Pitting Initiation of Austenitic and Duplex Stainless Steel in Laying of Flowline in Deepwater

Pitting initiation of Austenitic and Duplex Stainless Steel in Laying of Flowline in Deepwater

With development of oil and gas in deepwater, more and more stainless steels have been used as flowline. However, stainless steels may suffer from pitting in seawater. This research is based on corrosion risk in laying process of subsea flowline.The initiation time of stainless steels immersed in seawater is one of the dominate factor during materials screening, design and laying of flowline.

 In this work, pitting corrosion behaviors of austenitic and duplex stainless steel including initiation, distribution and development of pitting were investigated. Also the effects of temperature, dissolved oxygen, salinity on corrosion were discussed by morphologic characterization of localized corrosion associated with its shape and size description. Another assessment is electrochemical noise (ECN) measurement. During ECN measurements, current fluctuations were recorded using a zero-resistance ammeter (ZRA) and the potential of the pair was recorded simultaneously under steady-state conditions. The results show that temperature, dissolved oxygen, salinity were main factors which affect corrosion behavior of stainless steels in seawater.

Key Words: pitting corrosion, deepwater, flowline, stainless steel, ECN measurement.