Centrifugal Absorption Recip/Screw/Other
Eddy Current Testing
Contractor Requirements

                                         “Quality First”

In trying to maintain our “Quality First” image, Eddy Current USA Inc would like to point out the different techniques and qualifications we believe make us the best Heat Exchanger Eddy Current Testing Company available.

All   E-Tech Services “On Site Data Analysis” Technicians are Certified to:
* ASNT Level III                      * Minimum 5 Years Testing  Experience
* Zetec Level IIA (Nuclear)      * National Chiller Manufacturers Test
  * All Reports are reviewed by an Eddy Current Certified ASNT Level III

All Eddy Current Tests are Dual Frequency (Display); Four Frequencies Tests utilizing ZETEC MIZ-40A Test Equipment. Including:

Dual Frequency X-Axis Test – Unique in determining the Size of Defects and geometric changes such as Expansions, Over-Expansions, Mis-Expansions (Freeze) Bulges, Dents, Circumferential Cracks, Gradual Large Volume Indications, Metal Loss Inside Diameter or Outside Diameter.

Frequency One is used as the Baseline Test and is displayed on the Video Screen for visual analysis.  It is calibrated to show the difference between Geometric changes (Expansions, Bulges) and Conductivity Changes (Metal Loss, Gain).  Support Damage is calibrated at (.005) Five Thousandth’s of an Inch/ 180 Degree around the circumference of the tube = 1 Div./ Deflection on the Video Screen

Frequency Three is used as a Higher Frequency, Higher Magnification “Confirmation” Channel and is not displayed on the Video Screen unless confirmation of a Small volume indication on the X-Axis Test is required.  You know when I change to High-Mag, I'm lookn for those Micro level indications.

Dual Frequency Differential Test – Unique in determining the Depth of Defects such as Small Volume ID or OD Pits, Cracks, Inclusions, Pin Holes, Fatigue Cracks, Stress Corrosion Cracks.

Frequency Two is used as the Baseline Test and is displayed on the Video Screen for visual analysis.  It is calibrated to ASME Specification for Testing Non-Ferromagnetic Tubes in High Pressure Heat Exchangers.  The 1/16” Through wall Hole is calibrated to show 4 Div./Deflection (1/2 of the Video Screen) response.  This test is very accurate at determining the Location (Inside or Outside Diameter) and DEPTH of the Indication as a Per Cent of Tube Wall

Frequency Four is used as a Higher Frequency, “Confirmation” Channel and is not displayed on the Video Screen unless confirmation of a large volume indication on the Differential Test is required or a High Frequency High Gain Micro level indication is confirmed. 

While many testing companies offer either or both tests separately,
Eddy Current USA Inc performs ALL Tests simultaneously

Eddy Current USA Inc Eddy Current Tests are Recorded on DVD for:
* Inspection Integrity                            * Customer Confidence
* Permanent Record                             * Inspection Repeatability

Other, and there are few, testing companies that make a permanent record of the test inspection, Eddy Current USA Inc takes a VIDEO PICTURE of the Complete Test as it is being performed, showing the computer screen at all times.  This includes Two Display Tests X-Y Mode (One X-Axis and One Differential), Two Strip Chart Recordings Usually Horizontal X-Axis and Vertical Differential, DVD also includes an audio channel that lists the Row # and Tube #, along with any additional commentary about the indications presented on the Video Screen.  This Disk is an actual “Real Time” Video copy of the test as performed by the technician at the time of the test.
Computer Generated Eddy-Current Test Report Including:
* Cover Page (Chiller Location, Model #, Serial #, Test Date, Customer Location)
* Table of Contents
* Calibration Information of Test Equipment (Frequency, Gain, Phase, Probe etc.)
* Heat Exchanger Information (Tube Type, Size, Test End, Support Distances etc)
* Test DATA including all reportable Indications.
* COLOR Coded Tube Sheet Diagram of Heat Exchanger
* Report Summary including Relevant and Non-Relevant Indications, Tube Totals, Tube Indication Percentages, Eddy Current USA Inc “Considerations” and “Recommendations”

Sample Reports are available upon Request.

Competitive pricing without sacrificing “Quality”.  Our primary goal at Eddy Current USA Inc is to provide and perform the most comprehensive, technologically advanced “Heat Exchanger” Eddy-Current Test tube analysis and report for the least expensive price.

“Eddy Current Outline”

Eddy Current Testing is a Non-Destructive Test performed on Non-Ferromagnetic Tubes (Non Magnetic) installed in Commercial Heat Exchangers, such as those used in Commercial Chillers (Absorption, Centrifugal, and Reciprocating), Condensers and Feed-water Heaters in Power Plants, Stainless Steel Exchangers used in Petrochemical, and Pharmaceutical and Materials Processing facilities.  Used to locate and identify any Abnormalities that may lead to Premature Failure of the Tube (s) in Service.

One of the First Non-Destructive A/C Field Tests was performed by Thomas Edison on President Garfield when he was hit with an assassin’s bullet.  Sorry to say the result was not positive.  Glad to say technology has developed this test dramatically.  Many of the Modern Theories and Practices used today were developed in the 1940’s by a German Scientist by the name of Dr. Foerster.

Modern ID Tube inspection was developed in the United States by Zetec, around 1957 primarily for use to test tubes located in steam generators on Nuclear Submarines of the United States Navy.

As you can see, Eddy-Current Testing is a relatively New Test.  The last ten years of technological breakthroughs in Micro-Electronics and Computers have propelled this test from a “Black Magic” type test to a fully documented, very reliable Non-Destructive test used in virtually all aspects of Manufacturing and Service.  I have 25 Years of Eddy Current testing Experience in the Chiller Industry, This translates into over 2,000 different chillers tested Nationwide over the years.


Essentially, an eddy current test can be closely linked to transformer theories.  A basic fundamental of a transformer is that any change in the secondary (Coil) is reflected as an Impedance (Load) change in the Primary (Coil).  In eddy current testing the Primary Field is the Probe that is inserted in the tube.  The Secondary Field is the Eddy Current Field induced in the Tube.  Any change in the Eddy Current Field is reflected as a load change in the Probe.  The Eddy Currents are flowing at right angles to the Induced Electromagnetic Field.  (A good rule of thumb is that the Eddy Currents are flowing in the Direction that the Originating Field Coil Wires are wound).  The Technician than inserts the probe into the tube, and push’s it to the far end and out of the tube.  It is than Pulled Back, While this is done the technician “Views” the Video Display and watches the screen for signal changes.  The size (Amplitude) and angle (Phase) of the signal changes allow the technician to “Identify” the change as a relevant or non-relevant indication.  These signal changes are “Compared” (Differentiation) to signal changes generated by defects from a “Known Standard”.

Affecting Influences:  (Load Changes)

1)      Permeability - is the most influencing factor, it is the ability of a material to be magnetized.  Iron, Steel etc.

2)      Conductivity – The ability to conduct electrons, conductivity is the factor most associated with Defect Discontinuities.  Heat Treat, Work Hardening, Corrosion, Erosion, are examples of gradual conductivity effects.  Pits, Cracks, Support Damage are examples of localized conductivity effects.

3)      Geometry – The distance of the Originating Field (Probe) from the Test Surface.  Also called Lift Off. Examples of Geometric effects are Land Areas, Internal Expansions, Freeze Bulges.

Only these three factors can affect the Eddy Currents flowing in the tube.  Since our probe is located inside the tube, and the eddy current field is generated from inside to outside, Permeability factors such as supports and baffles do not significantly affect our test.  So essentially we are monitoring TWO factors.  Conductivity and Geometry.


1)         Signal Generator:  Supplies a Sine wave at a selectable frequency to a Coil.  This generated an electromagnetic field.  (Primary Field)

2)         Bridge Circuit. When this Electro-magnet is placed in the vicinity of a Non-Ferromagnetic material an Eddy-Current is developed in the material.  This Loads the Coil and Unbalances the Bridge.

3)         Balance Circuit – Adjusts the unbalanced bridge to balance.  Puts the Loaded Coil output to 0.

4)         Amplifier – amplifies the output of the bridge to a usable signal amplitude.

5)         Display – used to measure the output signal, can be a meter, buzzer, light, CRT, or Computer Screen.

Probes and Test Procedures:

1)      Absolute Test.  Uses One Coil to Generate the Eddy Current field and Monitor and changes in the Eddy-Current Field.  This test is very useful in locating and identifying most Indications.  It has Good Geometry vs. Conductivity Resolution.  It gives a TOTAL value change of Geometry or Conductivity.  it is very accurate at Identifying Gradual type indications.  It is Not Too accurate at determining the Depth of a discontinuity, only the Total Size of a discontinuity.

2)      Differential Test.  Uses Two coils Opposing, to Generate the Eddy Current field and Monitor changes in the Eddy-Current field.  This test is very accurate at determining the DEPTH of a localized discontinuity, Pits, Cracks, etc.  Listed as a Per Cent of Wall.  This test is not very accurate at determining gradual effects.

Eddy Current USA Inc utilizes both tests simultaneously (2) Absolute (in our case we use a X-Axis Coil Configuration) tests and (2) Differential Tests.  Each test gives a unique “Picture” of the Indication, for analysis.