed to operate at elevated temperatures. The application discussed in this document uses a lamb wave mode of ultrasound.

THE EQUIPMENT

EMAT Scanner

The equipment is normally housed in a trailer, which is located within a few hundred feet from the test location. The instrumentation consists of a pulser receiver unit with a Computer to monitor the inspection. The test signal is displayed on a computer monitor. The output signals can be printed in color for insertion in the field report.

THE CALIBRATION

An umbilical cable connects the instrumentation to the test vehicle, which is used to scan the test area. Once the equipment is connected, the transducers have to be calibrated on a representative sample of pipe.

THE INSPECTION

The inspection can be performed on horizontal or vertical runs of pipe and is used to detect areas of localized corrosion. The equipment records data from various signal frequency modes. An analogue output is supplied that provides a record of the condition of the pipe or pipe support. By applying this technology to pipe systems, we can perform a fast global inspection of the circumference of the pipe. By monitoring the time of flight of the sound, the operator can differentiate between the area immediately between the probes to inspect areas associated with pipe supports and the remaining area on the upper region of the pipe.

Ultrasonic Data

The application of the EMAT technology allows large linear sections of pipes to be scanned for corrosion. The system is also used successfully for the inspection of pipe supports and corrosion associated with the pipe supports.

Pipe Support Corrosion

Scanner on Dock Line

EMAT magnets

Permanent EMAT magnets can be used for the inspection of stainless steel pipe. This example shows EMAT successfully collecting data from a calibration standard and identifying areas simulating isolated pitting and corrosion with great clarity.

ADVANCEMENT IN EMAT TECHNOLOGY

The latest upgrades to the EMAT system bring technology advanced electro-magnetic control provides a closely defined ultrasonic pulse while noise canceling receiver design improves signal to noise ratio. In combination, these advances provide the ability to obtain greater discrimination in inspected data. Improved electronic provide higher data acquisition speeds as well as improved precision. As an example the detection of corrosion in pipe support areas, hidden behind stitch welds, can now be identified with great clarity; previously the indication were difficult to separate from noise.

EMAT technology

With this higher quality data, analysis, using both amplitude and time -of -flight information, provides a clearer picture of the condition in the collected data.

Repeatability of data from sequential inspections is improved which, in conjunction with calibration standards, improves confidence in the data collected.

Test Sample 2

Test Sample 1

EMAT technology