What is a Sour Service? | NACE Sour Service Criteria

What is a Sour Environment?

NACE defines a Sour environment as one that contains enough H₂S either in the gaseous or aqueous media.

Properties of Hydrogen Sulphide

• Chemical Formula: H₂S
• Odour: Rotten Egg
• Boiling point: 60OC
• Specific Gravity: 1.19
• Odour level: 0.13 mg/kg

The fatality of Hydrogen Sulphide (mg/kg)

• Respiratory breakdown: 100
• Nerve paralysis: 150
• Nausea, Dizziness: 200
• Unconsciousness: 500
• Asphyxiant, Fatal: 700

What is Sour Service?

Sour Service is defined as a fluid service containing water as liquid & H₂S exceeding the limits defined below:

Sour Gas-

Sour Gas Service is defined as the gas service

IF            the Total Pressure of the gas being handled is > = 65 PSIA

AND       Partial Pressure of H₂S in the gas is > 0.05 PSIA

Then      The Environment is SOUR Gas

Sour Oil and Multi-phase

IF            the Fluid handled is Crude or Crude+Water+Gas

AND

• Gas to Oil Ratio > 5000 (SCF/bbl)
• H₂S content in Gas-phase > 15%
• Partial Pressure of H₂S in Gas Phase > 10 PSIA
• Surface operating Pressure > 265 PSIA

Then     The Environment is SOUR Oil

Sour Scenario in the oil industry as per NACE MR-01-75

Refer to the below image (Fig. 1) which shows a curve segregating the sour and non-sour regions as per NACE MR-01-75. The curve denotes the amount of H₂S requirement for qualification of being Sour at a given absolute pressure.

Limitations of NACE MR-01-75

• Saltwater wells, injection wells
• Downstream Industries, Petrochemical
• Refineries and Chemical plants
• Low-pressure multiphase systems

HIC Scenario – API Nelson Curves

Refer to Fig. 2 which shows the HIC and Non-HIC regions.

Sour Scenario as per ISO 15156 / EFC 16

Fig. 3 shows the sour service criteria as per ISO 15156/EFC 16.

Sour Service H₂S ppm Criteria as per DEP

Shell DEP provides the following H₂S criteria for fluid services

• 0 to 49 PPM: Sweet Service
• 0 to 499 PPM: Low-Risk Sour Service
• 500 + PPM: High-Risk Sour Service

Hydrogen Sulphide – What it Can Do!

• Hydrogen- Hydrogen Induced Cracking (HIC)
• Sulphide- Sulphide Stress Cracking (SSC)

Dynamics of Sour Environments

Fig. 4 shows the dynamics of the sour service environment.

For more understanding of NACE Services, I suggest the following course: NACE CIP 1 practice exam