A Case Study of External Cracking in Steam Piping under Mineral Wool Insulation

In recent years, cracking has been observed in carbon steel piping systems operating at temperatures above 70°C. These systems, equipped with mineral wool insulation and aluminum cladding, experienced cracking and failures under normal operating pressures and temperatures. Leachates from wet mineral wool insulation are suspected of causing external stress corrosion cracking (SCC) in these scenarios. A failure in a carbon steel steam condensate return pipe occurred at 50 PSI(g) and 330°F. Gaps in the insulation cladding allowed moisture to accumulate, which led to external stress corrosion cracking, particularly at the underside of the pipe where moisture collects. Material samples taken from the failed pipe showed intergranular cracking and grain elongation at the base of the cracks. This paper summarizes the findings of the investigation into the steam condensate piping failure, aiming to raise industry awareness and promote the safe operation of similar systems.