Boiler questions

[Jack Innes]

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Thank you again. I will run the safety valve discharge vertically & at the same size as the outlet - 3/4" if I use the existing valve.

I am concerned about the safety valve not being on its own boiler penetration. This boiler has only one outlet on the steam dome, that being 3/8" npt. I have checked the entire upper surface with a tiny video camera & there is definitely no other outlet on top of the boiler. The picture shows the setup with what I referred to as a manifold - it is actually a 6 outlet steel tee type of fitting with the safety valve on the top outlet. The fitting is connected to the steam dome by two nipples & a union. It will be a little closer once tightened. It needs to be spaced as shown to clear the stack base. The throttle, whistle & gauge feed of three of the remaining outlets. The loose end will have a support attached connecting it to the boiler. What can be done about the lack of a dedicated outlet for the safety valve?

Jack

[Lopez Mike]

I would go buy a weldolet (sp?) Fred, somebody? Is that right?

Have a competent welder with experience on pressure vessels install it. While you are at it, I would add several. Plug the ones you don't use right away. Believe me, there are seldom enough of the things. My boiler has about twice as many as I use. It is so nice to have them and I don't believe that it weakens the boiler. Stop and calculate.

A 1/2" weldolet fitting requires perhaps a one inch hole max. That has an area of about .8 square inches. At a hydro test of, say 250 psi that is a load of 200 lbs. A strong person can pull that hard.

I don't know what your boiler designer/builder was thinking of to A: put the safety on a manifold and B: not provide extra penetrations. The same dolt who built my boat perhaps. Sigh.

This is your chance to add fittings in the right place for whatever else you might add in the future. Each feedwater method on its own penetration, for instance.

Mike

[johnp]

Hey Jack, Check you PM's

[fredrosse]

I would go buy a weldolet (sp?) Fred, somebody? Is that right?

A heavy steel forging for welding onto a pressure vessel is named a "Thread-o-let" or a "Weld-o-let" The threadolet is what we use, it has female pipe threads for screwing on piping. A weldolet is similar, but it has no threads, just a socket to insert pipe, which is then welded in place.

[Lopez Mike]

I knew I'd get it wrong or at least not quite right.

To be honest, I have bought a lot of Schedule 80 female to female couplers, cut them in half and used them with no repercussions beyond some shuddering from a couple of friends. Just make sure you bevel them for full penetration as per proper welding practice.

Mike

[fredrosse]

" Schedule 80 female to female couplers, cut them in half and used them with no repercussions beyond some shuddering from a couple of friends"

If you want to do it according to code, use a-105 Thread-o-lets. If you are building (or repairing) a non-code boiler, schedule 80 female couplings cut in half (or "half-couplings" as they are sold already short) are OK for many applications. The short "half couplings" are to be used to attach connections to atmospheric tanks etc.

As Mike stated: An important part of this is to have "full penetration" welds between the thread-o-let, (or the coupling) and the pressure vessel. That is done by having a bevel machined or ground on the welding surface, about 45 degrees. AND having the connection held about 1/8 inch away from the pressure vessel before welding. This gap is required. If welding rods more than 1/8 inch diameter are used, then the gap should be at least as much as the welding rod diameter.

Do not use MIG to put a pressure vessel or its connections together , stick welding is the way to go, unless you have fancy welding equipment that would be found in a pressure vessel factory or similar.

[DetroiTug]

The thread-o-lets are very inexpensive too compared to everything else "steam boiler". A 1/2" high pressure thread-o-let is like five bucks. Not worth messing around with anything else.

-Ron

[Lopez Mike]

I agree on the Thread-o-lets being a better choice. I suggest the Schedule 80 stuff just because it can sometimes be hard to find the right thing when you live in the sticks. I've cleaned out the local 'old time' hardware store more than once just finding Sched. 80 nipples. And that is in a small industrial fishing town.

It is worth the time and money to have a certified pressure vessel welder do the work and ask to watch for a while. I tack things together for convenience and then have all the rest done by an expert.

First thing is, as Fred says, is the bevel and the spacing. Then, what they call the 'root weld' is done with TiG. All weld starting and stopping points are ground clean so that there are no inclusions and, in the case of a long weld going around a large cylinder like a firetube boiler shell, the weld is done in short segments spaced equally around the circumference. After the root weld is done, out comes the 7018 rod. Same thing about grinding out the starts and stops and doing it in equally spaced segments.

When it's all done, you realize what a bargain it is, especially when you hydro test and steam up for the first few times. Peace of mind is priceless.

Mike

[johnp]

I couldn't find thread-o-lets nearby at the time so i ended up making my own on the lathe from solid bar. I beveled them made them slip into the tank a bit and welded them with the mig using fluxcore wire. I hope it's ok, it,s been 2 years and a few hydro tests to 175psi. Safety is at 125 and i normally run at 75-80.

[Lopez Mike]

Obviously it's working and I think it's probably safe. We tend to recommend doing things by the book on here out a fear that there will be an accident or failure and then we would be asking ourselves if we gave poor advice.

On a penetration, the highest loads are more likely to be bending forces rather than pressure. That's why our N.W. Steam Society specifies Schedule 80 nipples between a boiler penetration and the shutoff valve. Also, no close nipples. Too weak in bending.

Mike