Investigating Vehicles For Corrosion
May 2009, TruckingInfo.com - Feature
Rust! It's upon us like a plague, and has been since snow has fallen and ice formed on paved roads and authorities decided to try to melt as much as they could to make travel safer.
It's also a longtime problem on and near seacoasts where romantic "salty air" has an evil side. Rust - more properly called corrosion - is the oxidation of metals caused by salts and moisture, which combine to start a chemical reaction. Corrosion can also be the result of joining two different metals, typically steel and aluminum, which sets up destructive electrical activity.
Damage to vehicles began with use of common sodium chloride - rock salt - to melt snow and ice, and is worse with today's magnesium and calcium chlorides. Modern road salts are more aggressive, experts say, because the compounds adhere to metals more stubbornly and resist flushing, and continue working as long as there's moisture to be grabbed out of thin air. Aluminum and other relatively expensive metals naturally resist corrosion, but eventually are subject to it. Ferrous metals can be treated to resist corrosion, and are, and probably more such treatment with asphalt and zinc coatings should be done.
Damage to vehicles in general and commercial trucks in particular costs many billions of dollars annually. Corrosion is best caught early, before damage is extensive. Drivers should eyeball the lower areas of their vehicles, where salt spray is most intense, whenever they do pre-trip and post-trip inspections. Mechanics should check the areas around the parts they're working on, and perform careful periodic inspections according to company policy. The required annual inspection is one obvious time, but corrosion inspection should be done more often for vehicles that operate in cold climes where road salts are commonly used.
Components on trucks and tractors usually have a lot of heavy steel that can withstand salt assault for quite a while, but managers report damage that crops up surprisingly fast. One manager at last month's meeting of the Technology and Maintenance Council of the American Trucking Associations reported rust-through on axle carriers, so much that axle shafts inside began seeing damage, too. This was on a tractor only a few years old.
Some damage is obvious, but other is more hidden. Damage occurs on power units and trailers, especially among the many parts and pieces that are joined together in various ways.
Managers are so concerned about corrosion that eight of TMC's 13 Task Forces scheduled sessions on it during the annual meeting, and another session discussed how to proceed with information coming from those reports.
PM Time's Ideal
TMC members say an ideal time to find corrosion damage is during the preventive maintenance inspection, when a technician uses a checklist to go over the vehicle. Everyone knows what rust looks like, but corrosion isn't always a brown "rust color" that appears on steel. It can be the same color as the non-ferrous metal that the oxidation has formed on, or perhaps somewhat darker. Corrosion is often misshapen, showing a swelling or bulging that mars the once-uniform appearance of the metal. Corrosion also weakens metals and the parts they form, causing them to come loose from where they're attached and the vehicle to generally begin coming apart. As the inspector, whether driver or technician, moves along the vehicle, does he or she see any such damage? Is there a place on the inspection form to check off or write down notes?
Steering gear can stiffen up if neglected, and lack of lube grease at any point not only creates stiffness but also allows salt water to enter and begin attacking the parts. This is as true under the hood, where the column leads from the firewall to the steering-gear box, as completely under the truck or tractor's front end, where steering geometry is located. Does anything in these areas seem drier than it should be? Are there signs that the gear has been regularly lubed? How about the wheels - any signs of rust around lug nuts? That can mean damaged nuts and wheel holes. How do hubs look? Any signs of leaking seals or low lube oil?
Trucks and tractors have a lot of sensitive electrical and electronic parts that are especially susceptible to corrosion if splash and spray reaches them. Exposed wiring strung along frame rails and under the hood holds up well for quite a while, but breaches in insulation allow insidious damage to begin. Some wiring can be seen from above, others from below. The PM inspection should allow for both by separating the tractor from a trailer and allowing it to be parked over a pit where the inspector can work.
Many plug-type connectors are designed to keep out moisture, but they should also be positioned so water naturally falls away from where the two pieces join. Are they? Crimped or screwed connectors are often bare and most are under the hood or in the cab, under the dashboard. But they should be regularly checked for signs of corrosion. A bit of dielectric grease wherever wires are joined can help keep out corrosion and enhance conduction of electric current. Any connections inside junction boxes are supposed to be protected, and will be as long as the boxes have a good seal that has not been damaged. Are they? Electronic control modules are "podded" with urethane that keeps moisture away from microprocessors and circuitry, but problems can still develop at connectors that tie the ECMs with vehicle wiring. Any damage to any of them?
Trailer wiring should be looked after the same as that on tractors.
Here are a few tips from electrical experts on dealing with wiring and connectors:
• Never puncture a hole in wire jacketing, because it will allow chemicals to wick into wires and rot their innards. Instead, when tracing down circuits, work from the metal connectors.
• Remove build-ups of salt, especially magnesium and calcium chloride, by frequently brush-washing equipment during cold weather. Do not power wash, because water can be forced into areas from which it can't escape.
• After every cleaning, re-apply dielectric grease on plugs and socket pins.
• Clean connectors with a plug-and-socket brush and water (not soap) every six months.
Corrosion in Trailers
Probably the most dangerous place for corrosion in a semitrailer is its upper coupler assembly, the inverted flat plate that surrounds the kingpin and secures it to the rest of the vehicle. Corrosion that weakens the coupler structure threatens its ability to keep the trailer attached to the vehicle that's pulling it, whether tractor or converter dolly. This is why members of TMC wrote a list of inspection procedures specifically for the upper coupler assembly and included them in Recommended Practice 750.
A proper inspection requires the trailer to be parked on level ground and of course detached from the tractor, with the landing gear firmly on the ground. The trailer should be clean of grease and grime so everything to be looked at is plainly visible and easy to touch. Then the inspector can begin his or her work. This begins at the front of the assembly, just under the nose of the trailer. This is the leading edge of the coupler, where the tractor's fifth wheel begins sliding under the coupler. Some trailers have pick-up lips that extend a couple of inches forward from the front wall. How battered is it, and how strong? Tapping it with a hammer and pulling at it supplements what the eyes can see.
Now move rearward to the steel plate surrounding the kingpin. Any joints should be smooth so the fifth wheel can rotate freely as the vehicle turns; this is especially important for no-lube fifth wheels. Is the kingpin itself perpendicular to the surface of the plate? Is the kingpin tight, and is wear on its surface within tolerances? These can be ascertained by using a wear gauge available from manufacturers. What does the steel plate look like? Any crac