API Buttress Connection Data Sheet

Table of Contents

The API Buttress Connection Data sheet shows that the casing is externally threaded on both ends of non-upset pipe. The single lengths are joined by an internally threaded coupling. – The thread profile has flat crests and roots parallel to the taper cone with angles 3° and 10° to the vertical of the pipe axis; and 5 threads per inch on a 0,0625 inch per inch taper for sizes 13% inch and smaller, and 0,0833 inch per inch for sizes 16 inch and larger.

API Connections

The American Petroleum Institute (API) has adopted several connections. The API designation indicates that a connection design (generally developed by private industry) has been donated to the public, with the American Petroleum Institute assuming stewardship. The API connections include 8th (pronounced “eight round”-implying eight threads per inch), 10th, Buttress (BTC), and Extreme-Line (XL) designs. API Standards 5B and 5CT contain the geometric, performance, and gauging specifics for the available API connections and address tubing and casing sizes 1.050″ through 20″.

Buttress Connections

API Buttress (BTC) connections are available in pipe sizes ranging from 4-1/2″ to 20″ (Figures 1 & 2). BTC connections larger than 13-3/8″ OD can be subject to cross-threading. Extreme care in the field can ensure the proper makeup of the larger sizes. The shear resistance, large thread cross-section, and ease of running of BTC make it the workhorse of high-tensile casing designs.

Adequate sealability and clearance need to be checked, as with any connection application. Over the years, improved threading practices have enhanced the sealability of BTC. When controlled tin plating is applied, an economical, high tensile, and very leak-resistant connection is achieved.

BTC Pin-Coupling
Figure1: BTC Pin-Coupling
BTC Thread Profile
Figure 2: API BTC Thread Profile

Preparations Hints:

  1. Clean the connection from any dirt with high-pressure water. It is not recommended to use oil as it may leave residue on the connection
  2. Drift the joints from the pin to the box
  3. Secure the joints with a thread protector
  4. Check the upper and lower strings that you will connect to the Buttress connection (X-overs – Subs – Completion Tools – etc.).
  5. Most oil and gas companies will perform a full inspection of casing or tubing, including the connection. If this is not available, go through visual inspection
  6. Note that connecting different materials may cause problems over time. Therefore, make sure that all the string with the same metallurgy.
  7. Refer to API RP 5A3 to check the compatible thread compound. Many experts recommend using API modified thread compound
  8. You don’t need to sink the thread with grease, just a simple thin film of grease on half of the connection will be enough
API Buttress Connection
API Buttress Connection In Data Sheet

Making Up The Buttress Connection

Make-up torque values for buttress thread casing con­nections should be determined by carefully noting the torque required to make up each of several con­nections to the base of the triangle, then using the torque value thus established, make up the balance of the pipe of that particular weight and grade in the string ( Check also: Casing Running Procedure).

Buttress Triangle
Making Up Triangle
  • In the data sheet, Min Make Up For API Buttress connection: One full thread turn before the triangle base.
  • Maximum Make-up: Triangle Base
Making Up The Buttress Connection

The maximum spin while making up the buttress connection should not exceed 15 RPM. Verticality while making up process is important, therefore you will need a stapper in such a job. The values below shall be used as guidelines while making up the Buttress Connections

Makeup torque
Makeup API Buttress Data sheet torque
Makeup torque For API Buttress Data sheet
suggested torque
recommeded M/U T for API Buttress Data sheet connection
Hents for Making up Buttress Connection Data sheet API

API Buttress Casing Connections Make Up Loss Datasheet

OD inchOD mmMake Up Loss (in)Make Up Loss (mm)
4 1/2114.33.9375100
51274.0625103.2
5 1/2139.74.125104.8
6 5/8168.34.3125109.5
7177.84.5114.3
7 5/8193.84.6875119.1
8 5/8219.14.8125122.2
9 5/8244.54.8125122.2
10 3/42734.8125122.2
11 3/4298.44.8125122.2
13 3/8339.74.8125122.2
16406.44.8125122.2
18 5/84734.8125122.2
205084.8125122.2
Makeup Loss

Data Sheet | Coupling Of The API Buttress Connection Dimensions

Coupling Of The API Buttress Connection Dimensions
Coupling Of The API Buttress Connection Dimensions
D [in]D [mm]Nom Wt Ibs/ftd [in]d [mm]t [in]t [mm]W [in]W [mm]Wc [in]Wc [mm]N1 [In)N1 [mm)Threads per inch
4.5114,3010,504,051102,900,2245,705,000127,004,875123,838,875225,435
4.5114,3013,503,917101,500,2486,305,000127,004,875123,838,875225,435
4.5114,3011,603,99697,200,2917,405,000127,004,875123,838,875225,435
4.5114,3015,103,82699,500,3388,605,000127,004,875123,838,875225,435
5127,0013,004,496114,200,2516,405,563141,305,375136,539,125231,785
5127,0015,004,409112,000,2957,505,563141,305,375136,539,125231,785
5127,0018,004,275108,600,3629,205,563141,305,375136,539,125231,785
5127,0021,404,125104,800,43711,105,563141,305,375136,539,125231,785
5127,0023,204,047102,800,47612,105,563141,305,375136,539,125231,785
5127,0024,104,000101,600,50012,705,563141,305,375136,539,125231,785
5.5139,7015,504,948125,700,2757,006,050153,675,875149,239,250234,955
5.5139,7017,004,893124,300,3037,706,050153,675,875149,239,250234,955
5.5139,7020,004,775121,300,3629,206,050153,675,875149,239,250234,955
5.5139,7023,004,673118,700,41310,506,050153,677,000149,239,250234,955
6 5/8168,2820,006,051153,700,2877,307,390187,715,875177,809,625244,485
6 5/8168,2824,005,921150,400,3508,907,390187,717,000177,809,625244,485
6 5/8168,2828,005,791147,100,41710,607,390187,717,000177,809,625244,485
6 5/8168,2832,005,673144,100,47612, 107,390167,717,000177,809,625244,485
7 177,8023,006,362161,600,3148,007,656194,467,375187,3310,000254,005
7 177,8026,006,275159,400,3629,207,656194,467,375187,3310,000254,005
7 177,8029,006,181157,000,40910,407,656194,467,375187,3310,000254,005
7 177,8032,006,094154,800,45211,507,656194;467,375187,3310,000254,005
7 177,8035,006,007152,600,49612,607,656194,467,375187,3310,000254,005
7 177,8038,005,921150,400,53913,707,656194,467,375187,3310,000254,005
7 5/8193,7026,406,968177,000,3288,368,500215,908,125206,3810,375263,535
7 5/8193,7029,706,877174,700,3759,568,500215,908,125206,3810,375263,535
7 5/8193,7033,704,799121,900,43010,978,500215,908,125206,3810,375263,535
7 5/8193,7039,006,625168,300,50012,758,500215,908,125206,3810,375263,535
7 5/8193,7042,806,500165, 100,56214,338,500215,908,125206,3810,375263,535
7 5/8193,7045,306,437163,500,59515,178,500215,908,125206,3810,375263,535
7 5/8193,7047,106,374161,900,62515,948,500215,908,125206,3810,375263,535
8 5/8219,1032,007,925201,300,35208,989,625244,489,125231,7810,625269,885
8 5/8219,1036,007,822198,700,40010,209,625244,489,125231,7810,625269,885
8 5/8219,1040,007,728196,300,45011,489,625244,489,125231,7810,625269,885
8 5/8219,1044,007,625193,700,50012,759,625244,489,125231,7810,625269,885
8 5/8219,1049,007,515190,900,55714,209,625244,489,125231,7810,625269,885
9 5/8244,5036,008,925226,700,35208,9810,625269,8810,125257,1810,625269,885
9 5/8244,5040,008,838224,500,39510,0710,625269,8810,125257,1810,625269,885
9 5/8244,5043,508,759222,500,43511,0910,625269,8810,125257,1810,625269,885
9 5/8244,5047,008,681220,500,47212,0410,625269,8810,125257,1810,625269,885
9 5/8244,5053,508,539216,900,54513,9010,625269,8810,125257,1810,625269,885
10 3/4273,1040,5010,051255,300,35008,9311,750298,4511,250285,7510,625269,885
10 3/4273,1045,509,948252,700,40010,2011,750298,4511,250285,7510,625269,885
10 3/4273,1051,009,854250,300,45011,4811,750298,4511,250285,7510,625269,885
10 3/4273,1055,509,759247,900,49512,6211,750298,4511,250285,7510,625269,885
10 3/4273,1060,709,661245,400,54513,9011,750298,4511,250285,7510,625269,885
10 3/4273,1065,709,559242,800,59515,1711,750298,4511,250285,7510,625269,885
11 3/4298,5047,0011,003279,500,3759,5612,750323,85––10,625269,885
11 3/4298,5054,0010,885276,500,43511,0912,750323,85––10,625269,885
11 3/4298,5060,0010,775273,700,48912,4712,750323,85––10,625269,885
13 3/8339,7054,5012,610320,300,3809,6914,375365,13––10,625269,885
13 3/8339,7061,0012,515317,900,43010,9714,375365,13––10,625269,885
13 3/8339,7068,0012,413315,300,48012,2414,375365,13––10,625269,885
13 3/8339,7072,0012,342313,500,51413,1114,375365,13––10,625269,885
16 406,4075,0015,125384,200,43811,1717,000431,80––10,625269,885
16 406,4084,0015,007381,200,49512,6217,000431,80––10,625269,885
18 5/8473,0087,5017,755451,000,43511,0920,000508,00––10,625269,885
20 508,0094,0019,125485,800,43811,1721,000533,40––10,625269,885
20 508,00106,5019,000482,600,50012,7521,000533,40––10,625269,885
20 508,00133,0018,732475,800,63516,1921,000533,40––10,625269,885

API Buttress Connection Selection Do’s & Don’ts in Data Sheet

  • Confine BTC to 13-3/8 diameter pipe or less. Short strings of 16 to 20 BTC, with tension design factors greater than 6.0, can be used but are not justifiable on rigs with a high day rate. This is due to the difficulty of stabbing and verifying that a proper power-tight make-up has been achieved. If fluid tightness to gas or clear liquids is absolutely required, the couplings must be tin-plated and made up to at least the base of the triangle.
  • Don’t use API casing connections that are coupling weak for internal pressure or axial tension loads (i.e., special clearance BTC and thick wall casing).

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