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Nguyen Bich Technical Director CorrOcean Canada, Inc. Calgary, Alberta, Canada

The Battle of Troy Retold in Wet Sour Gas Corrosion Mechanisms

In Greek mythology, as told by Homer's Iliad, Achilles' skin was made impenetrable when Thetis dipped her infant son in the River Styx. His only weak spot was the heel by which she held him. Achilles grew up to be an invincible warrior until the arrow of Paris found that weak spot in the famous Battle of Troy. In the end, the Trojans were defeated after they took in the wooden horse as they thought complete victory was in their hand.

Yes, Virginia, history repeats itself. We have found Achilles' heel and the Trojan Horse in our battle against wet sour gas corrosion.

The Achilles' Heel in Sour Gas Corrosion:

When carbon steel is exposed to wet sour gas, FeS forms and quickly reduces corrosion to a very low level. This protective shield explains why there is practically no corrosion in the vapor phase in wet sour gas pipelines. However, this FeS scale can break down locally, resulting in very severe pitting with rates as high as 30 mm/y. The scale disrupters, the arrows of Paris in sour gas corrosion, are: high chlorides, elemental sulfur, excessive methanol injected for hydrate control, spent acids from well workovers, etc.

Additional Shields for Achilles' Heel:

Achilles could use one of these additional shields (equivalent measures for sour gas corrosion mitigation in parentheses):

• Stayed in Athens instead of going to battle (dehydration to remove water)
• Put strong metal shield around his heel (corrosion resistant alloy)
• Wore tough plastic shoes (non-metallic liners)
  
• Drove the chariot faster (increase flow rate to avoid water stagnation)
  
• Diluted Paris' strength by sending party invitation every night (sulfur solvent)
  
• Avoided alcohol during battle (no excessive methanol injection)
  
• Sprayed simulated River Styx water on his heel every day (corrosion inhibition)
  
• Cleaned and painted his feet with concentrated simulated River Styx water once every few weeks (pigging and batching)

The Trojan Horse:

Corrosion inhibitors are supposed to reduce corrosion! Unfortunately, some inhibitors can actually increase pitting corrosion several folds (versus blanks) if they are under or over dosed. These inhibitors must not be used! Testing inhibitor protection performance at various concentrations can reveal this Trojan horse behavior.

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