rust!

50 PSI ?

Is there a name plate ?

I do not have a wood boiler, yet... But I used to work in a really old paper mill, and we would see a lot of flange like this. And as the mainteance budget was always busted, we would put a new gasket and just like you said, add washers as spacer to get everything tight, and on e everything was tight, it would hold for a while. I would think that is you can get a new gasket and pass the 60 psi pressure test you would be fine . ( if the manual recommand 60 psi, I would not push my luck at 72 psi )

The same happened to me with an oil fired furnace with domestic hot water supply. Once I replaced the core, I use to put white lithium grease on the bolts.

Most of the time your system should not see anything over 25 PSI or steam temperatures , so be content that It won't leak at this pressure . If you want the higher pressures do the proper repair job NOW!

if you have 30 psi safety valve, then I would recommend you only test 30 x 1.5 = 45 psi.
The working pressure will be between 10 and 15 psi, correct?

10 yrs navy nuclear power, 15 yrs trash to energy power plant, we have stuff up to 1200 psi at work.

Maybe it is just rust & scale build up, but that flange face / surface looks nasty. I would try to clean that up really good. A lot of "tapping" with a cold chisel, wire brush, etc. If you have a compressor, get a small "needle gun" or "needle scaler" from Harbor Freight for < 20 bucks and be done in 5 minutes or less.

Are those studs firmly attached (welded in) or do they just thread into the flange? If they thread in, after everything is cleaned up well, soak them liberally with the best penetrating oil you can find, install 2 nuts on the end, heat the FLANGE area (not the stud) with a torch (propane, mapp gas, or acelyene). This will allow the flange to expand away from the stud threads and help break the corrosion bond. Then remove the stud via "double nutting".

As far as pressure testing.....sometimes equipment will have a set pressure rating, and be tested to 1.5 or 2 times that for a static test. Sometimes items are proof tested ONCE to something higher. I.E. rated for 30, designed for 60 max, proof tested to 72. I would not routinely pressurize up to that maximum, especially with cheap, homeowner grade pressure gauges because they can be off as much as 25% of full scale.

For example, our steam plant at work is a 1200 psi system. The boilers routinely run 980 - 1000 psi at 830 deg F. After any breach, patches, tube or valve repairs or replacements, etc, we refill the system (13,000 gal per boiler) with cold (50-70 deg) demineralized water, then slowly pressurize with the feed water pump up to 840. You do not go to full rated pressure when cold due to brittle fracture concerns.

Like others said, I would just test to about 50 psi and call it a day.

Once the area is cleaned, you may be able to tell if the studs are threaded in or welded. If they are threaded, the threads may be sealed with a pipe dope type of goop.

Have you thought of cutting the studs off flush with the flange, drilling them out, threading the hole, installing studs / bolts and sealing the threads with pipe dope?

Those studs look plenty beefy to hold 30+ psi. What are they, about 3/8" or better? That kind of 4 bolt flange will hold hundreds of pounds of pressure.

Carl Webber said:

This is awesome. You have some good information. Just to be clear, are you telling me that i should not test my boiler to 72psi like the tag says? I know that normal pressure relief valves for a boiler release at 30 psi. Should i only test to about 40 or 50psi? That way i have exceeded the maximum that the boiler should have to handle under normal operating conditions but i haven't gone too far. I would hate to blow up my boiler by pressure testing it.

I do agree that everything needs cleaning. I was hoping to clean it up before putting everything back together but i put pictures on here first because it wouldn't make sense for me to clean it up if i was going to have to replace the flange and have a new one welded one.

With this much corrosion how do i tell weather the studs are threaded in or welded? It would be really beneficial to me if they were threaded in as i could just remove them and put in new ones instead of hiring someone to do some welding for me. I'm not sure but i think they are welded because there is a gap between the back side of the flange and the plate steel the boiler is made of. If the studs were threaded in wouldn't they leak?

If the studs are welded on, can i just have someone come tack some new ones on or do i need to have the whole flange replaced with a new flange with the studs already welded in it? I guess really what i want to know is if i have someone tack weld some new studs on will they hold with the heat and pressure or do i need to replace the whole flange to accomplish that?

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My suggestion would be a 30 psi test.
Clean the flanges and make some thick fiber gaskets with material from an auto parts. A good high temperature gasket sealer like Permatex2

You can get deep nuts like the use to connect all thread threaded rod. That would take advantage of all the thread you have

But replacing the threads would be better yet

I'm 100% with Bob. The boiler already passed 3x the normal working pressure, so I think you're done pressure testing. Thick gasket and high-temp silicone goop should do the trick. We're not talking super high pressures or temps here.

I purchased an OT-50 in the Fall of 1978 - it was one of the ones on the first container load of HS Tarm boilers imported into the US from Denmark. It is a great boiler, none better. I have burned hundreds of cords of wood in it over the time I have used it along with less than 500 gallons of oil to heat my home. Don't let anyone try to get you to replace it - it is very durable and will last for many years. The OT-50's virtues are many, but chief among them is its size. Unlike the newer wood-fired boilers, it holds a massive amount of water, enough so that one could get by without using external thermal storage, although any form of external storage able to handle the fluctuating pressure of boiler water is never a bad idea. The newer boilers require some sort of an external storage tank because these new boilers hold so little water by comparison, usually less than 40 gallons. The other big virtue of the OT boilers(OT-28, 35, 50 and 70) is that they can operate without electricity and can utilize gravity circulation provided the boiler is located below the hydronic baseboard/radiators, enabling one to heat throughout even an extended power outage. The newer boilers, efficient as they are, require a somewhat significant amount of AC to work and run. The weak points of the OT-50 are ones shared by all boilers, especially wood-fired boilers, namely leaks around the flanges and seals that begin to appear over time. Worst among them(the OT-50's chief trouble spot) is the 4 bolt flange(supply and return) on the back of the boiler, pictures of which Carl Webber has here on display above. The 4 bolt hole gasket that seals this flange eventually hardens and becomes brittle over time, made especially so by the all-to-frequent changes in boiler water temperature. I have replaced these gaskets several times over the last 38 years and I have yet to find a gasket material that stands up to the stress of these changes in boiler water temps. The upper flange is the one most susceptible to this problem because the range of temperature variation is more extreme here than with the return port. When a new generation of MB-Solo boilers appeared in the 1980s, Tarm replaced these 4 bolt hole flanges with FPT fittings welded to the boiler, much like the other fittings already there on the back and the top of the boiler. A good welder could retrofit an OT-50 with these fittings, and I must say I have been tempted to do so, but it's not as easy as it sounds when one looks at how Tarm fabricated this part of their OT boilers. If you do replace the flange gaskets, it might be a good idea to use a liberal amount of Permatex Ultra-Blue RTV sealant on both sides of the gasket, provided the gasket material you have chosen is not adversely affected by RTV Silicone. I would also use a torque wrench to tighten down the four 19mm nuts that hold the flange to the boiler. And I would also use an anti-seize thread compound on the threads to keep them limber for future repair. The last thing you want to do is to snap off one of those 19mm studs welded to the back of the boiler while trying to loosen the nuts.
The other place to look for leaks is where the domestic hot water coil or tank lid is bolted to the top surface of the boiler in-between which a gigantic O ring is used to seal the connection. I have used Permatex Ultra Blue sealant on both sides of this seal to try and stop leaks in this area of the boiler. And I have also used anti-seize on these threaded studs and have torqued down the lid carefully(15 foot pounds). This seems to have worked well over time during which the big O-Ring deteriorates and loses its flexibility.
If you use the 4 port mixing valve that you could have bought with the boiler way back when(highly recommended), then you have probably noticed the leaks that often occur around the shaft that goes into the valve. It is sealed on the inside and the outside of the valve with two small O-Rings. Mine started to leak rather soon after installation. I believe Tarm did not choose the right O ring for this task. I would replace them with a BUNA type O ring, Size 111, available from McMaster-Carr or some other sources as well in packs of 100. You will have plenty of spares. And I would use a silicone grease or a grease that can be used in marine environments on the shaft in-between the O-rings. Buna O-rings are resistant to hot water and grease and tolerate the wear and tear that comes from the frequent movement of the mixing valve shaft. The 4 port mixing valve could have come as a part of an assembly that includes the two flanges or separately, and it could be operated either manually or with an Amimat controller electrically controlled from a thermostat.

The newer boilers, efficient as they are, require a somewhat significant amount of AC to work and run.

Not all of them.

I went thru these gasket issues too on my old wood/oil combo unit, where the DHW coils bolted into the back. I had the thing 17 years, they were replaced once by a service guy, and I did them once. They were likely almost due for new ones when I got rid of it. Pretty frustrating. When I did them, I put a thin layer of grease on them. Have no idea of that was a good or bad thing to do. But the old ones were pretty well cooked.

On the flanges above, I was going to say maybe just bolt the flanges in place, then get them welded there. But looking at the top pics, that looks like a pretty difficult task - that orange metal doesn't look removeable? I thought when the thread first came up the orange was boiler skins - but now looking at it again, doesn't look like that. But if so, I think I would try welding.

Not familiar with Tarm, but most of those flanges are standard pipe sizes. I used to see very similar in Chromalox Electric hot water boilers. First get the old gaskets off and you will find that the bolts are a standard size that fit thru the four holes. (5/8 in our case) We used to get gaskets either from Chromalox or any plumbing wholesaler. Grease well with NeverSeize when you are putting things back together.
Any time we had any welding done we were supposed to use a licensed weldor and get the boiler inspector involved...