The ASTM D7660-2020 Standard Guide provides a standardized method for performing internal stress testing on United Nations (UN) Certified Encasement. Its purpose is to establish consistent testing practices to ensure that Encasement designs meet specified pressure capacity requirements. The Guide details the steps, equipment requirements, and documentation recommendations for internal and hydrostatic stress testing to help achieve stable test results. This guide is for liquid Encasement designs that comply with U.S. Department of Transportation and United Nations shipping codes and provides additional information to support regulatory requirements to ensure that Encasement can withstand internal and external pressures during transportation.