The extrusion process is prone to developing internal stresses on products and tubes.
In many medical devices, multiple tubes must fit together and be sterilized. During the sterilization process tubes are generally subject to high temperatures and this releases stresses in the tubes and the lengths and diameters must be stable for products to function properly. In some cases the parts can shrink up to an inch over a five foot length.
Minnesota MedTec has seen this problem and others similar situations and have created processes to anneal or heat stabilize parts so they don’t shrink out of specification when needed.