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Summary for casing and tubing failure modes

Casing and tubing is an important material and equipment in the petroleum industry and it has a great amount of use. Casing pipe and pipe string failure will lead to the entire pipe string can not work normally and you will see a lot of casing and tubing corrosion in the construction site. Based on this, the applicability evaluation of casing and tubing with suspected defects is proposed, not only you can make a judgment on the quality of the tubing, but also you can regulate the tubing which doesn’t meet the standards.

The working condition of casing and tubing is relatively poor, and the stress state is complex, so the failure mode is varied, and the failure analysis is summed up in the following 3 types:

Deformation failure

In practical applications, due to the radius of casing and tubing is much smaller than that of the license, instantaneous plastic bending deformation is usually occurred in casing and tubing. It will cause permanent bending of casing and tubing (commonly known as dead bending) in a long time.

In addition, flexible deformation beyond the tensile limit, exceeding the limit of deflated or compressed phenomenon are all part of the deformation failure.

Fracture failure

fracture failure

Fracture failure in the casing and tubing is a large proportion of failure fracture, especially the fatigue fracture that damage is more serious. The main fracture forms are:

Surface damage failure

Surface damage mainly includes 3 forms:

surface corrosion of oil pipe


Most of the tube failure accident occurred in the transition zone of the thickened transition, which accounted for 70%. The reason of failure is that the structure is not reasonable, resulting in stress concentration and corrosion fatigue. Central tube failure accident accounted for 30%. The cause of failure is the interaction of wall thickness thinning caused by abrasive wear and corrosion pit.

quality of casing and tubing

Proposed to strengthen the inspection of the pipe body before welding and deal with the serious internal corrosion to ensure the quality of the tube;
Ultrasonic inspection is carried out around the thickening transition zone of the oil pipe to check whether there is any defect in the transition zone. Length of transition zone and arc radius of oil pipe should be checked before welding, where thickened inner transition zone <100mm, R <300mm are not to be welded;
Strengthen the management of drilling fluid, the pH value of drilling fluid should be maintained at 10 or more than 10 under the condition permission.


With the increasing demand of the drilling industry, the oil pipe is easy to damage under the long-term high temperature and high pressure and unexpected accidents are common occurrence. So it is urgent and important to analyze the failure of tubing. Timely measures can improve the utilization of resources, avoid economic losses, and bring greater social and economic benefits.

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