CHAPTER
11 A Basic Corrosion Survey
I
n this chapter, we will look at some of the tools and procedures we use to conduct a
basic underwater metal corrosion survey. These procedures typically fall into a special-
ized subcategory in the marine service world, that of a corrosion specialist. (In fact, one
of the certifications that the ABYC offers is for corrosion. Interestingly enough, the ABYC
also strongly recommends that those who sit for this certification have the ABYC Electri-
cal Certification as a prerequisite.) Underwater metal corrosion can be caused by failures
or improper installations of electrical systems, however, so general marine electricians and
dedicated do-it-yourself boatowners should at least be aware of the basics of the subject.
Those who wish to delve further should contact the ABYC’s Education Department and
register for a Corrosion Certification course and exam.
My goal in this chapter is to provide you with enough knowledge to perform a
basic corrosion survey, which will include looking for stray DC current caused either
by faulty wiring or defective DC appliances. I will also cover the galvanic isolator
and how to determine if it is in good working order. Since a galvanic isolator may be
an integral part of the boat’s AC grounding system, its proper functioning is critical
to crew safety.Tools of the Trade
The corrosion specialist uses a variety of arcane equipment, special reference electrodes,
conductivity testers, water pH and salinity testers, split-out shore cords, prewired galvanic
isolators, extra anodes of different materials, and an absolute plethora of gear to do his or
her work.
However, for the marine technician and advanced boatowner, I’m going to focus on
two specific tools: a silver/silver chloride reference electrode and an extremely high resolu-
tion DC amp clamp, such as the one shown in the photo on page 117. In addition, you
will need your standard DVOM.
A special electrode is necessary because (1) we will be measuring extremely small volt-
age potentials; (2) we will need extremely high levels of sensitivity and precision; and (3)
we must be able to repeat the test in a variety of electrolytes (i.e., water of various degrees
of salinity). The silver/silver chloride electrode meets all these requirements; it is the most
common reference electrode used in marine applications due to its ease of manufacture
and its stability over a wide range of temperatures.Copyright © 2007 by Edwin R. Sherman. Click here for terms of use.