Top-of-Line Corrosion Mechanisms for Sour Wet Gas Pipelines

Large diameter subsea pipelines operating mainly in stratified flow are being used across the world for wet gas transportation over significant distances from offshore fields to onshore facilities.  Understanding corrosion mechanism occurring at the top of the line under dewing conditions is a key component of operations corrosion management strategy to ensure long-term pipeline integrity and for maintaining un-interrupted gas supply chain. 

The challenge in predicting corrosion in sour systems is due to the varied nature of iron sulfide scales formed over the expected subsea pipeline flow, temperature ranges, and condensation rates that result in different corrosion mechanisms.  Current industry practice is to use sweet system corrosion prediction methodologies to establish the risk of top of line corrosion in sour systems.  This paper will demonstrate the inadequacy of this approach through field validated laboratory results while presenting the applicable mechanism for top of line corrosion in sour systems and propose operational practices to manage the risk of top of line corrosion in large diameter subsea wet sour gas pipelines.