Pipe Connectors

Pipe sections are joined with either the thread-and-coupled connectors or are integral connected. Couplings can be used to join two ends of the pipe, as shown in Fig. 11-6. This illustration depicts the three types of coupled connections standardized by the API, The dimensions for various couplings are given in Tables 11-9 and 11-10.

Many coupled connections are non-API and are often termed premium connections. They may have special corrosion or leak resistance characteristics. In addition, they may have a smaller outer clearance than API coupled connections (see Fig. 11-7).

Buttress Casing ThreadsThread Dimensions Casing
Buttress thread casing and coupling

Fig. Í 1—6 STC, LTC, and BTC-coupled API connections (Courtesy American Petroleum Institute)

Table 11-9 Round-Thread Casing Coupling Dimensions, Weights, and Tolerances

Table 11-9 Round-Thread Casing Coupling Dimensions, Weights, and Tolerances

Size*

Outside Diameter, W

Minimum Length

Diameter of Recess, Q

Width of Bearing Face, b

Weight, lb

Short Nl

Long Nl

Short

Long

4Vi

5.000

6'A

7

4'%2

%2

8.05

9.07

5

5.563

6 Vi

7%

5%2

3/l6

10.18

12.56

m

6.050

6%

8

5'%?

Vs

11.44

14.03

6%

7.390

7%

8%

62%2

Va

19.97

24.82

7

7.656

VA

9

IVii

V.6

18.34

23.67

7Vs

8.500

7 Vi

9 Va

72%2

Vi

26.93

34.23

m

9.625

7%

10

82%2

%2

35.58

47.48

9%

10.625

13A

10 </2

92%2

%2

39.51

55.77

10%

11.750

8

-

102%2

%2

45.53

11 3/4

12.750

8

-

112%2

%2

49.61

13%

14.375

8

-

13

y>6

56.23

16

17.000

9

-

1 6"/'3 2

78.98

18%

20.000

9

-

182%2

¥>6

118.94

20

21.000

9

i m

20% 2

S/,6

98.25

126.74

Tolerance on outside diameter W. ± [ percent but not greater than ± '/a ¡11. ♦The size of the coupling is the same as the corresponding pipe size Courtesy American Petroleum Institute

Tolerance on outside diameter W. ± [ percent but not greater than ± '/a ¡11. ♦The size of the coupling is the same as the corresponding pipe size Courtesy American Petroleum Institute

Table 11-10 Buttress Thread Casing Coupling Dimensions, Weights, and Tolerances

Table 11-10 Buttress Thread Casing Coupling Dimensions, Weights, and Tolerances

Size*

Outside Diameter, W

Minimum Length

Diameter of Recess, Q

Width of Bearing Face, b

Weight, lb

Short Nl

Long Nl

Short

Long

4!/2

5.000

4.875

m

4.640

l/s

10.11

7.67

5

5.563

5.375

9V%

5.140

%2

12.99

8.81

5 Vi

6,050

5.875

9'A

5.640

%2

14.14

9,84

6%

7.390

7.000

9%

6.740

Vi

24.46

12.44

1

7.656

7.375

10

7.140

%2

23.22

13.82

7%

8,500

8.125

10%

7.765

s/to

34.84

20.45

PA

9.625

9.125

10%

8.765

%

45.94

23.77

9%

10.625

10.125

10%

9.765

%

50.99

26.47

10%

11.750

11.250

10%

JO.890

%

56.68

29.49

im

12.750

10%

11.890

%

61.74

--

im

14.375

10%

13,515

%

69.95

—-

16

17.000

10%

16.154

%

87.56

18%

20.000

--

10%

18.779

%

138,03

20

21.000

10%

20.154

%

110.33

Tolerance on outside diameter W, ± 1 percent but not greater than ± Vt in. Tolerance on outside diameter \V0, + fe, -'/« in. 4iThe size of the coupling is the same as the corresponding pipe size Courtesy American Petroleum Institute

Tolerance on outside diameter W, ± 1 percent but not greater than ± Vt in. Tolerance on outside diameter \V0, + fe, -'/« in. 4iThe size of the coupling is the same as the corresponding pipe size Courtesy American Petroleum Institute

Non Api Drill Pipe Sizes
Fig. 11-7 Coupled non-API pipe: (a) Hydril's CTS-4, (b) At I as-Bradford's TC-4S Quadra seal
Atlas Bradford Tubing Connections

Fig. H-S Integral connections: (a) Hydril's Tripleleal, (h) Atlas Bradford's 1J-4S Quadraseal

Integral connections do not use separate coupling devices. The ends of tiie joints are milled so the pin end of one joint screws into the box end of another joint. Manufacturers offer a variety of coupled and integral-joint connections (see Fig. 11-8).

Coupling selection is normally based on design criteria such as the following:

  • burst
  • collapse
  • joint strength
  • corrosion resistance
  • leak resistance

Since many investigators have documented casing and tubing failures due to the couplings, proper evaluation and selection is an important issue. It is advisable to consider premium couplings if corrosion, leak resistance, or high pressures are considerations. Coupling manufacturers and distributors should be consulted in these cases. Example 11.6 illustrates coupling selection in a high pressure environment.

Example 11.6

The Wisler-Burnett Oil Company intends to run a 22.300-ft string of 47.0-Ib/ft, P-l 10 grade, 7.625-in. production casing. The maximum expected burst pressure is 14,000 psi. Select the appropriate couplings. A 17.0-lb/gal mud will be used in the well. Company policy dictates that the tension design factor is 1.8. Use the tables in the Appendix.

Solution:

1. Determine the maximum tension load: Pipe weight = depth X lb/ft

  • 22,300 ft X 47.0 lb/ft
  • 1,048,100 1b

Buoyed weights — pipe weight x buoyancy factor

Design load = buoyed weight x design factor

2. The tables in the Appendix provide the following information:

Coupling Type LTC BTC

Burst Rating, psi ¡4,430 13,460

Joint Strength, lb

1,353,000 1,545,000

  1. The LTC coupling is unsatisfactory for the joint strength requirements, while the BTC is underdesigned in burst.
  2. Some of the design options are as follows:
  • run LTC or BTC couplings, realizing they do not meet the design requirements
  • reevaluate the burst criteria
  • reduce the tension design factor

5. This example illustrates that stringent operating conditions may place demands on pipe design beyond the "standard" situation, such that conventional design procedures are not applicable.

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Responses

  • rorimac
    Can a STC PIN screw in a LTC Box connection?
    9 years ago
  • darnell
    What do ltc casing threads look like?
    7 years ago

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