Dear Zamani, The problem encountered by you needs little more investigation rather than believing on the Hardness values. Please take this consideartion that the pipeline is already in service for more than 3 years and there are other forms of attacks which would not be reflected through the hardness measurement. wet H2S attack on the steel can be produced by two reasons. 1. Stress related. 2. Corrosion related. Stress related attacks can be controlled through the stress relieving which can be assured through the hardness measurement. Latest norms for the hardness values are 18 HRC and not the 22 HRC as indicated by you. As a confirmation you can expose the weld joints and conduct the hardness measurement there which would give some indication on the pipeline stress relieving history. Corrosion related deterioration are controlled by the material quality, chemical composition and material processing/mill treatment conditions and shall be ensured through the material certificates at the time of commissioning. The following points shall be investigated for the material suitability. 1. HIC test as per NACE-TM-0284 2. Mill treatment 3. Sulphur and Phosphorous content 4. Carbon equivalance. Please let me know your feed back on this topic. Regards, Shabbar Hussain Refinery Corrosion Engineer

Dear Zamani, For the wet H2S services the refineries normally define materials as the Nace severity levels 1 and 2 based on the H2S content. 200 ppm of H2S with the free presence of water makes the condition as NACE severity level-2 and that requires the limitation on the chemical composition and the testing requirements. API-5l Grade-B would gurantee only the chemical composition, it would not gurantee the additional requirements about the chemical stringency.There are other conditions which are also applicable like welding consumables limitation of the Ni content. This is the priliminary assessment of the situation and just the hardness measurements would not certify the pipeline fit for further application. Hardness requirements of 18HRC would definetly assure you against the SSC but other forms of corrosion damages like HIC, blistering and SOHIC would not be determined. The remaing answers about the MR-175 regarding the API-5L Gr-B will be given later. Do write to me . Regards, Shabbar Hussain Refinery Corrosion Engineer.