Size of weld required on Weld-o-Letts

[miked7]

WOLs come in set scheds. Often we are setting wols on thin pipe and do not want to weld all wol prep out as it is not cost effective and causes distortion of carrier pipe. Anybody know of specification or "rule of thumb" for minimum amount of weld required on wol for given carrier or tak-off pipe sched/Wall thickness or strength?

 

[deanc]

The throat size is equal to the thickness of the thinner material. You must also satisfy the requirements of the construction code,ie:shear and loads.

 

[DSB123]

deanc,
Your answer is incorrect. To only apply weld to the thickness of the thinner material is dangerous and not in compliance with the fitting manufacturers requirements.

This is a good question. On many occasions in the past I have come across Weldolets which have not been fully welded out to the weld line. One in particular resulted in a near catastrophic failure. In general I find that contractors do not fully weld out weldolets to the weld line generally with the mis-conception that provided they have the same thickness as the branch wall they will be O.K. However what they forget to understand is that in many situations Weldolets have been specified to meet Thermal Stress Analysis requirements and not just Pressure reinforcement. As such "Code" stress intensification factors have been used to calculate the stress levels. These "Code" SIF's are lower than set-on branch SIF's since they are based upon the assumption that the Weldolet is fully welded out to the weld line. In not fully welding out the Weldolet then the actual SIF's are far greater than the "Code" values. The problem is that in many cases the Pipe Stress Engineer has assumed that the Weldolet is fully welded out whereas in fact the inspector approves cases where this has not occurred. This is a recipe for disaster. Weldolets which are not fully welded out in my opinion are worse than Set-on branches due to the inherent "Notch" that is in-built in the fabrication. I have even come across Weldolets specified for a 20"nb branch on a 40"nb line. Again these were not welded out fully, to the extent that shart "notches" were formed, and the Pipe Stress engineer had assumed the "Code" SIF's in his analysis.Scary!!!. My opinion is that Weldolets should be fully welded out always and if the parent pipe is so thin that distortion is a problem then use some other type of fitting.

miked7,
Please have a look at Thread378-22947 for a better understanding of the welding requirements for Weldolets if you want to avoid failures.

 

[deanc]

Very well DSB123,I consider myself corrected and chastised.

One does need to follow the requirements of the fitting Manuf. As is pointed out in several Code Interpretations.

Perhaps a weld-o-let is not appropriate for this application.

Beware of what you read here! These are all only opinions.

 

[miked7]

Thank you Deanc and DSB123 for you comments. Myself, for what it is worth, feel that you are both right and have valied views. I have never found any specific guidance from codes. Some Clients (eg. Shell) put riders into their DEPs instructing filling W-O-Ls out completely. I have always tried to get acceptance that W-O-Ls should have weld throat thickness of 1.5 x WT of the take-off pipe. However this is a WAG (wild ass guess) as there is no firm engineering basis for this. As for the stress notch effect that DSB123 advises, I can only agree.
Regards. MD