SAE recommended practice puts new shine on corrosion testing

  • 08-Sep-2009 12:29 EDT
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The corrosion problem has become worse over the past five to 10 years, according to J2721 sponsor Vern Caron.

A new SAE recommended practice (J2721 - Recommended Corrosion Test Methods for Commercial Vehicle Components) aims to improve the corrosion resistance of parts and assemblies used in medium- and heavy-duty trucks, trailers, and buses. The tests, with an emphasis on in-lab work, incorporate recurring conditions such as corrosive chemicals, drying, humidity, and abrasive exposure, as well as variations in the environment.

“Vehicle corrosion standards available today do not provide suitable coverage for new de-icing chemicals and application methods, nor do they adequately account for aggravating effects such as temperature extremes, abrasion, and mechanical stress,” said Vern Caron, Chair of the SAE Truck and Bus Corrosion Committee, which developed SAE J2721. “This standard was developed to address these issues and also to provide a methodology for evaluating laboratory results and correlating these results with field performance.”

Caron said there is great need for component suppliers to do accelerated testing. “And it needs to be done in a lab, although vehicle testing is OK, too,” he said, the latter more so for OEMs than for component suppliers.

Lab testing has the advantage of being cost-effective and, in most cases, better controlled and therefore more consistent than vehicle level testing, according to J2721. “And so the standard is really oriented around component testing that is accelerated,” Caron said.

Components at different locations on the vehicle require different tests, according to Caron, Director of Electronics for the ArvinMeritor Commercial Vehicle Systems group. “We needed to account for that, and this standard does.”

Caron and other industry corrosion-conscious engineers initially believed that a standard on brake corrosion was needed but upon further investigation saw that the corrosion problem on commercial vehicles was more widespread.

One of the decisions made by the committee was that components should be designed with corrosion resistance that will protect against worst-case environmental conditions. And so the lab tests provided for under the standard represent worst-case, if not necessarily real-world, conditions.

Caron said the next phase of the committee’s work will be to run sample corrosion coupons to “keep updating the correlation between what’s going on in the field with the lab results.”

This recommended practice does not address the chemistry of corrosion or methods of corrosion prevention. For information in these areas, SAE J447 is one source.

Corrosion on commercial vehicles has been getting worse over the past five to 10 years, according to Caron, and for many reasons. One is greater restrictions on the use of certain chemicals effective for corrosion resistance, such as hexavalent chromium, and greater use of certain chemicals by road departments to keep roads clear of snow and ice, such as magnesium chloride.

“Magnesium chloride sticks to vehicles more than sodium chloride does,” he said.

Another possible contributing factor to increased corrosion is that some component suppliers try to save costs by paring back on corrosion coatings with the idea that the OEM customer can coat the part. “Unfortunately, the material gets corroded on the shipping dock before the OEM gets a hold of it,” Caron said.

And, aside from actual causes of increased corrosion, there is the issue of heightened expectation of customers regarding corrosion.

“People are simply expecting things to last longer,” said Caron. “If you go back 20 years, we didn’t have brakes that could go to 500,000 miles. So, the perception is that corrosion is worse.”

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