API is an acronym for American Petroleum Institute. API is responsible for standardizing equipment used in the oil and gas industry to ensure the safety, reliability and interchangeability of equipment used in the industry. API oil casing is mainly used for the drilling of oil and gas wells and the transportation of oil and gas. It is a large-diameter seamless pipe, which plays the role of fixing the wall or hole of oil and gas oil wells.
Casing leakage accident is an important cause of early failure of oil and gas wells. In order to ensure the high performance of the oil casing when it is working, the casing must be checked for hydrostatic pressure as required. The hydraulic test is to tighten and seal the inner and outer threaded joints of the casing with threaded plugs to make them into a closed container, and then apply the water pressure to stabilize the pressure within the specified pressure and time, so as to check the tightness of the casing. If the pressure test does not leak, the casing is qualified and can be used in the well; otherwise, the casing is unqualified and cannot be used in the well.
API casing hydrostatic test pressure
API stipulates that the purpose of hydrostatic pressure test is to check whether the casing pipe body is leaking, not to check whether the casing joint is leaking. Article 10.12 of API stipulates as follows:Each pipe shall be subjected to a full-length hydrostatic test after thickening (if applicable) and final heat treatment (if applicable), at least at the specified hydrostatic test pressure for 5 s without leakage. The hydrostatic pressure test pressure specified here is the test pressure for inspection, has nothing to do with the working pressure, and cannot be used as a design basis.
API stipulates the casing hydrostatic test pressure as follows:
1) The hydrostatic test pressure of the plain end pipe is calculated according to the formula (1).
Pm=2×f×YSm×tm/Dm (1)
where:
Pm :the hydrostatic test pressure, MPa;
Dm :the outer diameter, mm;
YSm:the yield strength, MPa;
tm:the wall thickness, mm;
f:a factor that depends on the size and grade of the pipe.
2) The hydrostatic test pressure of the coupling is calculated according to the formula (2).
Pm=0.8×YSm×(Wm-d1m)/Wm (2)
where:
Pm: hydrostatic test pressure, MPa;
Wm: outer diameter of the coupling, mm;
YSm: Yield strength, MPa;
d1m: diameter of the root of the coupling thread at the pipe end plane at the machine-tightening position, mm.
3) Resistance to internal pressure leakage at the E1 or E7 plane
The internal pressure leakage resistance at the EI plane of the round threaded joint and the E7 plane of the buttress threaded casing is calculated according to formula (3):
PLRm=E×τ×N×P×[Wm2-Es2]/[2×Es×Wm2] (3)
where:
PLRm : internal pressure leakage resistance at the E1 or E7 plane, MPa;
Wm : outer diameter of the coupling, mm;
E : elastic modulus, 207 000 MPa;
Es : diameter of the seal, mm, the round thread is E1, and the trapezoidal thread is E2;
N : number of tight turns;
P : thread pitch, mm/thread;
τ : thread taper, mm/25.4mm.
4) Hydrostatic test pressure for pipes with threads and couplings
The hydrostatic test pressure for threaded and coupled pipe is the minimum of:
Hydrostatic test pressure of plain end pipe;
Maximum hydrostatic test pressure of coupling;
Internal pressure leakage resistance at the E1 or E7 plane
Measures to ensure the tightness of API casing
1) The design of API casing internal compressive strength shall be based on the internal yield pressure specified in API TR5C3.
2) The internal compression strength design of special threaded joint casing shall implement the minimum internal yield pressure of casing pipe body specified in APITR 5C3.
3) In order to prevent coupling failure accidents in deep wells and ultra-deep wells, the outer wall of the casing coupling should be machined, and "black skin" is not allowed.
4) It is suggested that oilfields should put forward strict requirements on the main performance indicators such as thread grease used for casing make-up, hydraulic test pressure and stabilization time, and yield strength in casing in the form of order supplementary technical agreement.
Casing leakage accident is an important cause of early failure of oil and gas wells. In order to ensure the high performance of the oil casing when it is working, the casing must be checked for hydrostatic pressure as required. The hydraulic test is to tighten and seal the inner and outer threaded joints of the casing with threaded plugs to make them into a closed container, and then apply the water pressure to stabilize the pressure within the specified pressure and time, so as to check the tightness of the casing. If the pressure test does not leak, the casing is qualified and can be used in the well; otherwise, the casing is unqualified and cannot be used in the well.
API casing hydrostatic test pressure
API stipulates that the purpose of hydrostatic pressure test is to check whether the casing pipe body is leaking, not to check whether the casing joint is leaking. Article 10.12 of API stipulates as follows:Each pipe shall be subjected to a full-length hydrostatic test after thickening (if applicable) and final heat treatment (if applicable), at least at the specified hydrostatic test pressure for 5 s without leakage. The hydrostatic pressure test pressure specified here is the test pressure for inspection, has nothing to do with the working pressure, and cannot be used as a design basis.
API stipulates the casing hydrostatic test pressure as follows:
1) The hydrostatic test pressure of the plain end pipe is calculated according to the formula (1).
Pm=2×f×YSm×tm/Dm (1)
where:
Pm :the hydrostatic test pressure, MPa;
Dm :the outer diameter, mm;
YSm:the yield strength, MPa;
tm:the wall thickness, mm;
f:a factor that depends on the size and grade of the pipe.
2) The hydrostatic test pressure of the coupling is calculated according to the formula (2).
Pm=0.8×YSm×(Wm-d1m)/Wm (2)
where:
Pm: hydrostatic test pressure, MPa;
Wm: outer diameter of the coupling, mm;
YSm: Yield strength, MPa;
d1m: diameter of the root of the coupling thread at the pipe end plane at the machine-tightening position, mm.
3) Resistance to internal pressure leakage at the E1 or E7 plane
The internal pressure leakage resistance at the EI plane of the round threaded joint and the E7 plane of the buttress threaded casing is calculated according to formula (3):
PLRm=E×τ×N×P×[Wm2-Es2]/[2×Es×Wm2] (3)
where:
PLRm : internal pressure leakage resistance at the E1 or E7 plane, MPa;
Wm : outer diameter of the coupling, mm;
E : elastic modulus, 207 000 MPa;
Es : diameter of the seal, mm, the round thread is E1, and the trapezoidal thread is E2;
N : number of tight turns;
P : thread pitch, mm/thread;
τ : thread taper, mm/25.4mm.
4) Hydrostatic test pressure for pipes with threads and couplings
The hydrostatic test pressure for threaded and coupled pipe is the minimum of:
Hydrostatic test pressure of plain end pipe;
Maximum hydrostatic test pressure of coupling;
Internal pressure leakage resistance at the E1 or E7 plane
Measures to ensure the tightness of API casing
1) The design of API casing internal compressive strength shall be based on the internal yield pressure specified in API TR5C3.
2) The internal compression strength design of special threaded joint casing shall implement the minimum internal yield pressure of casing pipe body specified in APITR 5C3.
3) In order to prevent coupling failure accidents in deep wells and ultra-deep wells, the outer wall of the casing coupling should be machined, and "black skin" is not allowed.
4) It is suggested that oilfields should put forward strict requirements on the main performance indicators such as thread grease used for casing make-up, hydraulic test pressure and stabilization time, and yield strength in casing in the form of order supplementary technical agreement.
