This paper shows the engineering path and construction plan applied to convert a single wall ammonia tank into a double wall ammonia tank while operating. The initiative was rooted in concerns about consequences of failure (COF) and a major liquid ammonia release scenario resulting from a Fertilizer Europe (FE) assessment. This paper also presents FE risk assessment results, selection of alternative solutions to reduce risk, design and construction of double walls and tank accessories. Given the operating mode of the tank during project execution, a unique design and exceptional construction method were implemented to build the double wall.