MIC on level

Bridle

Presented by: Amilcar Oberto Corrosion Engineer

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.

Abkatun – April 1st, 2015

Subject: LP Separator Piping Pin Hole Leak Level Bridle Date: April 6th 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)

Figure 1 - Digital RT Image

Bridle Spool Seep

RCFA Team

Metallurgical

Analysis

Microbial

Analysis

Process Analysis

• Process Engineer • Integrity Engineer

• Process Safety Engineer • IM Engineer • Inspectors

• Materials Engineers • Third party forensic lab

• Corrosion Engineers

• Corrosion Engineers • Production Chemist Engineers • Third party microbial laboratory

• 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 Spool Seep

Actions Taken

Figure 1 - Digital RT Image

Bridle Spool Seep

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

Key Lessons

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

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

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 Class1 Risk2 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

Bugs Analysis

Location ME

LP1 Spool Internal 4,648,809

Bacteria Consortia

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

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

Biocide Evaluation

• THPS

• THPS/DBNPA Blend

• THPS/Quat Blend

• Glutaraldehyde

• Glutaraldehyde/ADBAC

• Glutaraldehyde/DDAC

• DBNPA ( 2,2-dibromo-3-

nitrilopropionamide)

Untreated

Biofilm Treated

Biofilm

Bacteria Control

Evaluate

Biocide

Effectivenes

s Against

Planktonic

and Sessile

Select Best

Option per

Asset

Evaluate

Toxicity Field Trial

Deployment

&

Optimization

• 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

Conclusions

Questions…