ASME Section IV Heating Boiler - Ligament Efficiency

[bithack]

Section IV states maximum pitch dimensions for tube sheets stayed with fire tubes. What calculation determines the minimum ligament distance between tube holes? Are there minimum ligament efficiency percentages that guard against tube holes placed to close to each other.

 

[GenB]

Exactly. ligamentefficiency calculation is needed. Ifyou place the tubeholes closer. Your pressre will diminish. And if you place them too far apart too.

 

[bithack]

Not sure I understand your response to my question?

What "calculation" determines whether or not you have a ligament that is too small?

Thanks.

 

[Fizza453]

I am sure ligament width is not specified in Section IV and not in Section I.
You can keep as much small as praticable as far as Code is concerned.
If tubesheet thickness is adequate against ligament width, then you can keep any minimum.
TEMA has guidelines on minimum ligament widths.
Keep in consideration the weld fillet size (if tubes are welded) while deciding the minimum ligament width.
If tubes are flared, then you need more ligament width.


Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[bithack]

Thanks for the reply. ... What limits a design from potential heat stress fractures between tubes. What is the purpose of ligament efficiency per Section IV??