Piping systems for industrial purposes are never truly immobile. Constantly changing temperatures and pressures, along with operational vibrations and the way they were installed,are always influencing how pipes behave in a given system.
When combined with environmental factors (such as in refineries, marine systems and power generation). these factors can create prolonged stress inside an otherwise rigid system. This stress, if not properly managed, leads to fatigue leaks, cracks and failures resulting in a high cost of down-time for the facility.
Source: https://flexibel.ae/blog/what-are-expansion-joints