Requirement of notch in elbow lug

[lilsam]

I am looking for a reference or an explanation on the requirements on notch in elbow lug. Some project support standards require it and some not. Please anyone who has an explanation on this, kindly help me.

Is it concern with the stress on the elbow during expansion? What happens if there is no notch on this lug?

 

[JohnBreen]

Hello lilsam,

Presumably you are referring to the notches at the weld line where the lug, trunnion or plate is attached by welding to the OD (extrados) of the elbow or bend. The purpose of these notches is to ameliorate the effect of the lug or plate "lagging behind" in heat transfer during heat-up and cool-down (e.g., the appurtenance will "lag" and be cooler than the pipe on heat-up). The welded appurtenance usually extends beyond the pipe insulation and it is effectively a "heat sink". If the weld that attaches the welded appurtenance to the extrados of the elbow were to be continuous there would be a shear line (stress) along the weld. Often you will see a notch with a round hole at the end away from the weld. This round opening is intended to act as a "crack arrestor" to prevent fatigue cracks (due to cyclic temperature excursions). These weldments are intended for high temperature pipe and are often ignored for piping that will not exceed about 400 degrees F.

The B31.1 Code provides reference to Pipe Fabrication Institute publication ES-26, in which the methods of fabricating welded appurtenances of this type are detailed.

Regards, John.

 

[lilsam]

Hi John,

Thank you for this info. definitely it help a lot.

Thanks...

Cheers...