article first appeared in the 1983 inaugural issue of Corrosion
Control magazine, Kay Publishing.
The science has grown since then, so don't take issue with the
technique as outlined, this is just a writing sample, not a
current technical article.
good testing system - if operator skilled
One of the most effective
and cost efficient methods of testing heat exchanger tubing systems
is the Eddy Current method, but users must be sure the people doing
the testing know what they're doing.
Industry sources say that
increasingly, companies hoping to cash in on the use of the method
are fielding teams of ill-trained testing people who can't really
interpret the results they receive from the instrumentation.
That means a lot of money
is being wasted on such testing and in many cases damaging corrosion
is going undetected.
The Eddy-Current method
has been widely recognized throughout North America as one of the
best non-destructive systems developed to date for applications
such as commercial heating, ventilation and air conditioning (HVAC)
Testing is accomplished
by passing a four inch probe, attached to a flexible tube housing
wires, through the entire length of a tubing system, or into bundles
of tubing, to locate faults such as pitting, cracking, wear and
The probe holds four coils.
Two emit Eddy-current fields which measure smaller defects within
the tubing and the other two measure large defects, and both sets
display them on a cathode ray screen.
It is then up to the technician
to interpret the information provided by the scope. If he can't,
the testing is worse than useless, because the end user is out the
cost of having his unit tested, and may still end up with system
damage. And in a $150,000 system, it's not uncommon to spend $50,000
for repairs when leakage occurs.
The cost of testing varies
from add up, in some cases, to $1,600 for an entire system. If,
for example, the client does have a faulty tube in his system, the
Eddy-Current method will detect and locate the problem.
The cost of replacing a
tube might run to $100, but if the fault is not repaired and water
eventually leaks into the system, the damage can, conceivably, amount
to the cost of a whole new system.
It's not too difficult to
see the advantages of regular testing with this method. It's also
easy to understand why the person doing the testing must be a fully-trained,
highly qualified technician able to read the results accurately.
Hunter Blakely & Associates
of Charlotte, North Carolina, one of the pioneers in developing
the Eddy-Current method specifically for air conditioning units,
have a training course for their technicians which lasts a year
or more. The course adheres to the guidelines set down by the American
Society for Non-Destructive Testing. Only on completion of the course
is a technician sanctioned for testing.
As Hunter Blakely says,
"An Eddy-Current instrument has considerable potential if used in
proper hands. There are a very large number of people out there
who have purchased instruments and set themselves up in the testing
business, but there is also very little attention paid to the training
Some manufacturers offer
short training programs to purchasers in the use of the instrument,
after which the buyer is given a certificate stating he is a testing
technician. Blakely is opposed to this practice, as are Canadian
service companies like D'Arcy Sweeney Ltd.
Mike Lambert of DSL told
us. "A little training is better than none, but people who buy these
instruments and set themselves up in business without proper training
It would be like me buying
an electrocardiogram machine and testing patients for heart disease.
You just don't do that. This is an art as well as a science and
it takes time and thorough training to become competent."
In Canada, so far, there
is no regulatory body or sanctioning group involved with systems
testing using the Eddy-Current method. Although there haven't been
the numbers of unqualified personnel in the field that plague the
American market, the few who are out there doing improper testing
are casting a pall over the credibility of reputable service companies.
The end user receiving erroneous results from the method doesn't
always differentiate between the method and the testing technician.
The problem is compounded
in the United States, and to some extent in Canada, because many
insurance companies are beginning to insist that system owners and
maintenance managers have their units tested regularly. A commercial
air conditioning unit should be tested every three years until a
fault is located, then each year thereafter until the fault is corrected.
Then the testing should resume on a three year basis, says Lambert.
One method suggested is
to set out testing guidelines relevant to the training and qualifications
of the field personnel, as the American Society for Non-Destructive
The best advice Lambert
and Blakely offer to owners and managers of HVAC systems is to "screen
companies thoroughly before any testing begins."