High collapse tubing and casing
Definition
High collapse casing is the casing whose collapse resistance is above 15% over the standard data of API 5C2.
Design principle
In accordance with the requirements of API BUL 5C3 for casing collapse and the requirement of inspection and device of oil field, we take the following measurements when the specification and grade is fixed.
A.Decrease the residual stress of casing
B.Improve the accuracy of wall thickness
C.Improve the material’s yield strength
D.Control pipe body conicity
Raw materials
After reserch and trial production, the raw material for the production is limited to two brands 25 Mn2V and 30CrMo. The mechanical property of 25 Mn2V can fully meet the requirement of collapse resistance of the high collapse casing.
30CrMo has better material stability and as a kind of steel its hardenability is better owing to high content of elements like Cr, Mo and Mn. Meanwhile, carbon content is low and can undergo water quenching and oil quenching.
Our company choose 25 Mn2V as the raw material for the production of high collapse casing.
Performance & Parameter
A. Mechanical property
|
Size |
Yield Strength (MPa) |
Tensile Strength (MPa) |
Elongation
(%) |
Impact
(J) |
|
114.3×6.35 |
871~1062 |
≥948 |
≥15 |
≥52 |
|
114.3×7.37 |
B. Residual stress control
Residual stress control or yeild strength 20%
Property
A. Mechanical property
|
Size |
Yield Strength (MPa) |
Tensile Strength (MPa) |
Elongation (%) |
Impact (J) |
|
114.3×6.35 |
955 |
980 |
19 |
65 |
|
114.3×7.37 |
930 |
973 |
18.5 |
94 |
B. Measurement of residual stress
Test of residual stress adopts Cutting Ring Method and the length of cuting ring is 3 times of the extermal diameter. Residual stress calculation formula is as below :
Σr=ES(1/Do-1/Df)/(1-μ)
Σr－Residual stress of the pipe body surface, MPa
E－Modulus of elasticity, E=2X10Pa
S－Average thickness, mm
Do－Average value of external diameter before slotting, mm
Df－Average value of external diameter after slotting, mm
μ－Poisson’s ratio,μ=0.3
|
Sample No. |
Yield Strength MPa |
Residual MPa |
Residual/Yield Strength % |
|
114.3×6.35 |
955 |
14.3 |
15.0 |
|
114.3×7.37 |
930 |
13.8 |
14.8 |
