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


  • 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.

Sour Scenario as per MR-01-75
Fig. 1: Sour Scenario as per MR-01-75

Limitations of NACE MR-01-75

  • Saltwater wells, injection wells
  • Downstream Industries, Petrochemical
  • Refineries and Chemical plants
  • Low-pressure multiphase systems
READ  Piping Specifications | Piping Material Specification (PMS) | Piping Class

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.

Fig. 3: SOUR SCENARIO – 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!

Dynamics of Sour Environments

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

Dynamics of Sour Environment
Fig. 4: Dynamics of Sour Environment

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

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

5 thoughts on “What is a Sour Service? | NACE Sour Service Criteria

  1. Some of the information you are presenting is out of date or misleading. I strongly recommend to update the content.

  2. Anup, Can there be a scenario in which Water Injection pipeline be in “Sour Service” environment? My understanding is no, as Injection water will not have H2S. Could you clarify. My e-mail is sanjivs@npcc.ae

    1. Yes, Water Injection pipeline can be in “Sour Service” if water is injected from GOSP residual water, like saltwater disposal from GOSP

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