MIC on level Bridle. Presented by: Amilcar Oberto Corrosion Engineer

Transcription

1 MIC on level Bridle Presented by: Amilcar Oberto Corrosion Engineer

2 Abkatun April 1 st, 2015 Mexican state energy company Pemex, reported that 45 oil and gas workers had been injured. The explosion was caused by a leak in a rarely used gas fuel line, which showed an unusual kind of accelerated corrosion due to the presence of microorganisms and sulfuric acid within the gas.

3 Subject: LP Separator Piping Pin Hole Leak Level Bridle Date: April 6 th 2015 Site: Offshore What Happened: Found a small seep (few drops of oily water) coming from a level control bridle on the Separator. The seep was coming from the inside radius of a 90 degree elbow that was after the first flange off of the vessel nozzle but before the first isolation block valve. This incident highlights the importance of identifying and maintaining barrier health from initial design through to corrosion threat assessment, RBI program implementation, and maintaining good bacteria control to avoid Microbiologically Influenced Corrosion (i.e., MIC is the Probable Root Cause)

4 RCFA Team Process Engineer Integrity Engineer Process Safety Engineer IM Engineer Inspectors Process Analysis Metallurgical Analysis Materials Engineers Third party forensic lab Corrosion Engineers Microbial Analysis Figure 1 - Digital RT Image Bridle Spool Seep Corrosion Engineers Production Chemist Engineers Third party microbial laboratory

5 Actions Taken Spool removed, preserved and send out for metallurgical and bacteria analysis Immediately X-ray other similar piping on both LP1 and LP2 and found three areas of concern on the LP2 Separator which were clamped and are currently in operation. Continue to inspect/x-ray all related piping to identify any other issues. Complete inspections on all uncoated carbon steel pipe spools in water phase service located between the vessel and first block valve on the LP, Test, and IP Separators, and two Treaters. Ongoing with inspections of uncoated carbon steel pipe spools on associated vessels o Recently determined to be the primary source of bacteria to the production system. Expand the biocide program to vessels which are not regularly in the flow path but which periodically flow back into the system. Evaluate current biocide program and product efficacy to reduce MIC. Figure 1 - Digital RT Image Bridle Figure Spool 1 - Seep Digital RT Image Bridle Spool Seep

6 Key Lessons Why this happens? Inspection campaign in produced water (PW) dead leg (DL) targeted the PW system only which was successfully completed. Inspection scope did not include non-pw piping systems such as bridles on vessels and these bridles continued to be a part of the RBI program and DL register with a medium criticality. Bridles in the RBI program seem to have a low probability of failure which resulted in a leak 8 months prior to the scheduled RBI inspection date. X-ray spool examination showed that corrosion was not limited to the pinhole area, metallographic examination revealed features adjacent to the perforation. Bacteria have been identified as major corrosion threat in PW large numbers of microorganism detected across the system Figure 1 - Digital RT Image Bridle Spool Seep

7 Bugs Targets Sulfate Reduction Sulfate reducing microorganism consume hydrogen, produce H2S and are commonly implicated in pitting corrosion Methanogens Methanogens utilize hydrogen for growth, contribute to Cathodic depolarization and cause corrosion rates comparable to SRB Acid Producing Bacteria Mainly fermenters and acetogens. Organic acid production by fermenters support growth of others MIC microorganism and can lead to localize drop in ph. Acetic acid exacerbates carbon dioxide corrosion Iron Reducing Bacteria In addition to consuming hydrogen, IRB reduce insoluble ferric iron to soluble ferrous iron potentially facilitating the removal of protective corrosion products

8 Bugs Analysis Bacteria Quantification on Sample Collected from Pinhole ATP (Adenosine Triphosphate) o Measurement takes only minutes o Provides a good estimation of bacteria numbers present in the sample Location LP1 Spool Internal 4,648,809 ME Bacteria Quantification / Speciation on Sample collected from Pinhole qpcr (Quantitative Polymerase Chain Reaction) o Provides rapid quantitative assessment of microorganism present o Allows bacteria speciation Organism Identified Metabolic Class 1 Risk 2 Characteristics Proteiniphilum APB MIC Capable of acid production; may see elevated MIC due to acetic and propionic acid Dongia sp APB MIC Capable of acid production and may contribute to MIC Flavobacterium sp HDB BF Indirect role in MIC Petrotoga GHB BF Indirect role in MIC/souring Chloroflexus sp GHB BF Indirect role in MIC Geotoga Petraea SuRB H2S / MIC Reduce elemental sulfur to H2S; increases risk of MC Eubacterium sp APB MIC Capable of acid production and may contribute to MIC Synergistes sp APB MIC Capable of acid production and may contribute to MIC Mesotoga Prima APB MIC Capable of acid production and may contribute to MIC Methanogens SRB MIC H2S production

9 Bacteria Consortia * Proteiniphylum acetatigens Anaerobic / microaerophilic, hydrogen producer, gram negative, motile coccobacilli, non spore forming rods that produce acetic and propionic acids

10 Biocide Evaluation Evaluation of different biocides, each at different concentrations conducted on bulk fluids and biofilms grown PW System. Test performed in 2 phases: Phase 1: identified the top biocide from (e.g. THPS, THPS/DBNPA, DBNPA, Glutaraldehyde) candidates and the associated concentration / exposure times that reduces the planktonic/ sessile microbial activity through ATP / Flow Cytometry / CLSM analysis. Phase 2: evaluate product efficacy of the biocide selected from phase 1 against sessile microbes grown and determine the frequency at which the chemical must be reapplied to minimize regrowth and biofilm activity. Biofilm Control Through application of more effective biocide to help prevent or remove biofilm simulating field operating conditions. Sustainable Control Implement solutions that provide sustainable microbial control and meet the regulatory needs. Product Benefits More effective against a broad spectrum of bacteria (Planktonic / Sessile) Environmentally friendly, biodegradable (GoM Approved) Generate chemical alternatives on target sessile populations

11 Biocide Evaluation THPS THPS/DBNPA Blend THPS/Quat Blend Glutaraldehyde Glutaraldehyde/ADBAC Glutaraldehyde/DDAC DBNPA ( 2,2-dibromo-3- nitrilopropionamide) Untreated Biofilm Treated Biofilm

12 Bacteria Control Evaluate Biocide Effectivenes s Against Planktonic and Sessile Deployment & Optimization Select Best Option per Asset Field Trial Evaluate Toxicity

13 Conclusions The corroded spool examination showed that corrosion was not limited to the pinhole area, metallographic examination revealed features adjacent to the perforation No metallurgical defects or deficiencies were detected that could contribute to corrosion damage Analysis confirmed that the wall loss was due to Microbiologically Influenced Corrosion (MIC) / Under Deposit Corrosion The use of MMM quickly allow to properly adjust the biocide treatment plan and reduce the risk of MIC Inspection program for PL small bore piping / level bridle revised and adjusted. Figure 1 - Digital RT Image Bridle Spool Seep

14 Questions