USS Seawolf (SSN-21) hydrogen cracking

The Nautilus was the first ship that had HY-80 in it, sometime in the '50s. They had all kinds of hydrogen cracking problems, such that some of the first subs they actually welded with austenitic stainless steel, because they couldn't solve the hydrogen cracking problem. It took them about 10 years to really get their arms around that, and then they had the Thresher problem and they had Subsafe. They didn't actually start putting HY-100 into ships until the late '80s. There were two ships before the Seawolf that they put modules — cylinders in the center of the ship — with HY-100. I'm familiar with that because my first student ever still works at Electric Boat as a welding engineer. He was in charge of welding up those HY-100 cylinders. When the Seawolf had all its cracking problems, the two captains who were in charge of the ships came to me and said, well, what about our two ships with the HY-100 that are out there? I said, don't worry about it, just inspect them when they come back in. They're not going to fall apart tomorrow — but they could fall apart if you didn't inspect them properly.

Tom's personal arc with Millard Firebaugh through the Seawolf program — funding zeroed when Soviets fielded titanium submarine; consulting role after 18% of ship had to be torn apart and rebuilt.

I had students who, when they became captain, were head of the program for the DDG 51, and then the Zumwalt class that just got cancelled. Millard Firebaugh was before my time. He was a 13A, which was before 2N, and he got a PhD here. He was in charge of designing the SSN 21, the Seawolf. I knew him when he was a captain designing the Seawolf. I knew him when Congress zeroed the budget for the Seawolf because the Soviets had developed a titanium submarine and Congress said, oh, they've leapfrogged us. I knew him when he went back up to the Hill to get the money back. I knew him when he became chief engineer of the Navy. And I was hired by him when they had completed 18% of the ship and had to tear it all apart in the early '90s, along with a few other people, to look over Electric Boat's shoulder and make sure they didn't make the same mistake the next time. He's still alive, retired obviously now.

Brief reference. Hydrogen cracking still happening 70–80 years after Stout wrote the book on how to avoid it. "People still don't follow the welding procedures."

The steels generally don't have this BCC heat-affected zone equation, because iron-based alloys just don't have this. I have seen weld solidification cracking when you're trying to weld over a high-phosphorus paint. The problem they reproduce is hydrogen-induced surface cracking, and we're going to go over that as a base case, because I've seen this half a dozen times even though Stout wrote this book about how to avoid hydrogen-induced cracking. Seventy, eighty years later, we still see the Sea Wolf submarine that I talked about have hydrogen-induced cracking.

Cited to make two points: (1) the redone Sea Wolf used high preheat plus the "blue jelly suits" humidity control to prevent recurrence; (2) the Sea Wolf cracking was unusual in that it occurred in the weld metal rather than the heat-affected zone, because of overmatching weld metal strength. Tom notes Electric Boat shut down production for about a year and salaried workers still had to be paid.

The highest temperature I've ever seen in steel preheat is about 600, and that's for a very thick highly restrained steel. Most steels are not above about 400. But even though I told you about the Sea Wolf and the blue jelly suits, when they redid the Sea Wolf they didn't want to have it crack a second time, so that's why they went to the blue jelly suits. They actually, I think, shut down production at Electric Boat for about a year. Even that cost a few dollars, because you might be able to lay off the hourly workers but you can't lay off the salaried workers — they still got to come and eat their lunch in the cafeteria. Actually they had a lot to do trying to figure out how to solve the problem.

The principal forensic case of the lecture. The Seawolf was supposed to be welded with HY-100 (100 ksi) steel, but high-side chemistry on every alloying element (carbon, manganese, chromium) drove the weld metal strength to 130 ksi with martensitic rather than acicular-ferrite structure. Hydrogen cracking ensued. Repair cost an additional $2 billion, doubling the submarine's price; Congress was unhappy. Only one Seawolf-class was built, partly for this reason and partly because the Cold War ended.

You're not Navy folks, but this summer when the Navy guys have to watch some of these lectures — that's what happened to the Seawolf submarine. The Seawolf was supposed to be welding HY-100, but they had a weld metal that was a little too rich in chemistry. They said high-side chemistry — the carbon was at the maximum of the range, the manganese was the maximum of the range, the chromium, everything was at the maximum of the range, and they were getting 130 ksi weld metal. It was more of a martensitic structure rather than acicular ferrite, and all of a sudden they ran into all kinds of problems with hydrogen cracking. Cost an additional $2 billion for one submarine. Congress was not happy. The submarine was supposed to cost $2 billion, not the repair. So it doubled the price of that sub. I think we only built one Seawolf, or one of the Seawolf class, but that was also because peace had broken out with the former Soviet Union and we didn't need a submarine that would be able to shoot down Soviet submarines.

The weld metal ran 30–40% higher strength than intended because of carbon and alloy content; toughness dropped; 1 mm microscopic flaws formed that the original inspection wasn't looking for; a grinder noticed magnetized swarf aligning with the cracks, an inspector was called, and every weld in the sub had to be cut out. 18% of the ship had been built. Cost the Navy $2 billion.

Even with prototype experience, Sea Wolf hull welding had major problems. In §7 the case is developed: they thought they had HY100 filler but got HY80-equivalent due to property scatter, hydrogen control inadequate, 18% of the ship welded with undermatched filler.

This is another problem with our pressure vessels. You guys still use ASME pressure vessel steels. Almost all of those were developed in the 1940s, and it would cost probably half a billion dollars to qualify new steels for pressure vessels. The Department of Energy has tried to qualify 9% nickel steel — sorry, nickel-1-molybdenum — to use at higher temperatures for some of the nuclear reactors. They've been doing this for 40 years, and people are still somewhat hesitant. They haven't got a big enough database out there until you actually start building prototypes and get experience. That's why the Navy, before they went to an all-HY100 hull, built a couple of full-size 30-foot-diameter sections for a couple of boomers back in the 90s and put them in service, even though they were still on HY80. They wanted to get the experience with welding it. And even when they did go to a full-sized ship — Sea Wolf in the 90s — they still had major problems. One of the reasons for building things like Alvin and the Sea Cliff was as part of the prototyping research exercise. You build small submersibles, deep-submergence things, but it also gives you experience with fabricating what they hoped would be the next HY-series alloys.

Brief closing reference: Captain Millard Firebaugh (a graduate of MIT's program) was designing the SSN-21 in the mid-1980s when Congress zeroed the next year's budget, saying they wouldn't build another steel sub while the Soviets had titanium subs — and that the U.S. should leapfrog to composite submarines. Tom mentions attending a four-day workshop on composite subs which he calls "a laughing mess." Setup for a future lecture.

In the end, the U.S. Navy was right to be as cautious as they were. You could build one titanium sub for ten steel subs, so you have to ask yourself, would you rather have ten steel subs or one titanium sub? There are little trade-offs like that. Anyway, the Navy decided not to build titanium subs. Congress was livid that the Soviets had leapfrogged us. I can tell you other stories over the next five years about how Congress took away all the money for the SSN-21 when Millard Firebaugh was Captain — he was a graduate of your program — but he was designing the SSN-21 in the mid-1980s, and Congress zeroed his budget for the next year. They said, we will not build another steel submarine while the Soviets have titanium submarines, and we don't even want to build titanium submarines — we want to leapfrog, we want to build composite submarines. I went to a four-day workshop on that, and that was a laughing mess. Anyway, we'll see you tomorrow.

The lecture's centerpiece case. Tom's consulting role on the Seawolf HY-100 cracking investigation. Key elements: high-side wire from Lincoln Electric meeting spec but at the upper alloy bound (producing 130-140 ksi weld metal); 5-15 ppm hydrogen vs. the 2-3 ppm tolerable at that strength; Tom's drawing-lubricant hypothesis based on hydrogen scaling with wire surface-to-volume ratio (1/R); the Crystal City meeting with two Navy captains; in-his-head fracture mechanics calculation showing critical flaw size >> existing sub-eighth-inch flaws, leading to "don't derate, do more inspection" recommendation.

So let's go back to what happened with the Seawolf. They were welding HY-100 in the Seawolf. It was the first full-scale submarine with HY-100. They'd been welding HY-80 for forty years, successfully for thirty of those forty years. The first ten years were a little hairy. Whenever they switch to a new steel, they have all kinds of problems. They'd built two modules. Submarines are built in modules. Say it's thirty feet in diameter and a module is thirty or forty feet long. They can lift these whole modules — they might weigh five hundred or a thousand tons. They have big trains to move them. Building in modules speeds up production and saves money. They had built modules and put HY-100 modules into HY-80 hulls because they wanted the experience. My first student ever, John Galligan, was working at Electric Boat, and he was assigned the responsibility to build the first HY-100 module hulls — not for the Seawolf, but for the couple of ships that preceded it.

1992 discovery by a grinder noticing sixteenth-of-an-inch swarf alignment from sub-eighth-inch cracks the inspection equipment couldn't reliably find. $2B repair, 18% of hull complete at discovery. Tom was one of two individual advisors to Admiral Firebaugh, then-Chief Engineer of the Navy. Used to teach: critical flaw size in the steel is several inches; the sixteenth-inch cracks are below the detection threshold; you don't have to derate the submarines, you just inspect for growth at scheduled maintenance.

To give you a specific example: in 1992 the US Navy was building a two-billion-dollar submarine down in Groton, Connecticut, called the Sea Wolf — the 21st-century submarine. It had been designed by Captain Millard Firebaugh, an MIT grad who got his PhD in what's now Course 13, then Ocean Engineering. He was in charge of designing the Sea Wolf in the 1980s, when I first met him. They built it in 1992. A guy was grinding the outside surface of the hull. The hull has to be about 30 feet in diameter, plus or minus a quarter of an inch, smooth. Little ripples of a quarter of an inch — like weld reinforcement — create sonar noise, and they'll find you. So a guy was grinding this and he noticed, as he was grinding, the swarf — anybody know what swarf is? If you like Scrabble, that's not a bad Scrabble word. Swarf is the particles that come off in grinding. He saw the swarf was lining up in sixteenth-of-an-inch lines. The welds were full of little sixteenth-inch cracks, and they hadn't found them. They had done their inspections, but their equipment is designed to find an eighth of an inch and larger, because that's what the standard says, because that's what you can reliably find. He noticed it, said, I've never seen that before, told somebody, and they found the entire submarine — eighteen percent of the hull was completed — full of these little cracks.

Two-billion-dollar Navy problem traced to welding wire drawn from an enriched (high-side-chemistry) region of a twenty-ton ingot. Yield strength came in at 140 ksi instead of 100 ksi; hydrogen sensitivity scaled accordingly. All within spec but at the wrong end of the range. Used to land the teaching point that microsegregation in the original casting propagates through downstream processing.

Why can that be a problem? The whole Sea Wolf problem, two billion dollars it cost the Navy, was because the welding wire was too rich. It had too much of certain alloying elements, and it probably came from an enriched area of the casting. It was all drawn into wire, but they didn't draw the whole twenty-ton ingot into wire all at once. They cut it up in pieces, and so this part of the ingot was rich, this part was poor in alloying element. The lot they used turned out to be what they called high-side chemistry. If you had gone to that same ingot, you would find low-side chemistry elsewhere. The problem with the high-side chemistry: it had a yield strength of about 140 ksi, not 100 ksi, because it was enriched in alloy. At 140 ksi, your sensitivity to hydrogen is much worse. You can't tolerate anywhere near as much hydrogen. It was all within the Navy spec range, but it happened to be all the way at one end of the high-side chemistry. They always give you a range because there are these inhomogeneities in the casting. They got bit by segregation all the way back in the original ingot. Some of these things actually are important, and they do follow through the whole system and can sometimes create real problems for you.

A grinder smoothing welds on the first Seawolf-class submarine noticed grinding swarf lining up in lines under a sixteenth of an inch — a flaw size below anything the specification had ever required inspectors to find. Destructive sampling revealed clusters of micro-cracks throughout the welds; 18% of the hull had been completed. Tom contributed to the investigation report and identifies the weld-wire chemistry being on the high side as a contributing factor. Repair costs Tom heard ranged from half a billion to ~$2 billion — comparable to building a new boat. Two Seawolves were built before the program was canceled with the end of the Cold War. Tom uses the case to dramatize how improvements in measurement capability create disputes about flaws the original specification never contemplated.

So what happened to the Seawolf submarine? They were looking for eighth-inch flaws. That's what the codes say. That's what reality says is all you can find with any probability. But what happened is some grinder was grinding the weld smooth. On a submarine you can't have these big humps of a weld when you're going through the water — it's amazing how quiet these things have to be. They have to grind the weld flat. This grinder grinding the weld notices that the swarf — the little particles from grinding, called swarf, good Scrabble word, S-W-A-R-F — the swarf is lining up in little lines, less than a sixteenth of an inch in length. He says, I've never seen that before. He goes and tells someone, and someone says, hm, I've never seen that before. They start investigating it, and the welds had a whole family, a cluster — they were full of these little micro-cracks.

One-sentence flag — "I can tell you a story about welding of the Seawolf submarine, and I tracked it down in my opinion to lubricants." Tom does not develop the case here. The hydrocarbon-as-hydrogen-source point is what's being illustrated.

Now where does the hydrogen come from? What's the largest source of hydrogen in the world? Water. The ocean. It doesn't come from the ocean, but it does come from moisture, because moisture is everywhere too. So one of the key areas is moisture. What else contains hydrogen? Hydrocarbons contain hydrogen. So any grease or oil that's around, lubricants — I can tell you a story about welding of the Seawolf submarine, and I tracked it down in my opinion to lubricants. The moisture can even be humidity in the air. So one of the common things — and we'll talk about it some more — are stick electrode coatings.

Around 1992 at Groton (Electric Boat), the Navy moved from HY-80 to HY-100 for the Sea Wolf hull. A grinder noticed swarf lining up along sub-eighth-inch cracks in completed welds. Re-inspection found all welds (18% of hull complete) full of microscopic hydrogen cracks. Required scrapping the completed portion, delaying the program a year and costing ~$2 billion. Fix: preheat the steel to 400°F, with welders working in recirculated-liquid blue jelly suits inside heated submarine compartments.

Hydrogen embrittlement occurs all the time. The US Navy down in Groton was going to a higher-strength submarine steel, from HY-80 to HY-100. Didn't seem like a big change. They had promised Congress in the early nineties that they would eventually start making the 21st-century submarine out of HY-130, which they developed in the 1960s, but they never had the nerve to actually build a whole ship out of. So they're starting to build a whole ship out of HY-100 — this is the Sea Wolf, the first edition of the 21st-century submarine, around 1992. Higher strength by 20 ksi, going from 80 to 100 ksi yield strength. The inspectors look for flaws an eighth of an inch in size or larger, and they found none in the welds. Some guy's grinding the surface of the hull to make a smooth contour — you can't even have a little weld reinforcement, because going through the water it creates enough noise that they can pick it up on sonar. So they have to grind it smooth. This grinder noticed that the grinding swarf, the little iron oxide particles, was lining up in these little less-than-eighth-of-an-inch-long parts in the weld metal. He was smart enough to tell someone, and they came in and did more thorough non-destructive testing — and all the welds, 18 percent of the hull had been completed, all the welds were full of little microscopic cracks they had never seen before.

Tom's role as one of five outside experts brought in by the Navy in 1991–92 to advise on the Electric Boat HY-100 weld failures. His report uniquely concluded the cause was dirty welding wire (drawing-lubricant contamination, worse on smaller-diameter wire due to higher surface-to-volume ratio). Eighteen percent of the hull was riddled with sixteenth-inch under-bead cracks in weld metal, discovered when a grinder noticed swarf aligning magnetically.

Two prior 688-class attack submarines had 20–40 ft HY-100 test sections built into them as a precursor to Seawolf. After the Seawolf cracks were found, the Navy asked Tom whether those existing ships had to be derated. His answer: no — increase inspection budget, the sixteenth-inch cracks won't grow fast enough to threaten ship life.

When they had the problem with the Seawolf submarine, these guys had to go into enclosed containers where the steel had to be at 400 degrees Fahrenheit to prevent the hydrogen cracking. They had to wear blue jelly suits. They were only allowed to be in there for like twenty minutes at a time. So they'd have a little cart like a mechanic's creeper to go underneath a car, and they'd roll them in there, and they'd have to have someone outside because this was a confined space. They called them blue jelly suits — they had to wear this suit that had this blue liquid in it that would cool them down, because they were going into a 400 degree oven to do their welding. And they had respirators so they could breathe cooler air so they wouldn't burn up their lungs. They'd go in for like twenty minutes and then have to come out and have a rest, and another guy would go in there. It got a little expensive to build that submarine. But it's because they had too high strength and didn't have good enough hydrogen control.

Used as an illustration of hardness above Rockwell C40 producing hydrogen cracking — the weld wire was within spec but all alloying elements were at the high end of the range, producing effectively HY130 weld metal.

Hardness Vickers is about Rockwell C40, and 350 is about Rockwell C35. I told you in general you have a hard time getting cracking below Rockwell C30. Once you start getting into this 35 to 40 range, that's the problem with the HY130 Seawolf welds. I call them HY130 — the weld metal was sort of an HY130 weld metal. They were up there above Rockwell C40, and that's why they're getting hydrogen cracking. It was within the specification range for the welding wire, but it was on the high side. All the carbon was at the high end of the range, the chromium was the high end, the nickel was the high end, the vanadium, everything was the high end. So it really was an HY130 weld metal, it had crossed the line, and you could get very high hardness.

Brief reference. Source of lessons on welding high-strength steels. Used as a parallel to the Thresher in Petroski's framing of "we learn from failure."

Henry Petroski, a guy at Duke University in the civil engineering department, wrote a book called To Engineer is Human. He's gotten famous off it, elected a member of the National Academy of Engineering. The book is about how we learn to engineer new structures from failures. We learn from the Sea Wolf problem — expensive lesson to learn, but we learned a lot about welding high-strength steels we didn't know about. We learn about process control from the Thresher — the whole SUBSAFE program came out of the Thresher disaster.

Sea Wolf submarine MIG (gas metal arc) welding hydrogen problem — no flux to suppress hydrogen pickup.

It shows up with all processes. The Sea Wolf submarine, the problem was with MIG welding, gas metal arc welding, where you had no flux. I'll show you a plot of how much hydrogen you get with different welding processes. So we're going to spend a fair amount of time on steel. We will get to aluminum, but that'll be probably next week. Let's take a break until about 8:39.

Recap from an earlier session. Over-matching by 30–40% combined with insufficient preheat for the resulting higher hardenability. Used here as the lead-in to the Helms Project — "this still occurs on a fairly regular basis."

I'm going to start giving you some examples of classical failures. We've talked about the Seawolf. On the Seawolf they ended up with a very high material strength in the weld metal — too high. It was over-matching by about thirty or forty percent. You ended up not necessarily with an inherent problem in the weld metal, but with higher stresses and higher hardenability, and they didn't have enough preheat for that higher hardenability to get the hydrogen down to a low enough level.

When the problems are really big you can often go around the attorneys. But when the problems are smaller — say, a hundred-million-dollar problem — the attorneys take control, and then you can't get the engineers together. No one wants to allow their engineering staff to talk to the others. It's pretty dysfunctional as far as solving the problem, because everybody's CYA — who's going to pay for it? When the Seawolf submarine had its two-billion-dollar problems with the welds, they worked it out. What are you going to do? You're going to bankrupt one of the two submarine building facilities? You can't do it.

Tom's full forensic case — he traced the cracking to lubricant contamination in the GMAW weld zone. To repair, Electric Boat used cooling-suited welders ("blue jelly suits") on wheeled carts to work inside egg-crate construction with 400°F preheat. Forced reuse of the heavy plate because four-inch plate was on a >1-year mill backlog.

In fact, the Seawolf submarine had hydrogen cracking. I actually determined it was hydrogen due to a lubricant in the gas metal arc weld zone — not cleaning the lubricants off well enough. That was my conclusion. Electric Boat didn't like hearing that, because they had it left over from a previous job. When they started to repair it, they first had to dig all the welds out and then start re-welding. Congress was not happy at the time with two-billion-dollar problems. They actually started welding in what they call blue jelly suits. The foundations of the submarine are pretty heavy steel, a lot of it in egg-crate construction. You're crawling into some hole, and they wanted you to preheat to 400 degrees Fahrenheit. How would you like to be the welder in egg-crate construction underneath that? They actually put the welders on little wheeled carts, like a mechanic uses underneath a car. They put them in blue jelly suits, pumped chilled liquid through them, they were breathing air through a mask, and they had like ten minutes of welding time before they had to come out and someone else had to go in.

Sea Wolf welding wire chemistry was on the high side of every alloying-element range, producing weld metal that behaved like HY-130 rather than HY-100. Cracking resulted. Repair required 400°F preheat with welders in cooled "blue jelly suits"; $500K hull required $2B repair.

In fact, when they redid the Sea Wolf in the early 90s, the problem with the Sea Wolf is they were using HY-100.

Student: Which is what composition?

Same as HY-80, just tempered at a lower temperature to retain a little more strength. But the weld metal was much higher, and it was on the high side — all the alloying elements were kind of high. You have a range for each alloying element; the carbon might be between 0.08 and 0.16. Well, what did they have for the carbon? It was 0.15 — is that the high side? The chrome was supposed to be 0.2 to 0.3, and it was 0.29. Every heat of steel that they made the welding wire out of for the first 18 percent of the vessel was on what we called a high-side chemistry, and it was really more like an HY-130. They should have been doing HY-130 welding procedures, because the weld metal was basically HY-130, and that's why they got cracking. That and some other things which we can talk about later. But that's why you try to keep your alloy content down as low as possible — to save money and to make welding easier.