Super Heater Testing

[sbwhart]

At what point do you test a super heater and how.

Does the 4 yearly 1 1/2 working pressure test require any testing of the super heater if so how or is it just a visual inspection?.

Stew

[John Baguley]

Hi Stew,

The Green Book recommends that the superheaters are given a twice working pressure test before fitting to the boiler but it is only a recommendation. It's probably easier to test the superheater when it is fitted to the boiler and the boiler is having it's 1.5 times working pressure test, by blanking off the steam connection/s to the cylinders. That also helps if the regulator leaks a bit under hydraulic pressure as the test is done with the regulator open.

The superheaters should be tested at the four yearly test IF PRACTICAL. It's not compulsory.

John

[sbwhart]

Hi John

Thanks for your reply.

That's my understanding also, having checked the green book.

It would be interesting to know if any one has experienced a supper heater failure whilst in steam.

Cheers
Stew

[pault]

I have seen a number of superheater failures on 7 ¼” gauge locos and without exception they have been unspectacular. They have generally been found as a result of investigations into poor steaming or very excessive water consumption, rather than a realisation that an element has failed.

[doubletop]

Isn't it dependent upon whether they are before or after the regulator? If they are after the regulator they are only subject to valve chest pressure, which is unlikley to be full boiler pressure for extended periods, if ever. If they are before the regulator ther are always subject to full boiler pressure and therefore an integral part of the boiler need to be part of the boiler test.

If the regulator is located in the smokebox the superheaters are most likely before the regulator, if the regulator is in the dome then they are most likely after it.

We've recently had a failure, of a superheater on 7.25" loco which was before the regulator. The problem was the silver soldered transistion from copper to stainless tube, although a feature of a number of well known designs it is apperenly not recommenetd as the joint can fail, particulalry when subject to full boiler pressure. In this case the owners has replaced with a fully stainless set of superheaters which have been tig welded. Failure wasn't spectacular, and not noticed for a long while, only when preformance dropped off.

But I'm not an expert......

Pete

[steam4ian]

By my personal experience superheater failures, particularly if after the regulator, are singularly unspectacular.

I am presently stripping my loco because a hole about 5mm diameter blew out of my header. I was aware for a few weeks preceding taking the loco out of service that when going through the tunnel I could hear a steam leak, it was inaudible otherwise. On the last steaming day I could hear a blow in the smoke box even when not in the tunnel. I continued steaming all afternoon even though I expected to fail at any time; the loco never faltered and in fact steamed very well.

The superheater element are SS radiant type but the header appears to be a length of brass plumbing nipple; not a great choice of materials.

[runner42]

Aug 6, 2017 6:00:33 GMT steam4ian said:

By my personal experience superheater failures, particularly if after the regulator, are singularly unspectacular.

I am presently stripping my loco because a hole about 5mm diameter blew out of my header. I was aware for a few weeks preceding taking the loco out of service that when going through the tunnel I could hear a steam leak, it was inaudible otherwise. On the last steaming day I could hear a blow in the smoke box even when not in the tunnel. I continued steaming all afternoon even though I expected to fail at any time; the loco never faltered and in fact steamed very well.

The superheater element are SS radiant type but the header appears to be a length of brass plumbing nipple; not a great choice of materials.

Hi Ian,

I just stumbled on your post, I am a slow reader. Yesterday Allan Wallace showed me a header that had recently failed, he said that the header made from copper tube didn't have the same ability to withstand high temperatures as brass, which he was using to make the replacement header. So maybe your header was the right material and others factors such as material thickness was the cause of failure.

Brian

[steam4ian]

G'day Brian

I haven't been on here for a while so missed your response. Too much work to do getting the property bush-fire ready.

Thanks for the heads up, I will contact Allan for a discussion on materials.

All the best for Christmas and the New Year

Regards
Ian

[smallbrother]

I had a failure in September with my Holmside 7.25". It had recently passed the hydraulic test too. The super-heater is of course sited after the regulator.

The 2 radiant elements were made of copper it turned out and one had a hole about 3mm diameter. She wouldn't hold steam on a run and I was getting blow-back through the fire when opening the regulator. There was no convenient joint in the smokebox to facilitate removal.

After some wrestling and hack-sawing we got the assembly out of the boiler. I took it to a pro model engineer and the repair was made to the stainless steel part of the super-heater so it now shorter and has no radiant elements. The header was reduced too so it all slides easily in and out. The pipework from the header now has an easy to get at joint.

She seems to be ok with this, but I have only managed some brief runs since the repair so not entirely sure as yet.

I now understand (a) copper is useless as a radiant element material and (b) to make the super-heater easy to remove.

Always learning!

Pete.

[Shawki Shlemon]

When I test/retest my boilers , I blank the S. H outlets to cylinders and open the regulator , this ensure the S.H is OK and also overcome problems of leaky regulators .