The use of stainless steel such as Type 316L does not usually present a risk of corrosion when used in fresh water containing low chloride. However, the importance of defining and implementing a robust water management plan during hydrotesting, wet lay-up, flushing and commissioning activities, particularly where stainless steel is involved should not be underestimated. The presence of some waters within stainless steel systems following hydrotesting and commissioning activities can pose significant corrosion risk. Often this can occur due to improper or incomplete draining and drying and is made worse by the presence of bacteria, solids or sediments, and oxygen.

quality used for commissioning is not properly managed. Several months after the completion of commissioning activities and prior to introduction of hydrocarbon, several through-wall corrosion failures were detected in Type 316L pipework at a newly constructed production facility. The failures delayed startup of the plant that required an intensive inspection, mitigation, and repair campaign to assure the plant was fit for startup. It was later discovered that during commissioning activities, a batch of water with unknown provenance and quality entered the system (a mixture of Type 316L and low alloy steel pipework). The questionable water was mixed with water already within the system and moved around various parts of the plant as part of dynamic commissioning activities. Following commissioning and gravity draining of the pipework, the system was left at ambient conditions in contact with air for approximately 9 months prior to the first corrosion failure. Most of the corrosion defects were located within proximity to Type 316L girth welds, and it is believed a chloride pitting mechanism resulted in the corrosion failures. It is also believed the susceptibility of the material was enhanced due to the presence of bacteria.

A discussion of the importance of implementing a robust water management plan to prevent corrosion failures is provided.