MEC&F Expert Engineers : 11/24/14

Monday, November 24, 2014

HYDROGEN SULFIDE (H2S) GAS RELEASE FROM PIPING CORROSION FAILURE NEAR A WELD AT AN OIL PLATFORM

Hydrogen Sulfide (H2S) Gas Release from Piping Corrosion Failure Near a Weld at an oil platform

Hydrogen sulfide corrosion has been plaguing the oil and gas industry for many decades. Unless this issue is addressed in areas where high concentrations of hydrogen sulfide are expected or have been measured, catastrophic failures have and will continue to occur.

The Incident

The location of the H2S release was on Platform Hidalgo on Lease OCS-P 0450. This is offshore the California coats. It occurred on February 23, 2012.

A hydrogen sulfide (H2S) gas release occurred from a piping corrosion failure near a weld, on the 8-inch side of an 8-inch by 4-inch reducer on the blowdown line for a third-stage section compression scrubber. Multiple H2S sensors detected the release and initiated a platform shutdown. Platform personnel were directed to muster to the safe briefing areas. Response personnel using breathing apparatus isolated the leak. No injuries to any personnel occurred from the incident. Prior to the platform being restarted, the failed spool was removed and saved for testing, and a new spool was installed. The H2S concentration at the release point was estimated to be 40,000 ppm.

Investigation

An incident investigation revealed the following:

The cause of the H2S release was a weld failure on the side of the reducer. This failure was caused by accelerated corrosion resulting from elemental sulfur in contact with steel in an area where deposits could build up. Elemental sulfur acts as an oxidizer and is known to accelerate steel corrosion and cause localized reduction in wall thickness. The elemental sulfur in the scale was the result of oxygen contamination in the wet, sour gas stream. Oxygen reacts with hydrogen sulfide in liquid water to form elemental sulfur.

Contributing factors to the accelerated corrosion include: high H2S concentrations sufficient to introduce elemental sulfur which exacerbates the corrosion process and low flow rate in the area of the failure due to the reducer configuration. The areas in the reducer with higher flow rates did not have heavy buildup of corrosion products.

The reducer spool that failed is included in a piping circuit in the operator’s Mechanical Integrity Program. The circuit was last examined in May 2011 utilizing a non-destructive test (NDT) ultrasonic “A” scan that was run at specific points on the circuit. The results of the 2011 inspection did not indicate any issues that required corrective action.

NDT results for the piping circuit covering the last 10 years showed no appreciable loss in wall material thickness.

The ultrasonic inspection procedures used to examine the piping circuit may not have been effective in identifying the potential for a weld failure because the procedures were designed to assess the pipe’s thickness and were taken on a smooth surface at some distance away from the weld’s location. In addition, the voluminous scale deposits on the steel surface may have affected the accuracy of the inspection results.

Prior H2S Gas Release on Another Platform in the Point Arguello Unit

On August 3, 1999, at about 2:00 p.m., an 8-inch high pressure gas flowline on Platform Hermosa ruptured, resulting in a sour gas release. The break occurred on the mezzanine deck, about 64 feet above the ocean, downstream of a third-stage discharge scrubber, V-14, and just prior to the glycol contactor inlet, V-16. The drop in pressure activated the automatic safety system on the platform, which shut in oil and gas production. Platform Hidalgo, with pipelines transporting oil and gas to Platform Hermosa, was also shut in.

The released gas had an H2S concentration of about 18,000 ppm. The H2S alarms on Platform Hermosa activated. No one on Platform Hermosa was harmed. No harm to seabirds or other wildlife was observed.

The flowline failed due to internal corrosion, which reduced the wall thickness until it could no longer contain the normal operating pressure. Corrosion was caused by condensed liquid water reacting with H2S gas to form a corrosive acid gas.

Recommendations

Therefore, we recommend that operators:

· Inspect all piping with similar internal exposure, i.e., wet, sour gas where water and deposits can accumulate, and replace if extensive corrosion is identified.

· Review inspection and maintenance programs for piping exposed to sour gas and

· include procedures for identifying localized corrosion problems using radiography or other non-destructive inspection methods where normal ultrasonic inspection may not be effective, such as the areas near welds, reducers, and flanges.

Verify that your Safety and Environmental Management System program adequately addresses the design, inspection, testing and quality assurance of piping exposed to sour gas in order to prevent the buildup of elemental sulfur and to identify and remediate areas of excessive corrosion so that similar releases of H2S gas can be prevented.

Safety Alerts can be found on the following BSEE webpage: http://www.bsee.gov/Regulations-and-Guidance/Safety-Alerts/Safety-Alerts/

Panel Investigation Reports can be found on the following BSEE webpage: http://www.bsee.gov/Inspection-and-Enforcement/Accidents-and-Incidents/Panel-Investigation-Reports/Panel-Investigation-Reports/

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ACCIDENT INVESTIGATION REPORT- APACHE DEEPWATER ALLOWED DISCHARGE OF DRILLING FLUID INTO THE GULF OF MEXICO

ACCIDENT INVESTIGATION REPORT- APACHE DEEPWATER ALLOWED DISCHARGE OF DRILLING FLUID INTO THE GULF OF MEXICO

INVESTIGATION FINDINGS

At approximately 23:00 hours on 23 May 2014, the Diamond Ocean Onyx semi-submersible, moored, drilling rig under contract to Apache Deepwater LLC (Apache) reported an initial loss of 107 barrels (bbl) of 16.9 pounds per gallon (ppg) of synthetic base mud (SBM) during abandonment operations on Well #1 (Bimini Well) permitted at the subsurface location of Garden Banks (GB) Block 213; surface location at GB Block 169. However, after strapping calculations were completed, the SBM discharge amount was revised from 107 bbl to 61 bbl. There were no injuries or property damage during this incident.

Prior to the SBM spill, the mud line from the Mud Pit Room to the auxiliary recirculation line on the Schlumberger Cement Unit had blockage and required cleaning. Several attempts to remove the blockage between Batch Mixing Tank #2 and Cement Unit by flushing with water were unsuccessful; therefore, the line was removed, cleaned out and reinstalled. While cleaning out the line, the two mud line valves were functioned several times but were left in the open position.

At approximately 22:45 hours, the Schlumberger Cementer began mixing cement from Batch Mixing Tank #2 to the Cement Unit Auxiliary Tub. When he began pumping the first 8 bbl of cement, the Diamond Ocean Toolpusher observed that Batch Mixing Tank #2 was over flowing and discovered that SBM was spilling into the Gulf of Mexico. The Diamond Ocean Toolpusher responded by closing the two open valves on the overboard drain line located below the Main Deck at 23:30 hours that prevented any additional SBM discharge.

On Tuesday 27 May 2014, Bureau of Safety & Environmental Enforcement (BSEE) inspectors from the Lafayette District mobilized to the Diamond Ocean Onyx rig located at the surface location of GB Block 169 to conduct an incident investigation. BSEE inspectors met with representatives from Apache, Diamond Ocean and Schlumberger and obtained documentation related to the SBM spill. The Apache Company Man informed BSEE that a total of 61 bbl of SBM was discharged into the Gulf of which approximately 26 bbl consisted of synthetic based oil. Apache reported that the preliminary cause of the SBM spill was attributed to improperly aligned mud line valves on the Schlumberger Cement Unit. The Schlumberger Cement Unit mud line valves were left in the open position that allowed the SBM to overflow from the 50 bbl Batch Mixing Tank #2 and the Cement Unit 15 bbl Auxiliary Tub. The SBM spilled into the secondary containment areas for both vessels, then flowed into drains that lead to the overboard discharge line. Since the overboard discharge line valves were also left in the open position, this provided a conduit for the SBM to spill into the offshore waters.

Incident investigations conducted by Apache and Schlumberger have attributed the probable causes of the SBM spill to the Cement Unit mud line valves that connected the mud line to auxiliary recirculation lines that were left in the open position after cleaning and were not checked to verify their position prior to the cement job.

The contributing causes to the SBM spill identified by Apache and Schlumberger included: 1) the design of the Cement Unit package did not provide the Cementer with a clear view to monitor Batch Mixing Tank #2 nor was it equipped with a device to remotely monitor the fluid level in the tank; 2) inadequate cement unit start-up procedures; 3) the failure to identify risk associated with handling of SBM with the Cement Unit; and 4) the two valves on the rig's overboard discharge line were in the open position during the cement that provided a pathway for the SBM to spill into offshore waters.

LIST THE PROBABLE CAUSE(S) OF ACCIDENT:

LIST THE CONTRIBUTING CAUSE(S) OF ACCIDENT:

The contributing causes to the SBM spill identified by Apache and Schlumberger included:

1) the design of the Cement Unit package did not provide the Cementer with a clear view to monitor Batch Mixing Tank #2 nor was it equipped with a device to remotely monitor the fluid level in the tank;

2) inadequate cement unit start-up procedures;

3) the failure to identify risk associated with handling of SBM with the Cement Unit; and

4) the two valves on the rig's overboard discharge line were in the open position during the cement job and that provided a pathway for the SBM to spill into offshore waters.

SPECIFY VIOLATIONS DIRECTLY OR INDIRECTLY CONTRIBUTING. NARRATIVE:

Based on the incident investigation findings, a G-110 Incident of Non-Compliance was issued to Apache Deepwater, LLC (Apache) on 27 May 2014 to document its failure to protect health, safety, property, and the environment by performing operations in an unsafe and unworkmanlike manner. On 23 May 2014, Apache allowed an unauthorized discharge of 61 bbl of 16.9 ppg SBM into the Gulf of Mexico from open valves on the Cement Unit mud line and the overboard discharge line.