The purpose of this case study is to present 2 failure mechanisms which have contributed to catastrophic mechanical seal failures leading to loss of primary containment (LOPC) at condensate transfer pumps (CTP). The impact of LOPC is more severe if the product itself is hazardous to people, asset environment. Mechanical seal failure may be contributed by many factors such as poor installation, misalignment of seal face cascaded from pump vibration, dry running, over compression, thermal shock or expansion, poor barrier fluid quality, etc. For case# 1 catastrophic seal failure occurred due to presence of free water and sludge in seal barrier fluid which has caused the water vaporization due to high heat generation and low boiling point The thin barrier fluid film between seal faces cannot be sustained leading to face to face contact As a result, chipping of seal face was formed. Meanwhile for case# 2 another failure mechanism was due to poor preservation of spare mechanical seal which has caused the moisture from atmosphere to accumulate at the seal face, creating a slip stick condition and initiate a hairline crack on seal face pin slot due to the high torque from the pump, the hairline crack propagate thru the pin slot at the outboard rotating seal face. The outboard seal cracked, leading to the hammering on anti rotating pin dislodged and subsequently hammered the inboard seal face