Valhall Corrosion Events and Management

Transcription

1 Valhall Corrosion Events and Management Learning Pack Eldar Larsen, Head of Operations, BP Norway.

2 Valhall Corrosion Events - Summary Summary Hydrocarbon leak HIPO on 6th March 2009 caused by Microbial Induced Corrosion (MIC) resulted in crude and gas leak, First Aid Incident, emergency plant shutdown & muster. Valhall eventually shutdown for 10 weeks for corrosion inspection and repairs. during which three further incidences of MIC and 44 anomalies identified. Major Lessons Behaviours of MIC were misunderstood Areas of high flow rate were previously thought unlikely to experience MIC, this assumption failed to identify internal pipe work scaling can provide environment for MIC activity. Inadequate application of hazard Recognition, risk awareness and control of work. The initial inspection routine was inappropriate and directly led to exposure of the individual and the resultant FAI. 15 specific improvement opportunities identified as a result of the incident and plant investigations (7 organisational, 5 work process and 3 performance management). INTERNAL DISTRIBUTION ONLY 2

3 Microbial Induced Corrosion What is MIC? MIC is Microbial Induced Corrosion. MIC of carbon steel typically manifests itself as localised corrosion or pitting attack following the development of a surface biofilm. The anaerobic environments of oil and water transport pipework often support the growth of biofilms, which almost invariably contain sulphate-reducing bacteria (SRB), a major cause of MIC. SRB containing biofilms generate H2S. H2S results in formation of Iron sulphide within the biofilm. Iron sulphides are cathodic to bare steel and can have the effect of greatly increasing corrosion at anodic sites. Why does MIC occur? MIC can occur in all systems that contain water with SRB s. Prediction of corrosion rates attributed to MIC is unreliable uncertainty of the onset of localized corrosion/pitting,whether it proceeds at a constant rate. Parameters that can influence MIC include ph, temperature, nutrition, velocity of fluids, presence of deposits. MIC is more likely to occur at locations with low fluid velocity such as in dead legs, under deposits, scale. All metals are susceptible to MIC. Carbon steels have generally been found to be most susceptible. MIC mitigation relies on effective biocide dosing regimes. INTERNAL DISTRIBUTION ONLY 3

4 INTERNAL DISTRIBUTION ONLY 4 Reference - Valhall Timeline 1982 Valhall start production, Incl. Jet washing separators using seawater. By mid- 90 s using mainly produced water 1998 New Metering Skid installed. Small bore pipe work not commissioned in Workmate 1999 RBI Analysis performed MIC internal corrosion not sufficiently identified as a threat Inspection scheme constructed which identified external inspection of Liquids metering package as a whole Chemical cleaning of fast loop to aid calibration due to scale build up Ongoing Biocide treatment of Sulphate Reducing Bacteria (SRB) on Produced Water (PW) system ongoing and working 2007 SRB s in 2nd stage separator 0-460/ml Sept 2007 Cor. Mngt. Health Check: Valhall Prod. Water Sulfate Reducing Bacteria (SRB) contamination as a high risk and recommends a microbial audit by microbial specialist 06.Mar.2009 Leak in 1 pipe fast loop HIPO 02.Apr.2009 Upstream skimmed oil tank 17.Apr.2009 Leak in 6 prod. water pipe

5 Reference - Valhall Timeline Events and response: 6th March 2009 Metering fast loop (F&G ESD). Limited awareness of MIC, deemed low probability. Limited spot checking by X-ray outside the fast loop. No SD justified by residual corrosion risk. No additional resources. 2nd April 2009 T-337 pressure increase (No ESD). Start up after a compressor incident increased flare backpressure which burst a MIC in the produced water system. 15 days (6 + 9) shutdown looking for MIC with Eddy current and X-ray w. crew of 3. 17th April produced water pipe (No ESD). Restart attempt failed when a MIC burst in the prod. water system. Had been inspected in very close vicinity. Increasing realization of the criticality of adequate inspection rigour. 10 days shutdown, 100% inspection of prod. water system by Eddy current and X-ray, extended risk based approach. Increased offshore resources. 27th April 2009 Condensate return to prod. water system. (F&G ESD). Pipe burst during start up attempt. Contained highly volatile condensate. Realized technology gap. Changed to SLOFEC scanning successfully. 30+ team offshore. Task force onshore. True 100% inspection beyond produced water. RIB revision. 1st June 2009 Successful restart. 10 weeks of production loss and serious HSE incidents. INTERNAL DISTRIBUTION ONLY 5

6 Valhall Corrosion Event (March 6 th 2009) Summary of first event. Hydrocarbon leak on metering skid First Aid Incident Emergency Plant Shutdown A seep or sweating leak observed coming from an insulated 1 carbon steel pipe was prepared for inspection following removal of the insulation. The pipe was on the crude export metering skid and contained a mixture of crude oil and gas at 25 bar pressure. On removal of insulation, the leak was observed not to originate from the flange as originally expected. An inspector examining the pipe initially used a blade to scrape off paint at the leak site. During a later visit, the inspector touched the leak site with his finger and was sprayed in the face with oil under pressure. During hydrocarbon release, the hole enlarged to 10mm diameter. Valhall went to full Emergency Shutdown and muster. INTERNAL DISTRIBUTION ONLY 6

7 Hazard Barrier Diagram Heirarchy of control Bias towards hardware/inherent safety & reducing the scope for human error multi barrier defence Relief and Blowdown system Learning from the Past Operations Procedures Effective Supervision / Leadership Audit & Self Regulation Active & Passive Fire Protection Rescue & Recovery Investigation & Lessons Learned Inherent Design Plant Layout Control, Alarm & Shutdown system Maintenance & Inspection Work Control Training & Competency Management of Change Escape / Access Support to Next of Kin & Injured HAZARD Hydrocarbon Inventory at 25bar in Fast Loop line HAZARD REALISATION Loss of containment Actions from 2007/2008 Health Checks to improve Biocide treatment and to conduct Microbial survey not completed Force Inspection procedures inconsistent with requirements of HSE Directive for visual inspection Failure to follow CoW and RBI procedures First Aid injury & HiPo Inspection (RBI) and Corrosion Management practices failed to identify and mitigate the internal corrosion threat/risk that led to the failure RBI assessment not updated to reflect changes to operating and/or process conditions Inadequate Hazard Recognition and Risk Awareness job treated as routine and Level 2 work permit. CoW - Failure to isolate energy source prior to work CoW - Failure to comply with requirements for Visual Inspection Four Point Check not used. Inspection Engineer delegated inspection task to NDT Technician. No apparent MoC for chemical treatment of Fast Loop line. 1 line not identified on riskbased inspection schedule INTERNAL DISTRIBUTION ONLY 7

8 Valhall Corrosion Event (April 2nd 2009) Summary of second event. Targeted inspected discovers further incidence of MIC A leak in the Produced Water System followed a gas compression upset. Area isolated & upstream vessel drained. 25mm hole found in drain line. Areas of low flow and dead-legs were identified and inspected. 6 further MIC incidents observed. Investigation initiated to ensure appropriate analysis and response prior to restart. Management verification of process mitigations and corrosion mapping & repair effort. INTERNAL DISTRIBUTION ONLY 8

9 Valhall MIC Response The third event: Defining the Scope of Work Unpredicted nature and location of corrosion required a new approach to immediate reaction inspection. Produced Water identified as being the main host of Sulphate Reducing Bacterias (SRB s) Considered potential contamination of other systems vs HC leak risks. Scope agreed by Ops, Process TA, Corrosion Mgmt TA, Inspection & CM Contractor. Produced Water System was 100% inspected. Risk Based Hotspot Execution Water wetted surfaces eg Low spots, Sumps, Deadlegs etc. Waste injection on drilling platform (DP). Well systems, confined to slurry lines. Crude Oil processing including the metering system. Closed Drains System. Oil Return from PW Flash Drum to Oil Return tank Orientation of defect; 9 o clock position on vertical pipe INTERNAL DISTRIBUTION ONLY 9

10 Valhall Corrosion Event. Summary of forth event. Targeted inspected discovers further incidence of MIC in high flow pipework Leak in 6 produced water high flow pipework A 8 mm hole was discovered during preparation for plant restart following inspection program triggered two gas detectors & ESD. Critical Factor 1 Microbial induced Corrosion (MiC) mechanism in the produced water system Critical Factor 2 Inspection (RBI) and Corrosion Management practices failed to identify the corrosion risk in high level, high flow pipework INTERNAL DISTRIBUTION ONLY 10

11 Valhall MIC project Inspection Following fresh focussed risk assessment an intense and prioritised inspection programme was initiated. No. 10 T-337 Flange corrosion Extensive inspection effort required to execute identified scope 30+strong team. SLOFEC technology used Priority 1 scope Identified 44 anomalies 23 MIC Related 21 Non-MIC-related 19 spools replaced, 5 temporarily repaired & 20 scheduled for ongoing inspection following start-up Assurance processes followed by No go/go verification reviews Priority 2 inspection scope identified for post start up inspection. INTERNAL DISTRIBUTION ONLY 11

12 Lessons Learnt Direct cause Cross contamination of oil production system with SRB via the produced water system. Inadequate awareness, inspection and mitigation as analysis did not identify oil system as at risk from SRB corrosion. Insufficient chemical injection (such as biocide and corrosion inhibitor) and sampling and analysis to control microbial activity. As a result MIC occurred within oil systems. Underlying causes Improvement opportunities identified within: Organization (7 subcategories with recommendations) Work Processes (5 subcategories with recommendations) Performance Management (3 subcategories with recommendations) INTERNAL DISTRIBUTION ONLY 12