# Hydrogen Sulfide Hazard

Hydrogen Sulfide is a kind of hazardous, odorless gas which may not only threaten our health and safety, but also pollute the environment and result in serious accidents and economic losses. If hydrogen sulfide is dissolved in water during oilfield development, it will corrode oilfield equipment and pipelines, causing wall thickness to become thinner or corrosive pitting and perforation. There have been many accidents about sudden tear, brittle failure and welding cracking from all over the world during exploration and production of sour oil and gas fields containing hydrogen sulfide, most of them were caused by hydrogen induced crack (HIC) and sulfide stress corrosion cracking(SSCC).

# Source of Hydrogen Sulfide

· Hydrogen-sulfide-containing formation fluid

· Sulfur containing additive decomposition in drilling fluid

· Reaction of sulfur contained in thread lubricant

· Bacteria impact on sulphate in drilling fluid

 

# Hydrogen Sulfide Corrosion Principle

（1） International definition of wet hydrogen sulfide

NACE MR0175 defines wet hydrogen sulfide as follows in stress cracking resistant metallic materials for oilfield equipment :

1）Sour gas system: gas pressure≥0.4MPa and hydrogen sulfide partial pressure ≥0.0003MPa

2）Sour multiple-phase system: If the crude oil contains two-phase or three-phase medium (oil, water and gas), the condition can be broadened to: Total gas pressure≥1.8MPa and hydrogen sulfide partial pressure≥0.0003MPa; Gas pressure ≤1.8MPa and hydrogen sulfide partial pressure ≥0.07MPa; Or gaseous hydrogen sulfide is greater than 15%.

（2）Hydrogen sulfide electrochemical corrosion process

When hydrogen sulfide is exposed to moisture, it will ionize and produce hydrogen atoms which can penetrate into steel and dissolve into lattice and finally form into hydrogen molecular because of affinity. Hydrogen molecular in turn will cause steel lattice structure to deform ,reduce the material toughness and increase the brittleness, crack then will occur and expand due to stress impact, this is called Sulfide Stress Corrosion Cracking.

 

 

 

# Hydrogen Sulfide Corrosion Form

· Hydrogen Blistering, HB

· Hydrogen Induced Cracking, HIC

· Sulfide Stress Corrosion Cracking, SSCC

· Stress Oriented Hydrogen Induced Cracking, SOHIC

 

Corrosion by Hydrogen Sulfide, especially HB, HIC, SSCC, SOHIC is actually the result of a material damage that is caused by the interaction of metal and hydrogen that diffused into it.

 

# Hydrogen Sulfide Corrosion Morphology Features

· Even FeS film

· Sharp bottom at corrosion pit

· Edge corrosion and slightly inclined.

· Side corrosion

 

 

# Hydrogen Sulfide Corrosion Products

· Black and black blue FeS；

· Ferroferric Oxide；

· Sulfur；

· Sulfur Dioxide.

 

# Preventive Measures

· Use conventional low carbon alloy steel with hardness less than or equal to 22HRC in a sour environment.

· Continuously add hydrogen sulfide corrosion inhibitor and sulfur eliminator. Organic and oxygen-containing corrosion inhibitor is recommended such as ammoniac compounds, imidazoline, amides, Q-PECK, sulfur compound and phosphorous compound.

· Keep a detailed record of operational data, the fatigue life of a coiled tubing string should be shorter than expected in a sour environment, therefore, we should diminish the life expectancy of the coiled tubing string based on operational history record.

· Add bactericide and industrial detergent to prevent sulfate-reducing bacteria in well fluid and circulation fluid from producing microbial colony and sulfide which in turn will cause hydrogen sulfide corrosion.

· Conduct a simulation corrosion test before operation, analyze corrosive medium and microbe content in acid pumper and circulation fluid during operation.

· Apply oil to outer surface of the tubing for protection and purge the inside surface after operation. Check possible defects such as mechanical damage, corrosion pit and crack on the outside surface if NDT method is readily available.