Calculating make-up torque for manufactured buttress connection

[CDN2015]

Hi All,
I would like to know how the make-up torque for a buttress connection is calculated. I know there are values in different books but I would like to calculate the required make-up torque as we have designed special crossovers from bar stocks which are of higher grade / tensile strength than the regular N-80 casing.

 

[desertfox]

Hi

I would like to help but I don't understand what you mean by "special crossovers"? Nor do I understand what you mean by "make up torque" and apart from the fact there are no material grades specified from which you have manufactured any of the components your asking about, how would you help someone given this information?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[CDN2015]

Desertfox,
So sorry, about the lack of information to make a decision. Basically the crossover is from 9-5/8" to 7". It was made from 4145 steel bar stock. Internal 7" buttress box connection was machined so as to be able to make-up a 7" landing string inside it. The make-up torque I request is the standard ft-Ibs required to properly makeup the casing string to the crossover. I know to properly make-up Buttress connection is making it up to the base of the triangle up to the apex of the triangle on the connection but the problem is we had to use a very high torque to break it out at the jobsite. The 7" casing is N-80 which has a lower tensile and yield strength than the bar stock used to make the crossover. That is why I would like to know the formula used to calculate the required make-up torque based on the different material types planned to be made-up together.
I have attached a little schematic to help understand the issue.

 

[desertfox]

Hi CDN2015

I think I understand a little now, your question relates to oil drilling equipment which I know very little about but from what I've googled the casings are screwed together and form a sleeve for a drill to pass through during drilling operations for oil or gas, is that correct?

Now do you have any information regarding the axial force and torque these devices are subjected to, I'm assuming that these joints are similar to conventional bolted joints where we torque up the bolts to a suitable preload in excess of the external forces imposed on them.
Now sadly torque is not a very accurate way to make a sound joint mainly because of friction on the threads has you alluded to in first post.

Are you simply looking to achieve the maximum static torque which can be sustained with your on the components you mention.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[desertfox]

Hi
I found a couple of sites this one is a calculator for buttress threads

http://www.oilzonetools.com/buttress_thread_strength.html

This next link is torque based on API

http://www.scribd.com/mobile/doc/87734864/API-Thread-Torque-Table

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[yudhichen]

According to API RP 5C1 18th edition, the make-up torque for buttress connection was based on triangle mark.
API doesn't specify torque value for buttress during that time.

this is just my opinion, API mention that way due to the nature of buttress sealing.
buttress thread sealing located at interference of thread flank. The only way to ensure buttress sealing is
by triangle mark to ensure each thread flank has interefere each other as the first quality assurance method.
once the first joint was made, then next acceptance criteria being change into torque value.

Currently, I also heard another API standard which mention buttress torque in API TR5 TP 1st edition.
perhaps you might look more information from there.