51313-02468-Internally Corroded High Pressure Pipeline Affected by MIC and Settling of Free Water—A Case Study

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Product Number: 51313-02468-SG

ISBN: 02468 2013 CP

Author: Henk Chin A Lien

Publication Date: 2013

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In 2009 an in-line pipeline inspection with magnetic flux technology was done in a 55 km 14 inch high pressure pipeline at Staatsolie in use since 1992 for transportation of mainly clean oil (< 1% water). It revealed that on one section (5.5 Km length) between two facilities 78% of the reported 870 metal loss groups to be internal and to occur at the pipe bottom. Since 2001 this section is used solely for transporting production flow (>20% water). Further investigation revealed very serious amount of Sulphate Reducing Bacteria (SRB 108 count) to be present in the fluid. On the remainder of the 14 inch pipeline used solely for transporting clean oil 98% of the reported 494 metal loss groups where external. This pipeline is protected against external corrosion by a coating layer and cathodic protection while regular internal cleaning by pigging is done. Internal corrosion was measured twice per year with corrosion coupon.
A chemical treatment program consisting of Biocide and Corrosion inhibitor was initiated on fluid entering the pipeline. Internal corrosion monitoring was expended with corrosion probes. SRB count (28 days zero dilution method) was done to monitor the effect of treatment.
The objective was to maintain pipeline integrity by mitigating MIC with chemical treatment.
Corrosion rates measured with both probes and corrosion coupons showed a gradual decline to moderate rates (1- 4.9 MPY ) as the chemical treatment progressed. The probes are however susceptible to bio fouling due to SRB deposition. Dosage and frequency of both injected chemicals was adjusted based on the results. Bacteria count in the fluid dropped significantly to 104 SRB count.
In a pipeline environment with high water cut (> 20%) low velocity high SRB count (> 106) internal corrosion can be mitigated by using a combined Biocide and Corrosion inhibitor chemicals treatment and pigging of the line.
A pipeline integrity solution is:
• chemical treatment for MIC and low velocity flow in pipelines
• monitoring of internal corrosion in an environment with MIC and low velocity flow
• in-line inspection as a tool to determine actual pipeline status.