Wednesday, September 1, 2004
Corrosion Specifications, Where Do They all Come From?
As the world's aircraft fleet gets older, more and more technicians are using a variety of corrosion-prevention or -in-hibiting compounds to help protect and prolong each airframe's useful life. So it's not surprising that talk around the water cooler often turns to the subject of who is behind ensuring that these mystery chemicals really do what they're supposed to do.
"Testing of protective coatings goes all the way back to World War I when the U.S. Navy devised a salt spray test to evaluate the effectiveness of different paint coatings used on the exteriors of ships," explained Mark Pearson, general manager of Lear Chemical Research. "The aviation industry kind of picked up on that test through various military associations and that became the basis for today's mil-specs [military specifications]."
"B-117 [salt spray test] is a pretty basic test," he continued. "But it's been used for years. Today, the major aircraft manufacturers, Boeing, Airbus, Lockheed, and others have all expanded on that test and added specific tests of their own to qualify a variety of coatings including CPCs."
Pearson said that among the additional tests the manufacturers use to qualify products are functional penetration tests to determine a product's ability to seep between seams, lap joints, and other non-welded metal-to-metal bonds. They also use a displacement test that demonstrates a product's ability to displace moisture, which is the most important function of a corrosion-protection or -inhibiting compound.
And as the airlines and OEMs gain more experience with the causes of various corrosion problems on their airframes, they are becoming pretty darn creative with their testing requirements. "Airbus is notorious for having requirements to test for protection against a variety of things including orange juice, Coke, toilet liquids, body fluids, Skydrol, and just about anything that can seep down into the cargo area of an airliner," added Jason Smith, R&D lab manager and technical support for Zip-Chem Products. "They are really taking a close look at what elements their aircraft will be exposed to in everyday use and they want to make sure that the products they approve will do the job."
The key word there is "approve." While each of the OEMs wants to arrive at the same place--knowing products will do what they're supposed to do--each has its own set of tests to get the verification needed. In fact, there is a virtual laundry list of specifications and classifications for CPCs and CICs for both Boeing and Airbus, and let's not forget those military specifications.
Meeting military specifications or mil-specs is probably the most misunderstood of all the different nomenclature a technician has to deal with. Way back when, being mil-spec'd was as close to "universal" acceptance as you could get. Not any more. "According to the FAA, products such as those used for corrosion control must either be mil-spec'd or manufacturer approved," said Jim Van Gilder, president, Corrosion Technologies. "There is a catch because manufacturers probably won't consider products unless they are mil-spec'd; at least that gets you in the door.
"That said, companies like Boeing really don't care about [mil-specs or] any other approvals, because they create their own specifications," he continued. "All Boeing-approved products must be tested and approved by their own lab and then are assigned an ID number. They are not going to take a chance because of liability potential. They must test it themselves."
"The only advantage to having a product either mil-spec'd or pre-tested by an approved laboratory is that it will show Boeing or Airbus that it meets basic requirements and will not be a waste of their time to test," Jason Smith added. And it's not so much Boeing's time that you may be wasting; as a CPC supplier you could be wasting a lot of your money. "Boeing recently changed its approval process so that the product's manufacturer must pay its in-house lab to do the necessary test," he continued. "If it does pass, it will probably be added to their QPL [qualified products list]. But even then, there's no guarantee."
In fact, due to the rising cost and diminishing chance that your product may even make it on Boeing's QPL, fewer and fewer companies are bothering to invest the time and money it takes to qualify for the list. "Currently there are only two products that meet the latest Boeing BMS 3-35 specification for CICs," Smith said. "All but one of the Boeing fleet use the new BMS 3-35 specification, which is the replacement for the older BMS 3-23 and 3-29 products."
So does having only two products on Boeing's QPL list mean there are only two choices an airline can use on their current aircraft? Not at all. In fact, in the real world, the airlines are free to use whichever products they want, after all, they are their aircraft. "Just because we're on Boeing's QPL list, does that mean we'll get used by the airline customers?" Mark Pearson asked. "All that really is is an indication that the product meets certain performance requirements. It's the customer's choice whether or not they use your product in the end.
"Of course warranty issues can be a consideration by an airline, so they'll want Boeing `approval' to avoid problems down the road," he continued. "But, after the aircraft is out of warranty, they can do whatever they want."
Pearson added that all the OEMs' specifications and even the mil-specs are periodically updated to reflect regulatory or operational changes. "Mil-spec 81309 [the guidelines for corrosion-inhibiting compounds] is currently going through a major review right now," he said. "It was written in the early 1970s and now it's being rewritten through a cooperative effort between the users and the chemical producers.
"What the Navy and Air Force and others are trying to do is to create a `super spec' that will meet everyone's requirements," Pearson concluded. "When it's done, it will address a lot of issues that were missed in the last set of specifications simply because they weren't thought of then."
But, the question is, will this "super spec" eliminate the need for all the individual product testing and approvals? "Don't count on it," one supplier said. "All it will really mean is we'll have to go back and reapply for the various approvals all over again."
-- By Dale Smith