The Motherload

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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DetroiTug
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The Motherload

Post by DetroiTug » Tue Apr 23, 2013 5:13 pm

One of my local steam friends called and told me about some high pressure gas pipe at one of the local recycling yards. I went over this morning and took a look. It looks to be very good quality pipe 20" diameter X .310" wall and is tested to 2000 psi, it has all that stenciled right on it. There is a weld seam but it is almost invisible. Then there are the red ones which are 20" diameter as well but have an almost .5" wall. I bought three of those. It's like new with only surface rust. What do you guys think of this for boiler shell? Fred? I looked for any ASTM code #'s and didn't see any.

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Re: The Motherload

Post by fredrosse » Fri Aug 02, 2013 9:48 am

If the pipe specification and steel composition is unknown, then using this material for a boiler shell would not be recommended. The composition can be determined, but that can be costly. In general, boiler materials need to have very good ductility, (plenty of elongation before failure under stress), as well as proper chemical composition to adequately minimize the risk of various devils such as intergranular stress corrosion cracking and hydrogen embrittlement to name just two. If you can identify the actual material specification, then I would be able to check if the material is permitted for power boiler fabrication according to the ASME Code.

As a registered professional engineer I cannot recommend that the following paragraph be considered adequate to prove the worth of any material being used for a pressure vessel, however these methods were used historically to demonstrate adequate mechanical properties for steel and wrought iron boiler plates, boiler pipe/tube materials, and weld qualification. Similar tests were (and still are) used to see if steels might be OK for pressure vessel fabrication.

A section or test coupon is cut from the plate, about 2 inch x 10 inch, bent into a "U" shape, (180 degree bend), then flattened in a press, all without heat applied. The plate must survive this test without fracture of the steel outer fibers. For weld qualification, a test coupon is cut in half (two pieces 2 inch x 5 in), and butt welded with a full penetration weld, producing a weld test coupon, about 2 inch x 10 inch. If there was a weld backing plate used, it is ground off, then the same 180 degree bend and flattening test is repeated. This has been used to qualify the welds (and the welder).
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Re: The Motherload

Post by DetroiTug » Fri Aug 02, 2013 11:30 pm

That is an interesting tidbit. I bought three pieces of that pipe, the 1/2" wall stuff. It's high pressure gas pipe. I can't find a weld seam in it. That test would be somewhat conclusive. It was one of those deals where they were getting ready to crush it; matter of fact, it's all gone.

If nothing else, they would make a dandy culvert.

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Re: The Motherload

Post by Lopez Mike » Mon Aug 05, 2013 2:36 am

I dunno, Fred. There are an awful lot of boilers out there made from ordinary 1018 mild steel with very generous safety factors. I use well casing cutoffs for small VFT boilers regularly. I have one on my work bench that I have hydro tested to 500 psi just to show off. The shell is 8" casing. It would probably be safe at scuba tank pressures.

I know that to meet ASTM code these numbers and tests are needed but if such draconian standards were followed in our fleet, two thirds of the boats would be on the beach instantly.

Except for that brain damaged traction engine blow up in the mid west a few years ago, we haven't had a small boiler failure of any sort that I know of at all. That one had zero to do with design and materials and every thing to do with stupidity. Hard to guard against that. I've been paying attention to this sort of thing since the early sixties.

I like doing things right but sometimes it can get just too expensive.

Mike
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Re: The Motherload

Post by DetroiTug » Mon Aug 05, 2013 11:37 am

We should adhere and try to do things as close to the code as possible. I've had people ask me at shows "Is this type of boat legal?" Referring to the steam power. Note the general public sentiment. Thanks to Hollywood, every steamboat blows up, not an "if", but "when".

There has not been a serious steamboating accident in the US in over 100 years, from what I've read. This is the ONLY reason it's still legal. If one of us were to have a serious accident and the "news" hungry media takes off with it, which they will more than likely, we can all kiss our hobby as we know it, goodbye. At the stroke of a pen, it could be gone. We would be powerless due to our small numbers and limited resources to combat any such laws or mandates.

An 8" diameter pipe, the shear forces are low. On diameters of 20 and 24 inches, the shear forces are far greater.

Shear forces on the wall for 8" pipe at 150 psi is 3700 pounds, 24 inch at 150 psi is over 11,000 pounds. And that's per inch of length.

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Re: The Motherload

Post by fredrosse » Mon Aug 05, 2013 12:22 pm

Mike, everything you state here is true, and the remarks of Ron are, in my view, a salient response. I have spent many years in the Industrial Safety evaluation arena, and one must weight the level of safety applied to a machine according to its potential consequences. A pocket knife is dangerous, but the level of danger is small enough that we let a 12 year old kid have one. A handgun involves much more danger, and no children are permitted to have these! Hand grenades far more dangerous still, and no member of the public may have these. I agree that many alternate materials will, and do, work well enough, but as Ron points out, one newsworthy disaster might kill our playthings, so better to keep with proper design and proper materials if possible.

I have read (in LIVE STEAM no less!) the recommendation of using drill rod for staybolt material in a welded steel boiler. That would be a real disaster waiting to happen, although the author of that article probably thought "steel twist drills are really strong! I should recommend this for staybolt material". At least that mistaken material would not have passed the 180 degree bend test.
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Re: The Motherload

Post by DetroiTug » Mon Aug 05, 2013 1:10 pm

DetroiTug wrote:the recommendation of using drill rod
Drill rod or "Silversteel" as it's called overseas, is O-1 tool steel. It is "oil hardening" and is also considered an air hardening material by those of us who work with it on a daily basis. It is impossible to bend sharply without heating (as is 1018) and weld. When welded it crystallizes and becomes extremely brittle. If ample coolant is not used while drilling/machining it "turns to glass" as we refer to it. It will immediately smoke the cutter. Only solid carbide tooling will cut through and continue on.

1018 or "Cold roll or drawn" is the most commonly stocked and called for and sorriest of all steels to work with. It machines like lead, it can rarely be bent over 90 degrees without complete failure. It's only redeeming quality is that it is good for weld fabrications that require machining. As it is low carbon, it remains soft around welds IF allowed to air cool and anneal.

If a project requires cold bending, use 1014 or "Hot roll". For nice machine finishes in rolled steel, use 1040 and up. For shafting, 1045 or 12L14.

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Re: The Motherload

Post by Lopez Mike » Mon Aug 05, 2013 3:47 pm

Startling to hear of anyone recommend high carbon steels like drill rod for any welded application. I hope there was an instant outcry!

On that note, I'm sure we know what happens when one is foolish enough to try welding 12L14. I know, no one suggested any such thing, but many people read these posts.

The converse of having our hobby regulated to death because of an accident is to have it die from high expenses. I have no quarrel with a boilermaker charging what every he must for a code boiler but I would disagree strongly with our clubs requiring one. The cost of a code boiler would be a show stopper for many of us. To exclude potential steamers because they can't lay out tens of thousands of dollars for off the shelf hardware would be most unwise.

There is a tendency in many endeavors for things to escalate with time such that the barriers to entry in the hobby cause the activity to wither. I was a professional motorcycle racer over a period of forty years. At one point we began offering an entry class for stock street bikes. Within a short time, the people who had started racing in those classes started to push for more latitude in modifying their machines. They were increasingly successful in changing the rules. Soon, a beginner would just as well buy an expensive racing machine as do all the modifications to be competitive!

Personally I think that those pipeline off cuts would be just fine as VFT boiler shells. They are designed to be welded, more than strong enough and (not to beat the drum too strongly) inexpensive.

My preference is to have an experienced welder who has been, at some time, a pressure vessel an/or a pipeline welder do all of my serious boiler work. My most recent locomotive boiler was made of well casing cutoffs and a preforged offset reducer, all of which were rated to far, far beyond any possible needs. The welder did the root welds with TIG and the rest with 7018 stick welding. All starts and stops ground out. All joints beveled and welded with full penetration.

Our club requires an annual hydro test (1.5 times that safety setting) and safety valve demonstration as well as a visual inspection of the piping between the boiler and the first isolation valves. We have had one operator decline such a test and he was turned away from our events. He seemed to think that the hydro test would over stress his boiler!!!!!

I would submit that our water tube boilers need more attention to stress factors because of the greater diameter outer shell and the greater volume of stored water. I would resist a move to require a design review and materials list for construction. Between peer pressure, a few simple tests and self preservation, we have muddled along with nothing more than a very occasional leaky fitting or collapsed tube for decades. Our record is quite good.

Mike
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Re: The Motherload

Post by fredrosse » Mon Aug 05, 2013 6:54 pm

“Startling to hear of anyone recommend high carbon steels like drill rod for any welded application. I hope there was an instant outcry!”

In this case there was a follow-up article written in Live Steam Magazine by a person with better ASME Code knowledge, and the drill rod issue was properly exposed as a very bad idea. Several other features of the subject boiler design that were in violation of Code were also identified, and the original author’s rebuttal used the reasoning that “the boiler passed the hydro, did not blow up, so it is OK”. That kind of reasoning is very faulty to say the least!

I understand that Code boilers would be too expensive for many of us within our hobby, and there are many steam club organizations that conduct inspections and tests to provide reasonable assurance that some safety standards are followed. However even seasoned engineers do not know all of the pitfalls of boiler design and boiler materials selection. The ASME Code has spent countless hours developing rules, and examining details that might seem obscure to someone who thinks “steel is steel” without regard to its chemical and physical properties. Where possible, we should move toward following these rules. That is not to say that an armatures cannot build a strong boiler, but when better information is available, we should move in that direction.

“I would submit that our water tube boilers need more attention to stress factors because of the greater diameter outer shell and the greater volume of stored water.”

I think you meant to say “Our firetube boilers” Yes? I have to disagree here, either boiler rupturing can spoil your day, and while the firetube types typically have a larger water inventory, and larger shell diameters, proper design and stress levels should be followed. We should not relax our attention because a boiler is of one type or another.
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Re: The Motherload

Post by Lopez Mike » Mon Aug 05, 2013 7:30 pm

Yes, I meant fire tube. Senior moment.

I do a fair but of scrounging about in scrap yards and I have yet to see any larger diameter tubing that wouldn't be safe for a properly designed boiler. I suppose there must be some unsuitable stuff out there but I haven't seen it yet. It all seems to be either well casing or pipeline cutoffs. Nicer stuff than I would come up by rolling up some flat stock and doing a longitudinal joint.

I, too, would not want to encourage poor design and false confidence but I do think that there is much more margin of strength in the average launch boiler than is commonly realized.

Also, I am received of regular alarms about warming up my boiler too fast. Now this a steel boiler with welded in tubes. In the process of construction, small areas were raised to the liquid point of steel while inches away the material was at ambient temperature. The idea that I am going to hurt it with a wood fire is entertaining. Except for the wood lagging, I would venture to say that my boiler, when empty of water and under no internal pressure, could be raised to near glowing temperatures without anything but some stress relief from the assembly welding.

Same thing for blow down. Mine has a laughably over sized blow down fitting. 1.5" pipe on a 30 square foot boiler. As soon as the fire has burned down to coals, I feel quite safe in just opening the valve and blowing it down hot. It is an old wife's tale that the pressure jumps to some high level on release of steam, however rapidly. The physics just aren't there. The conversion of liquid to vapor during a progressive shell failure is more than sufficient to produce the dramatic damage we see in accidents.

Mike
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