Ballooning is a change in average pressure which causes a radial contraction or swelling. If the tubing is free to move, the length of tubing will be either longer or shorter. If tubing cannot be moved, stress will be created in the tubing body.
Figure 1 illustrates ballooning of tubing. This will happen when internal pressure is higher than external pressure. Tubing will shorten if the tubing is free to move. If the tubing cannot be moved, ballooning will create a tension force on the packer.