Hi Doug,

I have been working to improve my understanding and calculations relating to the strength of boilers.

There seems to be a big gap in the papers I have researched that no-one has checked things like flue tubes in compression, yet the way they are situated in boilers means they must be calculated as a significant part of the boiler. (e.g. a compressive collapse of a tube would be likely to be catastrophic, as the end silver soldering would be expected to fail and the boiler eject its contents very rapidly!).

I have de-rated the "Permissible compressive stress" - following the ASME rules, plus converting the "ASME Permissible tensile stress" to "Permissible compressive stress" by the factor of:

__Comp. stress __ = __ 45 __(MPa) = 0.214

UTS at room temp. 210 (MPa)

So Here's my calculations on your flue tubes:

At 70psig:

σc = [(14.7 x 0.252 – 84.7 x 0.282) / (0.282 - 0.252 )] - [ 0.252 x 0.282 x (84.7 – 14.7) / { 0.252 ( 0.282 - 0.252 )}] :

σc = [(14.7 x 0.0625 – 84.7 x 0.0784) / (0.0159)] - [ 0.0625 x 0.0784 x (84.7 – 14.7) / { 0.0625 ( 0.0159)}] :

σc = [(0.9188 – 6.640) / (0.0159)] - [ 0.0625 x 0.0784 x (70) / { 0.0009937)}] :

σc = [(– 5.72) / (0.0159)] - [ 0.343 / 0.0009937] :

σc = [-360] - [ 345.2] = -705.2 psi:

This is less than the 767psi limit for copper at the temperature for NWP = 70psig.

I.E. __The flue tubes are acceptable for NWP = 70psig.__

This supercedes my post of #82, so if you need the correct calcs, please do not use post #82.

I understand you have rated your boiler at 50psig NWP., so it is OK.

Regards,

K2