Mitigation Strategy Selection by Environment and Material
What the exam expects
Mitigation must match the mechanism, the environment, and the material. Candidates must know the main options and their limits:
- Chemical inhibition: film-forming inhibitors for CO2/H2S; biocides for MIC; oxygen scavengers for oxygen ingress. Dose, availability, and compatibility matter.
- Material selection: carbon steel with corrosion allowance; CRAs (13Cr, duplex, nickel alloys) for severe service; non-metallics with temperature and permeation limits.
- Coatings and linings: internal coatings for low-severity service; limitations at high temperature and in abrasive flow.
- Process control: dehydration, pH adjustment, velocity management, and removal of oxygen.
Traps in questions
- Choosing an inhibitor for a mechanism it does not address (e.g., biocide for CO2 corrosion).
- Assuming CRA is immune; it can suffer pitting, chloride stress cracking, and sour service limits.
- Ignoring inhibitor availability and compatibility with other chemicals.
- Forgetting that coatings fail and need inspection.
Worked example
A sour wet gas line with high chlorides and moderate temperature is proposed for 13Cr. The correct caution is that 13Cr has chloride and sour-service limits, so a duplex or nickel alloy may be required depending on partial pressure and temperature. Rule of thumb: select mitigation by mechanism first, then check material limits against the specific environment.