The annulus seal assembly is an essential component of the subsea wellhead system, providing hydraulic isolation to other annuli. A failure of that device can lead to a very costly replacement intervention, due to the need of removal of the subsea equipment and production string, or even serious integrity consequences, such as underground blowout or cascade collapse of the casing strings. During the well lifetime, the annulus seal assembly is submitted to various types of loads, depending on the well temperature and the operated pressure of the "A" annulus. The analysis of those loads identified critical moments for the annulus seal assembly, which could exceed the capacity of that device if the proper lock mechanism is not installed, and cyclic loads could further depreciate its capacity. The objective of the present paper is to present a methodology to evaluate the critical loads, failure modes and qualification procedures for long-term well integrity.