【转帖】erminology on mechanical drawing

yang686526

terminology on mechanical drawing
this is probably a simple question but google and my colleagues haven't been much help so far:
a fairly large vessel, almost certainly clad with thermal insulation, has two dimensions shown for its diameter: one is a plain 13.8m, the other is slightly larger "15.9m t/t". what does the t/t suffix signify? the two dimensions clearly aren't i.d. and o.d. so i'm wondering if it is diameter over the thermal insulation, or the dimension or between ports? or something else entirely? would appreciate if someone could help me out!
   
----------------------------------
  
if we learn from our mistakes i'm getting a great education!

eng-tips forums is member supported.
this "t/t" is no way appears to be meaningful communication.  if non-standard terms are used on drawings, they either need to be defined in the notes or in the company standard which can be made available to anyone reading the drawing.  in this case, instead of using "t/t", i would've use a delta note and explained what i meant in the general notes with full verbage.  
sorry i couldn't help on this though.  do you have an example of this you can post so maybe we can through some guesses at you?
matt lorono
cad engineer/ecn analyst
silicon valley, ca
scotty, there if you don't get the answer you need here, maybe over in
standard vessel terminology:
t/t = "tangent-to-tangent".
this is the length of the straight side from one tangent line to the other tangent line.

guyss,
thank you all very much.
   
----------------------------------
  
if we learn from our mistakes i'm getting a great education!

i concur that pennpiper gave you the right answer.
it means "tangent to tangent" or the straight length of the vessel including the straight flange portions of the curved vessel heads.