Schedule 80 pipe?

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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Schedule 80 pipe?

Post by DetroiTug » Fri Oct 14, 2011 4:00 pm

I recently suggested someone use schedule 80 pipe on the main steamline, and any piping carrying boiler pressure on our small steamboat applications. And received a reply that if it's not over a 250 psi system, that schedule 40 is ample and purchasing sch 80 is just wasting money. Also "All iron pipe is rated for steam" ?

I spent about an hour researching the ASME code regarding power boilers ANSI/ASME B 31.1. I can't make heads or tails from any of it, not in an hour anyway. It appears that the code does mention Schedule 80 over 250 psi. But, I'm wondering if that is strictly for stationary boilers, not our portable boilers being trailered and subjected to engine vibrations etc.

For myself, I'll always use schedule 80 from a fatigue and corrosion standpoint. Simply looking at schedule 40 threaded pipe components reveals in the threaded portion at the thread root, the wall is very thin. And of course most of these schedule 40 iron components (practically all made in China now), they are very crudely made. I simply would not trust them from a safety standpoint.

-Ron
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Re: Schedule 80 pipe?

Post by artemis » Fri Oct 14, 2011 5:43 pm

DetroiTug wrote:...For myself, I'll always use schedule 80 from a fatigue and corrosion standpoint. Simply looking at schedule 40 threaded pipe components reveals in the threaded portion at the thread root, the wall is very thin. And of course most of these schedule 40 iron components (practically all made in China now), they are very crudely made. I simply would not trust them from a safety standpoint.

-Ron
In Portland, OR I deal ONLY with Paramount Supply for my pipe, valves, packing and gasket materials. They carry US or Canadian made valves and pipe and will cut and thread pipe for a nominal fee. Their pipe dies are clean and sharp. Only once in 15 years have I ever had one of their threaded joints leak. Valves and fittings meet US requirements. Castings from Taiwan, China, etc may have impurities in the castings - I remember a friend who needed to drill a small hole in a brass valve casting. Broke a 0.1875" drill bit (held in a drill press) off on a piece of steel that was in the casting! Arrgh! As to the Schedule 40/80 discussion: cost of pipe from a supplier is by the pound. There's not a lot of difference in cost in the small (relatively speaking) quantity of pipe we use, and I personally know of one instance where a Schedule 40 x 1/2" x 2" pipe nipple from the boiler to the whistle stop valve was leaking badly (steam blowing by the valve connection). Upon attempting to remove the valve, the end of the pipe in the valve broke off easily when a wrench was applied (I did the wrench work and not much more than the weight of a 16" pipe wrench was all that was applied). And this nipple was not directly exposed to the weather. I ALWAYS use a thread compound like "Neverseize" for ALL threaded connections - pipes, machine screws, nuts, any threaded fastening - soak 'em in salt water and they still come loose easily.
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Re: Schedule 80 pipe?

Post by fredrosse » Sat Oct 15, 2011 1:27 am

The ASME Code, as well as the Power Piping Code B31.1 both allow carbon steel schedule 40 (and even lower schedules) for high pressure steam service, however there are formulas as to what allowable temperatures and pressures go with the pipe materials, the materials allowable stress, wall thickness reduction due to threading, etc. These Codes require the stress analysis not only for the steam pressure stress, but also the forces and twisting moments on the pipe. In summary, unless you have these types of pipe stress analysis performed, you are operating in unknown regions.

The company I work for builds power plants, and can do all of this analysis, however we have a firm rule that all piping below 2 inch IPS must be schedule 80 or heavier. This is to lessen the risk that someone standing or leaning on a small pipe will overstress the piping, especially threaded piping. Schedule 80 piping, and 300 pound rated cast iron (or steel) fittings cost a little more, but provide a margin of safety that can easily be worth much more.

One of the most stressed pieces of pipe on typical steam launches is the pipe between the boiler and the engine. This piping should have an adequately sized stress loop, and if you don't have an analysis for this, then you can buy a braided stainless flexable coupling that can take most displacements, and is rated for 150 - 300 PSI at over 1000F. I use two of these on my sidewheeler, 1/2 inch IPS from W.W.Grainger, each is about 8 inches long, they cost about $22.00 US each.

Of course, there are braided stainless hose assemblies (with rubber or plastic hose inside the stainless braiding) that are sold for sink and lavatory water supplies, but these are not rated for steam service, be sure you get hose assemblies rated for your steam temperature and pressure.
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Re: Schedule 80 pipe?

Post by barts » Sat Oct 15, 2011 4:11 am

Schedule 80 pipe is mandatory for all boiler/steam connections. This is because the threaded schedule 40 stuff will fail too easily due to a mechanical mishap. I stick to schedule 80 for the feed connections as well, of course. Inside the boiler, you can use schedule 40 when it is used as tubes.

- Bart
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Re: Schedule 80 pipe?

Post by farmerden » Sun Oct 16, 2011 4:23 am

I needed a sched 80 3/8" pipe nipple when I replumbed my boiler.My local plumbing wholesaler did not have it but the hydraulic hose company had it in stock.Cost -under $2 -pretty cheap insurance! I have a saying-"we poor people can only afford to do it once-so do it right the first time!" At least I think I said that!! Den
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Re: Schedule 80 pipe?

Post by barts » Sun Oct 16, 2011 4:39 am

farmerden wrote:I needed a sched 80 3/8" pipe nipple when I replumbed my boiler.My local plumbing wholesaler did not have it but the hydraulic hose company had it in stock.Cost -under $2 -pretty cheap insurance! I have a saying-"we poor people can only afford to do it once-so do it right the first time!" At least I think I said that!! Den
Yup... in fact steel hydraulic fittings work quite well and, being rated typically at 3000 psi, are amply strong for our use. There are a lot of handy fittings that make tight quarters plumbing jobs easier as well, such as swivels, male elbows, etc.

- Bart
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