support saddle recuperator duct

[Didier19]

hello everyone i am new here and this is my first topic

i'm a QC supervisor and we have a problem with some saddle support for a heat recuperator duct with 4100 mm Diameter,
the main problem is the saddle are no in 100% contact with the duct , they have a gap like 5-7 mm, in a 70% of the saddle lenght but i need to support with a code or specification that saddle need to be in touch in the 100% of the section. the fabricacion of the duct was in italy but installed in mexico.

the duct is only for air, and they only support his own weight, i am not sure if 100% is necessary, actually it in contact in the edge saddles

 

[1503-44]

Difficult to see what is going on there, other than that there is some kind of gap somewhere. Too much detail to determine anything that might have global implications. Are you missing 7mm in a run of 4100? I doubt it is required for strength, but who knows.

No pipe code I know applies to ducting.

If you are the inspector, you should have a copy of the actual fabrication specification, including references to any codes that apply, that were used to construct that assembly and the drawings showing the weld details, type and other requirements. Otherwise all you can do is flag the item, note the question or deficiency and raise an engineering/construction query for resolution by others.



“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[saplanti]

Didier19,
Under this condition the duct load will be at the both ends of the saddle. The saddle will be under tension as well as bending moment. In case the saddle was designed for these actions there will be no problem for the saddle.

If you heard of Zıck’s analysis of ducts or vessel on saddle, the highest stresses on the duct are around the saddie edges on the duct sides. But this analysis require full contact between the duct and the saddle. In your case these stresses are going to be a lot higher and probably duct will go to plastic deformation if the duct was designed for this action.

The best is to report the problem to get the designer’s attention and answer.