Nozzle reinforcement pad thickness requirement 2

[darrenyee88]

Hi,

I read in a Pressure vessel design manual and found out that the book states that

"Thickness.
While minimum thicknesses are given in Reference 1,
Section UG-IG(b), it is recommended that pads be not
less than 75% nor more than 150% of the part to which
they are attached."

I am just curious of the reasons behind it. Is it that if the reinforcement pad thickess is higher than the shell thickness, more stress will be on the shell ? What will happen if the thickness of the reinforcement is thinner than the shell thickness.

 

[Duwe6]

Greatly thicker concentrates the loadings more than a nominal one.
Greatly thinner may have its perimeter so far out that is does not take up all of the nozz loadings. Remember ASME VIII Div-1 is "design by cookbook" and uses a lot of 'rules of thumb'.

 

[MJCronin]

The consensus opinion is that the 75-150% limitations are the "sweet spot" for design.

If the pad is too thin and large it will be awkward, expensive and unsuitable for high temperature installations (as the vessel thermally expands, high local pad stresses will be developed)

If the pad is too small and too thick, it will present a "hard spot" that will cause high stresses as the vessel is pressurized

http://www.eng-tips.com/viewthread.cfm?qid=176764

http://www.eng-tips.com/viewthread.cfm?qid=201779

http://books.google.com/books?id=m6...forcement "hard spot" pressure vessel&f=false

MJCronin
Sr. Process Engineer

 

[darrenyee88]

Thanks alot. MJCronin , the links provided by you will useful.