Ivan Gutierrez discusses what conditions should be used for calculating H₂S partial pressure when considering sour service.

What is NACE MR0175 intent when it comes to H₂S partial pressure? operating or design pressure to be used in the calculations?

The partial pressure of H₂S (ppH₂S ) is used throughout ANSI/NACE MR0175/ISO 15156 to set the production environment limits for carbon steels, low alloy steels and corrosion resistant alloys. However, NACE MR0175 does not specify if the user should consider operation pressure, design pressure or an intermediate value. So, what is NACE MR0175 intent when it comes to H₂S partial pressure? operating or design pressure to be used in the calculations? Here, OGC Energy addresses these questions.

First, we have to define the partial pressure of H2S (ppH2S ) which is calculated as:

                 ppH2S = system total absolute pressure x mol fraction of H2S present

Is the system total absolute pressure the design or the operating pressure? This is one of the most  frequently asked questions and this video clarifies if design or operating pressure should be used.

At OGC Energy we help clients to determine the partial pressure of H₂S. We have the expertise to help you decide if you should use the operating or design pressure. We do this by evaluating the production conditions (pressure, temperature, produced water etc.), the design and evaluating the risks and consequences. We are here to help you with sour service materials selection and partial pressure calculations.

Talk to our team to today!