Salt chlorine generators often are accused of corrosion, but what is the real culprit?
There has been much mis- and dis-information spread on the subject of salt chlorine generators’ role in corrosion, while very scant, solid data is presented.
In 1982, D.S. Novak, an employee of salt chlorine maker Eltech Systems Corp., wrote a report based on a study by Professor Robert F. Hehemann, PH.D. of Case Western Reserve University’s Dept. of Metallurgy and Materials Science. It focused on the three following factors that were believed to contribute to corrosion: 1. Chlorine Levels 2. Cyanuric Acid 3.
The findings were a surprise because they showed that high chlorine levels were the primary cause of corrosion — not salt as is the common misconception. In fact, a corrosion-induced leak could occur in grade-304 stainless steel within eight days of being exposed to 20 parts per million chlorine, with no cyanuric acid present.
A small amount of cyanuric acid, 10 to 20 ppm, can actually slow down corrosion. Salt levels of up to 3,000 ppm have a relatively insignificant effect on corrosion.
As a provider of commercial chlorine generators, I have come across this a number of times. Here is my experience with corrosion. But first let me tell you about two incidents I have come across in the field.
I was contacted by a frantic owner of a dive pool who had just had his pool completed and was starting it up: “We can see corrosion coming out of the jets, and the pool builder told me it was the salt, and you have to come down and fix it!”
“Where is the salt?” I asked him.
“In bags on a pallet by the side of the pool!” he replied.
The second very interesting incident happened when we were on-site for the start-up of a large, three-pool complex and noticed that none of the equipment had been bonded. We tracked the electrician down and brought this to his attention. His response: “Bonding is not in my scope of work.”
Corrosion — Above the water Chloramines can cause corrosion on all metal parts within a pool enclosure, such as light fixtures and steel kick plates on doors. And in extreme cases, indoor facilities can collapse as corrosion eats away at the steel support structures. We’ve seen this happen in Switzerland in the 1980s, and there have been many similar incidents since. This is not caused by the salt from the salt systems, as it will not evaporate from the pool.
Rather, much the same as chlorine, salt can be splashed out of the water. To prevent corrosion, periodic rinses with fresh water, as should be done with a traditionally chlorinated pool.
Corrosion — In and within the water and pool equipment This is where the finger of guilt has been firmly pointed at salt, and it is just not correct. I have seen corrosion in many a non-salt pool, and the cause of the corrosion is the same for traditional chlorine pools, especially those treated with liquid chlorine.
So what is going on here?
Well, quite simply, it is an issue of lack of and/or improper bonding of metallic pool equipment.
The National Electrical Code requires bonding as part of its Rule 680.26, but it seems that many professionals do not know the difference between grounding and bonding. And while they take great care to ground all electrical equipment, bonding is, in many instances, ignored.
Bonding lugs are provided on all mechanical equipment in pump rooms for a reason. If the bonding is not correctly installed, or not tied into an equipotential bonding loop, and not terminated correctly, then the addition of salt into the water creates a battery-like situation. The conductive ions, or salt particles, then provide a path for the current flow, MVDC, to ground itself to a metal pool component, beginning the corrosion process.
It is important that the pools’ rebar, and all metallic railings, ladders and, of course, the pumps, filters (if metallic) and heaters, and even the HVAC system, be bonded into this loop. A salt system will introduce around 3,500 ppm of salt into the water in a very short period of time, so the corrosion from improper bonding will be quickly apparent.
In contrast, if liquid chlorine is the sanitizer of choice, then for every gallon of chlorine added, approximately 2 to 3 pounds of salt is formed, raising the salt level in the water, sometimes getting to levels that can be comparable to that of a salt pool.
I raise this issue because what we have here is a global concern of bonding and how we, as an industry, can provide the correct solutions for our clients, rather than resort to finger pointing.
Pool builders need to ensure that their electrical subcontractors are aware of this requirement. The construction punch list should include steps for all bonding locations to verify that they are in compliance. It is not enough to assume that the electrical inspector will be responsible for catching missed and broken bonds.
Source: Pool and Spa News