Most casing failures occur at connections. These failures can be attributed to:

• Improper design or exposure to loads exceeding the rated capacity
• Failure to comply with makeup requirements
• Failure to meet manufacturing tolerances
• Damage during storage and handling
• Damage during production operations (corrosion, wear, etc.)

Connection failure can be classified broadly as:

• Leakage
• Structural failure
• Galling during makeup
• Yielding because of internal pressure
• Jump-out under tensile load
• Fracture under tensile load
• Failure because of excessive torque during makeup or subsequent operations

Avoiding connection failure is not only dependent upon selection of the correct connection, but is strongly influenced by other factors, which include:

• Manufacturing tolerances
• Storage (storage thread compound and thread protector)
• Transportation (thread protector and handling procedures)
• Running procedures (selection of thread compound, application of thread compound, and adherence to correct makeup specifications and procedures)

The overall mechanical integrity of a correctly designed casing string is dependent upon a quality assurance program that ensures damaged connections are not used and that operations personnel adhere to the appropriate running procedures.