Boeing 747-400 catalytic converter titanium welding failure

Engelhard NJ contractor cannot produce porosity-free titanium ductwork welds for the catalytic converter. Tom diagnoses oil residue from commercial-grade acetone; reagent-grade acetone solves it. Reagent-grade compliance lapses; problem recurs; cleaning discipline solves it again.

In fact, you don't have titanium welds that don't have a little bit of porosity. Some of these things can be ten thousandths of an inch, and that's the Boeing story I'm going to tell you about. When Boeing was coming out with the 747-400 — this is the extended range, lighten the weight, increase the fuel capacity, an extra thousand miles, because at that point they were at eight or nine thousand miles, and you'd like to have 11,500, which is the mileage on a great circle from the two largest cities, the greatest distance on a great circle for major cities of the world. Kind of like going from New York to Sydney, Australia. There are only a couple of routes. You'd like to be able to supply that distance, and of course you have a little safety factor in case you get weather.

Engelhard contracted to weld thin-walled titanium ducting for ozone catalytic converters on the 747-400. Boeing's spec required no flaws larger than ten thousandths of an inch on x-ray. They were failing one out of two welds. Tom diagnosed contamination from commercial-grade acetone and fingerprint oils; reagent-grade acetone and white gloves got them to ninety percent. Problem recurred when they slipped back to old process. **Central case of §5.**

Titanium is a different animal in terms of the cleanliness that's required to get good properties. You do have to clean it well. I guess I'll tell a Boeing story. Actually it's not a Boeing story, it's an Engelhard story. I'd just come back from Japan, maybe it was late 80s, and I get a phone call. They were about to roll out the 747-400. So if we went back and found out when the 747-400 — the dash series, this dash 100, 200; I think we're up to 747-800 now. They improve them every now and then. They were going to come up with a longer-distance 747.

Engelhard making titanium catalytic-converter housings for cabin air ozone treatment. Boeing's x-ray spec called for no flaw > 10 thousandths — a limit chosen by NDT detectability, not by any analysis of the service application (low-pressure air). Half of all welds failed; with four welds per part and one allowed repair, virtually nothing could ship. Tom diagnosed the spec as bureaucratic CYA.

There's another reason for bulking up safety factors. Around 1990, I'd taken a trip to Japan, and I got back in my office and had a note to call Engelhard — which makes platinum. They needed me to come down because they were making titanium housings for catalytic converters going on the new Boeing 747-400. The 747-400 was a lighter-weight 747, redesigned to take thousands of pounds off so they could put thousands of pounds more fuel and fly direct flights to further distances. The first time I ever went to Japan, we always had to stop and refuel in Anchorage, Alaska — you couldn't make it all the way to Tokyo from the West Coast, or even the East Coast. Now you can get direct flights on the new 787 from New York to Tokyo, which we never could before. As planes get lighter with more fuel and more fuel-efficient engines, you can go almost halfway around the globe — which is as far as you need to go, unless you're the U.S. Air Force.

Engelhard was building a titanium catalytic converter (for cabin-air ozone removal) for the 747-400 long-haul jet, replacing a stainless steel design to save weight. Boeing's spec disallowed any flaw larger than 10 thousandths of an inch — about four human hairs — which Tom shows was a CYA spec written by someone who set acceptance criteria at the limit of x-ray detectability rather than at any engineering-based size. With a 50% reject rate on four required welds and one repair allowed, statistics doomed throughput. Tom's diagnosis: 55-gallon-drum acetone left an oil film causing hydrogen porosity; switching to reagent-grade acetone dropped rejects from 50% to 10%. Engelhard reverted to old practice twice and had to be re-told three times.

About twenty years ago, I came back from a trip to Japan, I'd been gone one or two weeks. I get back and I have a note on my desk to call this company down in New Jersey — I think it was Engelhard, makes precious metals. They were building a catalytic converter for the 747-400. The 747 comes in different dash numbers — they're up to the dash 900 now, but back twenty years ago they were building the 400, an extended-range 747. You can be even more miserable on an eleven-hour flight than a nine-hour flight. The first time I ever went to Japan we had to stop in Anchorage, Alaska, because you couldn't go all the way across the Pacific. They did a great circle, you'd stop in Anchorage, you'd see this big stuffed polar bear, hang around for an hour and a half, then they'd refuel the plane and you'd get on. With something like the 747-400, you could go from Los Angeles to Sydney, which is one of the longest city routes on a great circle in the world. There are two or three longer, but now the 787 Dreamliner can do any of them, unless you're the Air Force and you want to go all the way around the world in one trip without refueling.

Air tubing switched from stainless steel to titanium to save weight for the extended-range 747-400; Engelhard built the catalytic converters for ozone scrubbing in the cabin air system. Introduced here mainly as a vehicle for the aircraft-range discussion (10,000 → 13,000 mile aircraft) rather than as a developed failure case. Tom flags it as a long story not fully told.