Material Selection & Corrosion Study for Field Gas Gathering Station (FGGS) at OIL, Assam

The Main Objective of the Study is to carryout corrosion study using the software Predict or Equivalent to summarize the material selection and material performance of the entire facility for various services under different design conditions.

Optimal selection of engineering material for all the Process piping at the facility by taking into account the normal lowest operating temperature, the lowest temperatures during start-up or shutdown, exceptional cool down events, the coldest ambient temperature of the climate at the plant location and the max/design conditions.

To study and select the appropriate material of all process equipment in facility which fulfill the best requirement at various (min/norm/max/design) operating temperature condition.

Baghjan field is having huge amount of Non-Associated Gas (NAG) potential and the expected gas production from this area in 7.5 MMSCMD.  To explore these resources one modular Field Gas Gathering Station (FGGS) having the facilities for production of natural gas is to be created.

The proposed FGGS shall have Non-Associated Gas (NAG) processing facility for 5.0 MMSCMD (2 trains x 2.5 MMSCMD) and provision to feed Associated Gas (AG) of 0.5 MMSCMD along with the NAG to a Glycol based Dehydration facility (5.0 MMSCMD) for achieving water dew point less than or equal to (0) Zero Deg C.

The Facility shall include Production and Test Manifolds, Gas /Condensate/Water Separators, Gas Heaters, Gas Dehydration, Flare system and Effluent Treatment and disposal system along with the required utilities and auxiliary systems. Space provision will be made within the plant to augment its capacity by installing one more train of 2.5 MMSCMD in future.

Following are the activities carried out in Material handling Study.

  1. Input Analysis and Data Validation.
  2. Study the Process description of each unit. In this project the following units are studied.
    • Production and HP Separators
    • Multi-phase Flow Meter
    • Dehydration Unit
    • Fuel gas System
    • Effluent treatment
    • Flare System
    • Closed blow down system
    • Water treatment and supply
    • Instrment Air and nitrogen
    • Contaminated Rain Water system
  3. Study the fluid composition and Laboratory test results.
  4. Based on Design life and Operating conditions (Temperature, Pressure, Fluid composition, Upset and Start-up conditions), choose the material.
  5. An evaluation of all potential degradation mechanisms. API RP 571 is used to identify the degradation mechanisms.
  6. Consideration of additional corrosion control measures and Internal corrosion assessment performed using Electronic Corrosion Engineer (ECE) version 5.7
  7. Experience with materials and corrosion protection methods from conditions with similar corrosivity.
  8. The major Corrosion Damage Mechanisms considered are
    • Oxygen corrosion
    • Erosion Corrosion
    • Galvanic Corrosion
    • External Corrosion
    • External Corrosion Under Pipe Supports
  9. Conformance to applicable material Specifications, Codes and Standards
  10. The final Results summary with Corrosion Control Methods are detailed in Study report