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API and Non-API Casings and connections
22 September 2020
Are all Non API threadings considered as Premium Connections. Whether Buttress Threading Connection on a 14" L-80 grade pipe is API/Non-API/Premium Connection?
6 answer(s)
Drillling Engineer
Pakistan Petroleum Ltd
Total Posts: 5
Join Date: 03/08/19
I concur with Umair Baig comment. It's non API connection. Compatibility issues might arise with different vendors of casing having same size of BTC connection. The reason is their extrapolation method that might differ for making it's physical properties more nearer to API BTC connection.
Drilling Engineering and Planning Director
Total Posts: 12
Join Date: 13/02/12
BTC connection is part of API 5CT so it’s considered as API connexion and free to cut because there no royalty to pay.

The denomination Premium indicated that the connection is more sophisticated than API thread but nothing much.

There is a bunch of premium connections that have different design and performance. That’s the reason the norm ISO 13679:2019 “Petroleum and natural gas industries — Procedures for testing casing and tubing connections” is giving more clarity about how to test and qualify connexion according to a certain number of criteria. The norm précise four categories called CAL I, II, III and IV. The higher the number, the more sophisticated is the test, for example CAL IV connection is tested with gas in all the areas of Von Misses ellipse (four quadrants) plus temperature and bending.

Moreover the qualification cannot be given to a connection but you have to associate its grade and thickness and a full ISO test costs a lot of money and so casing manufacturer test only widely used casing diameters. Just as an exemple for 7" 29# P110, VAM TOP is CAL III and VAM 21 is CAL IV.

Some companies have their own testing procedures but most of the rest utilise the ISO 13679. This norm has made more clarity about the premium term which is rather commercial than technical.

Finally, I think that if your 14" L80 BTC connexion would be tested it would be qualified CAL I only.

Managing director Punch Energy Services
Punch Energy Services
Total Posts: 18
Join Date: 24/06/20
Hello Dan,

Good input but please note that the premium connections you are listing are drill pipe connections.
In my view the discussion (question) was tubular (casing / tubing) connection related.

Best regards,

Workover Engineer
SPREAD Associates
Total Posts: 21
Join Date: 01/08/18

Joint efficiency is defined as a ratio of joint tensile strength to pipe body tensile strength.

The connection strength of premium connection is high and can be equal to that of pipe body.

A premium connection is defined by :

- More complex thread forms
- Resilient seals
- Torque shoulders
- Metal-to-metal seal

Most premium connections have a double shoulder. (top of the pin , bottom of the box). 

The length of premium connection coupling is longer than that of API coupling. 

Most premium connections have trapezoidal threads for multiple sealing effect.

API threads are sealed by the intermeshing of internal and external threads

For standard premium OCTG connections with the loads expected in drilling with casing applications the Stress Concentration Factors (SCF) is normally higher than 2.0, however from a fatigue perspective it is desirable that the SCF value be as low as possible.

Premium connection has good anti-sticking performance (can be repeatedly lifted and unloaded without damaging the threads)

Example of premium connections compatible with API connections are Vam Eis, DSTJ, GPDS

Hope this is useful for you.

Managing director Punch Energy Services
Punch Energy Services
Total Posts: 18
Join Date: 24/06/20
If it is not API it is not always premium. There are some other around and next to that you have semi-premium (no m2m seal but with a make up arrestor - e.g. DINO VAM) and premium connections (m2m seal - gastight)
In premium you have also a distinction in ISO CAL IV tested and non ISO tested.
Senior Drilling Engineer
Pakistan Petroleum Ltd
Total Posts: 34
Join Date: 02/08/15
14" BTC is Non-API, however, this differs from the manufacturer as to what specs it wants to follow, since we have had instances where 14" BTC of two different vendors did not make up properly.
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