The Steamboating Forum

Hi all,

Knowing that stainless steel is not being accepted in Anglo-Saxon countries for the manufacturing of heated pressure vessels, I thought it would be interesting for you to know that stainless boilers can get the necessary certification in Europe, provided a series of requirements are satisfied. As far as I know, several boats with stainless boilers are being operated in Germany, and at least one in France.

I started the process by preparing a sketch with the desired layout. My initial strength calculations had to be confirmed, and the final drawings made by a specialist prior to submiting the project for approval.

By trying to save the inner and outer boiler hoods of a previous boiler, I shooted myself in the foot... Otherwise, the boiler could have had a larger heating surface.

The work was carried out in a certified workshop, the process being supervised by the TÜV (German Technical Inspection Agency).

Here is the sketch of the desired layout:




Cut to length and prepared for welding: 151 tubes 25 x 1.5 mm




One of the two tube plates, laser cut, waiting to be bevelled:




Components put together:




Ready for welding:



The shell, laser cut, rolled and welded:

Part 2

Tube assembly and outer shell, ready for welding:



The certified TIG welder in action:




The result of a time-consuming work:



The boiler during the final inspection and acceptance test:



Following the rigorous requirements: cold pressure test to 30 bar



Acceptance test passed, TÜV-issued certificate:




See Part 3

Part 3


Being a dry fire box boiler, no certification is required for the fire box which can be welded in a different workshop. The box is my own design.

Fire box as it came from the workshop:




Hardening the refractory insulation:



Pressure vessel and fire box after assembly. Mahogany cladding.



Full equipped and installed on board:




Albert

Yes, looking at that tube plate; aren't CNC laser cutters wonderful?
151 tube holes to drill and ream . . . . . no thanks!

That's a thing of beauty. If its TUV certified that's more than enough to tell me it is safe, so why doesn't the ASME accept it?

Regarding the laser cut holes, having read others build threads where they manually drilled the holes...it just doesn't make sense to me when laser cutting is available. There is certainly something to be said for making something yourself, but laser cutting is cheap compared to the time you would spend doing it.

SailorHarry wrote:Regarding the laser cut holes, having read others build threads where they manually drilled the holes...it just doesn't make sense to me when laser cutting is available. There is certainly something to be said for making something yourself, but laser cutting is cheap compared to the time you would spend doing it.

There's also the time taken to just mark it out accurately! The laser would be half way done already.

SailorHarry wrote:... Regarding the laser cut holes, having read others build threads where they manually drilled the holes...it just doesn't make sense to me when laser cutting is available. There is certainly something to be said for making something yourself, but laser cutting is cheap compared to the time you would spend doing it.

In our shop, we have had the third-party laser cutter botch some large tube sheet jobs. Hours were spent dressing the cuts and gouges with welding. So, like many things, it is not a panacea. On some things, laser cutting has worked flawlessly, but on Saturday I finished boring my launch boiler tube sheets the old fashioned way: centering bit followed by drill followed by reamer.

Albert, I am curious as to the permitted stainless materials for a steam boiler under the rules to which your boiler is built, do you have this information?

"If its TUV certified that's more than enough to tell me it is safe, so why doesn't the ASME accept it?" The ASME Code does not permit most stainless steels for boiler service because of the innergranular chloride stress corrosion issues. The most common stainless steels (300 Series, 304, 316, etc. in the ASME-ASTM Specifications) are not permitted unless water quality is held to very strict limits, which is orders of magnitude lower chlorides than we can obtain in our steamboats.

Some grades of stainless are permitted in the ASME Code (martensitic stainless) , and I understand that the Duplex materials have had some approvals exterior to the ASME Code jurisdiction, and perhaps Duplex steels may be allowed at some future date.

Hi Fred,

The stainless material for my boiler is a so called austenitic steel, material number 1.4571 ( X 6 CrNiMoTi 17 122). Which range of stainless materials is being otherwise permitted for this application is beyond my knowledge.

Albert

Fred, the submitted drawings include a temperature limitation at the top tube plate to 400 °C (752 °F).

For this limit temperature, the material table for 1.4571 includes a note: "When used up to this limit temperature, no intercrystalline corrosion occurs during an operating time of up to 100,000 hours" (Test acc. to DIN 50914).

Albert