HCL Corrosion (General and localized corrosion).pptx

HCL Corrosion.pptx

1. HCL Corrosion

2. Description General and localized corrosion Dew point corrosion in which vapors condense (containing HCL) from the overhead stream (distillation, fractionation, or stripping tower) The first water droplets that condense can be highly acidic (low pH) and promote high corrosion rates.

3. Affected Material All common materials of construction used in refineries.

4. Critical Factor Primary Factor: HCl Concentration (HCL↑ CR ↑) Temperature (T↑ CR ↑) Alloy composition (PREN) CS and low-alloy steels  no pH <4,5 HCL can form under deposit (Nh4Cl or amine hydrochloride salts) and the deposit can absorb water. 300 SS and 400 SS are not resistance Alloy 400, titanium, and some other nickel-based alloys are better. Titanium performs well in oxidizing conditions but fails rapidly in dry HCl service. The presence of oxidizing agents (oxygen, ferric and cupric ions) will increase the corrosion rate, particularly for Alloy 400 and Alloy B-2

5. Critical Factor Crude Unit: Atmospheric tower overhead system Exchanger shells Tubes and header boxes Cold dead-legs Vacuum ejector and condensing equipment (top of the vacuum tower) Hydroprocessing units: Organic or Inorganic Cl in HC, recycle H2 and create HCl NH4CL salts can form in various parts of the unit, including the effluent side of the hot feed/effluent exchangers because both NH3 and HCl are present and they may condense with water in the effluent train. HCl -containing streams can migrate through the fractionation section, resulting in severe acid dew point corrosion at the mixing point where the stream contacts water

6. Critical Factor Reforming Unit: Chlorides may be stripped from catalyst (effluent train, regeneration system, stabilizer tower, debutanizer tower, and feed/preheat exchangers) HCl -containing vapors can migrate to the gas plant fractionation section, resulting in corrosion at mix points where HCl -containing vapor streams mix with streams containing free water. HCl corrosion can also occur in these streams where they cool below the acid dew point and in water boots and lines off the water boots.

7. Affected Unit or Equipment CS & LAS  uniform thinning, localized corrosion, or under-deposit attack. 300 SS & 400 SS  pitting attack 300 series SS may experience Cl− SCC if the temperature is sufficiently high.

8. Damage Morphology CS & LAS  general thinning, localized corrosion, or under-deposit attack. 300 SS & 400 SS  pitting attack 300 series SS may experience Cl− SCC if the temperature is sufficiently high.

9. Mitigation Crude Unit Maximizing oil tank water separation & crude desalting. Cl < 20ppm on overhead accumulator. Upgrade CS to Ni based alloy and Titanium (for Titanium make sure there is no oxidizing agent) Water wash (dilute the condensing HCL) Caustic injection (D/S desalter). It shall be use carefully to avoid caustic SCC and fouling in the feed preheat train. Various combinations (ammonia, neutralizing amines, and filming amines) injected in the atmospheric tower overhead line before the water dew point. Create Monitoring locations (chloride content, water injection rates, and chemical injection rates) are important for managing HCl corrosion.

10. Mitigation Hydroprocessing Carryover of water and chloride salts, including neutralizing amine hydrochloride salts, should be minimized. HCl in H2 streams should be minimized (e.g. by installing scrubbers or guard beds to remove HCl from hydrogen produced in catalytic reforming units). If necessary, nickel-based alloys can be used. Monitoring locations of HCL are important

11. Mitigation Catalytic reforming Minimizing water and/or oxygenates in the feed will reduce stripping of chlorides from the catalyst. Water washing the hydrocarbon stream to remove the highly water-soluble chlorides Special adsorbents in chloride beds and chloride treaters (from recycle hydrogen streams and from liquid hydrocarbon streams) Monitoring locations of HCL are important

12. Inspection and Monitoring VT UT mapping (AUT) RT (Transition component  elbows, three-way or four-way fittings, and dead-legs). CC and Probe pH checking (boot of the atmospheric tower overhead accumulator) Cl and iron content (The water draws from fractionator and stripper tower overhead drums in hydroprocessing and catalytic reformer units should also be checked regularly)