Corrosion Technical Topics
Thanks to the Online
For corrosion stuff, contact me through my employer, Corrpro in San Diego.
Definitions by NACE International
Stray Current: Current through paths other than the intended circuit.
Electrical Interference: Any electrical disturbance on a metallic structure in contact with an electrolyte caused by stray current(s).
Taken together we get Stray Current Interference.
Disclaimer: This text is adapted from a discussion in on LinkedIn. The information is offered as is, without any guarantee of it accuracy or applicability to a particular situation or facility. The information must not be relied upon for any design or testing or decision making. Testing cathodic protection systems and AC equipment must always be performed by persons trained in electrical safety and other topics.
Corrosion of metal water pipes and other buried facilities can be caused by stray current interference. Susceptible pipe materials: ductile iron pipe (DIP), cast iron pipe (CIP), concrete pipe with steel linings (PCCP) and welded metal pipe.
When the conditions are suitable for stray current interference and mitigation factors are not employed then yes, you can have accelerated corrosion problems. Stray current is also a bugaboo that people point to when they find corrosion. Verification is fairly easily determined by a trained CP expert.
Stray current caused by direct current (DC); cathodic protection (CP) systems and traction power transit systems: Stray on other buried utilities and structures should be considered as a part of the design and operation of CP systems and traction power transit systems. Designs features to minimize the risk of stray current interference include carefully selecting anode bed location, rerouting one or both pipelines, and installing additional CP test stations at strategic and crossing points. For traction power systems, the track-to-earth resistance should be maintained above a set minimum. A typical acceptable uniformly distributed track-to-earth resistance is 500 ohms per 1,000 feet of track (two rails). Additional CP on the buried utilities near the tracks can also reduce the risk of corrosion.
AC induced corrosion: High voltage overhead transmission wires can induce AC voltage onto buried structures and elevated VAC is a risk factor for AC corrosion. Apparently buried AC lines in utility tunnels and ducts are less of a problem. Anyways...
Evaluation and mitigation of AC induced corrosion by high voltage overhead transmission wires requires more specialized design and testing. Many papers and standards on the topic are published by NACE International. Pipeline AC voltage must be kept below 15 VAC to prevent touch shock hazard and sometimes this requires professional technical design and testing. AC induced corrosion phenomenon is strongly correlated with lower soil resistivity along with increased pipeline AC voltage. Papers I have reviewed indicate that AC induced corrosion can occur when conditions are right and the pipe AC potential is below 15 VAC, so....
You asked how common is stray current interference. I think stray current is occurring somewhere on a pipe somewhere at all times.
Disclaimer: This text is adapted
from a discussion in on LinkedIn. The information is offered as is,
without any guarantee of it accuracy or applicability to a particular
situation or facility. The information must not be relied upon for any
design or testing or decision making. Testing cathodic protection
systems and AC equipment must always be performed by persons trained in
electrical safety and other topics.
There was a discussion on LinkedIn where a person found:
After a couple of months in operation the water box polyurethane coating appeared swelled in several points with a loss of adherence between metal substrate and the coating. Bubbles formed up to 100 mm. Water box has several zinc sacrifice anodes."
Zincs are not very powerful (voltage between the steel water box and the zinc anode is only about 300 millivolt), so unless the coating (coating design) is faulty, they will not cause cathodic disbondment.
The more common cause of a coating failure is poor quality control during the coating operation.
I recommended they engage a coating expert holding a valid NACE International Certification: CIP Level 3 - Peer Review to review the records from the coating application project. The review may not require an onsite inspection. The review should include:
the environment, metal substrate, surface preparation, surface cleanliness, dust control methods, temperature control methods, humidity control methods, the coating product data sheet, project specifications, applicator's contractual scope of work, the applicator qualifications, and records of conditions and inspections and tests recording during the coating project. During the project these should have been examined and recorded by the third party, on-site, certified coating inspector.
The review may reveal the cause of the failure before even examining the failure beyond your brief description of the blisters.
I recommend that they do that prior to investigating cathodic disbondment.
I don't believe these devices are effective, and I'm an expert in
corrosion control. Before purchasing an electronic corrosion control sytem for your automobile read what corrosion control experts have published.
Robert Baboian, State of the Art in Automobile Cathodic Protection, Proceedings of the 5th Automotive Corrosion and Prevention Conference, P-250, SAE International, Warrendale, PA, USA, August 1991 (SAE International was formerly called The Society of Automotive Engineers) Paper no. 912270
Robert Baboian, Cathodic Protection of Automobiles-Does it Work?, Materials Performance,Vol 26 no. 7 1987
FEDERAL TRADE COMMISSION (FTC)
In 1996, the FTC fined David McCready and ordered him to pay $200,000 in consumer redress and stop marketing and selling his“Rust Evader”. Dave McCready was also ordered to no longer sell products with warranties with conditions (conditioning warranty coverage or Magnuson Moss Warranty Act, 15 U.S.C. 2302(c),) requiring customers to purchase factory authorized maintenance service before honoring warranty claims. The FTC issued a press release and the final judgment. There were also funds to distribute to the consumers who purchased the purported vehicle anti-corrosion devices.
CAR TALK RADIO PROGRAM
If you don't believe me, consider what the folks at Car Talk on PBS, have to say about this type of product.
As of October 2011, various electronic devices purporting to provide corrosion control for cars are marketed under these trademarked names.
ELECTRO-SHIELD™ PATENTED RUST AND CORROSION INHIBITOR
CounterAct Electronic Rust Protection System Rust Evader® system
Neo Rust Evader
I am disappointed to report that Canadian Tire sells the CounterAct System Product # 47-7905-6
for $299.99 plus installation at an extra cost. The five year
warranty applies only to cars that started out free of rust, is a
shorter warranty term than most auto body warranties and requires
documented annual checkups at the location where the unit was
installed. I bet that Canadian Tire calculates that they will never have to pay
out a warranty claim. The testimonials at Canadian Tire appear to be from people
that take very good care of their cars, so how much of the car
durability can be attributed to fake CP systems. I think none, and I am
an expert in corrosion control.
TECHNICAL EXPLANATIONS and SCIENTIFIC Mumbo Gumbo
Electrostatic corrosion control technology
Cathodic Protection (Used in the earliest marketing literature, but dropped)
Electronic Rust Control Rustproofing
These scientific words are often used to answer the "How does it work?"questions. I believe the terms are made up nonsense. If the terms are real, they are misused or are used out of proper context.
The testimonials on the websites, product reviews and in car discussion forums can be explained by two simple and reasonable arguments.
The people that buy these devices are also people that clean and maintain their cars more than the general population.
Car manufacturers have improved the paint application process over the years, so many cars from 1992 and newer have less rust than old cars that we remember from earlier periods.
Senior VP Finance, Warranty & Operations
Manager of Dealer Support Team & CRM
These titles do not include jobs of corrosion control expert.
I see no difference between this system and systems sold under other brand names.