Which of the following is true for Pipe Buckling?

• A. It happens when the average pressure inside and the outside pressure of the tubing string are equal and shortening of length because of the tubing being in a spiral shape
• B. It is caused by the change in the average pressure of the formation and the outside pressure of the tubing string and shortening of length because of the tubing being in straight shape
• C. It is caused when the average pressure inside the tubing string is greater than the outside pressure of the tubing string and shortening of length because of the tubing being in a spiral shape
• D. It happens when the change in the average pressure of the formation and the outside pressure of the tubing string are equal