NORSOK M-506 CO2 corrosion rate calculation model on public enquiry

NORSOK M-506, Edition 3, June 2016 is now ready for industrial enquiry, with the deadline for comments 2016-09-15. This edition will, when approved and published, replace NORSOK M-506 Rev. 2, June 2005. All comments must be submit through "Standards for enquiry".

NORSOK standard M-506 presents a recommended practice for calculation of corrosion rates in hydrocarbon production and process systems where the corrosive agent is CO2.

The standard contains:

  • A computer program for corrosion rate calculations
  • A user manual for the computer program. A description of the calculation model, the algorithms and the conditions for the corrosion rate calculations are given. In additions, methods and algorithms for calculation of essential input parameters to the corrosion rate, calculations are given.

The corrosion rate equations included in NORSOK M-506 describe the calculation model that shall apply, while the computer program itself is an optional aid that the users of the model may apply such that they possess an efficient tool to conduct corrosion rate calculations and parameter studies. This computer program is developed based on the corrosion rate model given as equations in the standard.

Changes from previous edition
In the present Edition 3, the following changes have been made compared to Revision 2, June 2005:

4. Included that the model is not applicable when the H2S partial pressure is higher than 0.05 bar, or when the ratio between the partial pressure of CO2 and H2S is less than 20. The model can lead to underprediction of the corrosion rate when the total content of organic acids exceeds 100 ppm and the CO2 partial pressure is less than 0.5 bar, particularly in condensing systems. This is changed from Rev. 2, where the H2S partial pressure limit was set to 0.5 bar in the computer program for corrosion rate calculations.

4. Removed the use of corrosion inhibitor efficiency. Included reference with advice on practical use of the corrosion prediction model.

5.2. Included a warning that the model may be less conserative around 90 °C than at other temperatures.

5.3. / 7.1. Removed effect of corrosion inhibitors. Removed inhibitor efficiency as input parameter in Table 3.

7.2.2. Replaced "formation water" with "produced water". Replaced "Bicarbonate" with "Total alkalinity" in Table 6. Included "Acetic acid + Acetate" as new input parameter in Table 6.

8.1. Included a warning that the fugacity calculation is uncertain at total pressures above 250 bar.

8.2.1. Included description of calculation of pH in presence of organic acids.

8.2.2. Included equation for acetic acid dissociation and description of chemical reactions involving acetic acid.

8.2.3. Included equation for the dissociation constant for acetic acid.

In addition to these changes, some typographical errors have been corrected. A database function has also been included in the computer program, enabling simultaneous calculation for a large number of cases.

Deadline for comments is 2016-09-15.

Contact person at Standards Norway is Espen Holm (link)

Document (link to “Standards for enquiry”)
Calculation model (link to page where the Excel file can be downloaded)

Sist oppdatert: 2016-07-15