thickness of butress thread

[nightfire007]

we have purchased a casing with size of 18 5/8 inches , but the thickness at the end of thread is much lower than the body thickness and exceed the minus 12.5% which has been mentioned in the API 5CT for body.
i know due to the taper, certainly the thickness at the end is lower than casing body, but i do not find the exact tolerance
so i want to know is there any clause in the API 5CT or API 5B for checking the thickness at the edge of casing after threading or does it cause any problem in future applications.
furthermore, since API 5CT only offer the tolerance for the body of casing , and not the thickness after threading, is it required to check the thickness at the end of the casing ( i.e at both edge) after threading.

 

[johnchrc]

Thickness (ID) is dependent on pipe weight and will be thinner at end because it is a tapered pipe joint. There is another API Spec for Gauging and Inspection of Threads that has the profile and dimensions you want to see.

For 18-5/8 taper is 1" TPF on diameter, 5 TPI with .062 thd height. The theoretical taper starts at 18.365 at pin end. There is a 25 degree lead in chamfer, 3.125" long P.T., and 4.613" length to last scratch. The base of the API Triangle is 4.813". Of course the pipe OD is 18-5/8 +/- API 5CT calc.

Your box would be torqued to the midpoint of the triangle after applying API modified pipe dope to Box and Pin with mustache brush so no metal is exposed. DO NOT OVERAPPLY OR glob onto one spot. Do not use a Bottle Brush to apply thread compound. Keep dope covered at all times and be sure to mix dope the first time you open a can. You may see oil at the top. Do not pour out, mix it in thoroughly with dope.

An 87.5# casing would have a 17.755 ID with a large tolerance and a drift of 17.568".

Your coupling will remain 20" OD regardless of weight.

I hope this helps.

Regards,

- CJ