5.0. casing design

For Minimum Collapse Failure in the Plastic Range with Minimum Yield Stress Limitations:

Applicable D/t Span

API GRADE D/T RATIO SPAN

H-40 casing and tubing 16.40 and less

K-55 casing and J-55 tubing 14.81 and less

C-75 casing and tubing 13.60 and less

L-80 and N-80 casing and tubing 13.38 and less

C-90 casing and tubing 13.01 and less C-95 casing, X-95 drill pipe, and T-95 casing

and tubing 12.85 and less

P-105 tubing 12.57 and less

P-110 casing 12.44 and less

Q-125 casing 12.11 and less

COLLAPSE PRESSURE

Factors and Applicable D/t Span

For Minimum Failure in the Plastic Range:

API GRADE A B C D/T RATIO SPAN

H-40 2.950 .0465 754 16.40 to 27.01 J-55 and K-55 2.991 .0541 1206 14.81 to 25.01 C-75 and E 3.054 .0642 1806 13.60 to 22.91

L-80 and N-80 3.071 .0667 1955 13.38 to 22.47 C-90 3.106 .0718 2254 13.01 to 21.69 C-95 3.124 .0743 2404 12.85 to 21.33 P-105 3.162 .0794 2702 12.57 to 20.70 P-110 3.181 .0819 2852 12.44 to 20.41 Q-125 3.239 .0895 3301 12.11 to 19.63

Factors and Applicable D/t Ratio Span

For Minimum Failure in Transition Zone Between Plastic and Elastic Range:

API GRADE F G D/T RATIO SPAN

H-40 2.063 .0325 27.01 to 42.64

J-55 and K-55 1.989 .0360 25.01 to 37.21

C-75 1.990 .0418 22.91 to 32.05

L-80 and N-80 1.998 .0434 22.47 to 31.02

C-90 2.017 .0466 21.69 to 29.18

C-95 2.029 .0482 21.33 to 28.36

P-105 2.053 .0515 20.70 to 26.89

P-110 2.066 .0532 20.41 to 26.22

Q-125 2.106 .0582 19.63 to 24.46

Applicable D/t Span

For Minimum Failure in the Elastic Range:

GRADE D/T RATIO SPAN

H-40 42.64 and greater

J-55 and K-55 37.21 and greater

C-75 32.05 and greater

L-80 and N-80 31.02 and greater



P-105 26.89 and greater


Q-125 24.46 and greater

Applicable D/t Span

For Minimum Failure in the Elastic Range:

GRADE D/T RATIO SPAN

H-40 42.64 and greater

J-55 and K-55 37.21 and greater


L-80 and N-80 31.02 and greater





Q-125 24.46 and greater

GRADE FACTORS IN PSI

H-40 40,000

J-55 and K-55 55,000

C-75 75,000

L-80 and N-80 80,000

C-90 90,000

C-95 95,000

P-105 105,000

P-110 110,000

Q-125 125,000

S-135 135,000

Yp = Minimum Yield Strength

Collapse Pressure Under Axial Tension Stress:

Where:

= Minimum collapse pressure in psi

D = Nominal outside diameter in inchesP = Nominal wall thickness in inches

Minimum collapse pressure under axial load can be determined from tables in API Bul 5C2, 20th Edition, 1987.

INTERNAL PRESSURE

Internal Yield Pressure

(Casing, Tubing and Drill Pipe - Minimum Wall)

Where:

Pl = minimum internal yield pressure in psiD = nominal outside diameter of pipe in inchest = nominal wall thickness of pipe in inchesYp = specified minimum yield strength in psi

Internal Pressure of pipe at 80% of Minimum Yield:(Also: Maximum Formation Fracturing Pressure)

Internal Pressure of Coupling

Where:

S = 80% of Yp for mill test pressure and for maximum fracturing pressureS = 100% of Yp for internal yield pressureW (W1 for special clearance) = outside diameter of couplingd1 = thread root diameter of coupling at end of pipe in power-tight position

For round thread casing and tubing couplings:

Where:

T = Included taper on diameterOther symbols are listed in API Std. 5B.

For buttress thread casing couplings:

Where:

T = Included taper on diameterl = 0.400 in. for 4-1/2 in. ODl = 0.500 in. for 5 in. through 13-3/8 in. ODl = 0.375 in. for 16 in. OD and larger

Other symbols are listed in API Std.5B.

Where:

P = internal pressure, psiE = 30 x 106 T = thread taperNp = #. of thread turns make-upp = thread pitchW = coupling ODEs = E1 for round threadEs = E7 for buttress thread

Internal Pressure Leak Resistance:

JOINT STRENGTH

Round Thread Casing

The following equations apply to both short and long threads and couplings. One is for failure by fracture and the other is for failure by thread jumping or pullout; the lesser of the resulting values is listed as the joint strength.

Fracture Strength:

Pullout Strength:

Pj = minimum joint strength in poundsAjp = cross-sectional area of the pipe wall under the last perfect thread, in square inches.Ajp = 0.7854 [ ( D - 0.1425)2 - d2 ]D = nominal outside diameter of pipe in inchesd = nominal inside diameter of pipe in inchesL = engaged thread length in inchesL = L4 - M for nominal make-up, as listed in API Std. 5BYp = minimum yield strength of pipe in pounds per square inchUp = minimum ultimate strength of pipe in pounds per square inch

D *.74 D 0.59

4 - 1/2 .30467

5 .28631

5 - 1/2 .27066

6 - 5/8 .24251

7 .23476

7 - 5/8 .22321

8 - 5/8 .20756

9 - 5/8 .19455

10 - 3/4 .18226

11 - 3/4 .17295

13 - 3/8 .16022

16 .14415

18 - 5/8 .13179

20 .12636

Buttress Thread Casing

For casing with buttress threads, two formulas are used; one is for the strength of the threaded pipe and the other, for the coupling. The lesser of the values obtained by the two formulas governs.

Pipe Strength:

Coupling Thread Strength:

Pj = minimum joint strength in poundsAp = cross-sectional area of pipe, in square inches, 0.7854 ( D2 - d2 ).Ac = cross sectional area of coupling, square inches 0.7854 ( W2 - d1

2 ).D = outside diameter of pipe in inchesd = inside diameter of pipe in inchesd1 = diameter at the root of the coupling thread at the end of the pipe in the power-tight positionW = outside diameter of coupling, inchesYp = minimum yield strength of pipe in pounds per square inchUp = minimum ultimate strength of pipe in pounds per square inchUc = minimum ultimate strength of coupling in pounds per square inch

TENSION YIELD LOAD

Drill Pipe and Round Thread Tubing

Yield strength values for round thread tubing and drill pipe are determined as the product of the specified minimum yield strength for the steel grade and the area of section under the root of the last perfect thread of the pipe or of the area of the body of the pipe, whichever is smaller.

Non-Upset Tubing:

External Upset Tubing and Internal and External Upset Drill Pipe:

Pj = minimum joint strength in poundsD = nominal outside diameter of pipe in inchesd = nominal inside diameter of pipe in inchesh = height of thread in inchesh = 0.05560 in. for 10 threads per inchh = 0.07125 in. for 8 threads per inchL = L4 - M for nominal make-up, as listed in API Std. 5BYp = specified minimum yield strength of pipe in pounds per square inch. Values are listed elsewhere.

5.0. casing design

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