Ben Martin CA6NM - Class B would be ideal since double tempering gives both reduced hardness and with improved toughness (Impact strength is nearly doubled). With reduced hardness < 200 BHN, chances of SCC due to H2S especially in sour service would be less. or would get extended if H2S content varies in the crude being processed. NACE MR 0103 probably considered this aspect to suggest CA6NM Class B. In sweet service, CA6NM Class A with hardness maintained around 200-210 BHN in single tempered (this means a longer holding time at tempering temp to reduce hardness to this level) may be OK. Since you are planning to use this casting both for sweet and sour services, CA 6 NM Class B would be a better choice from warding-off potential SCC in H2S - as you will not be sure about the crude processed and the varying H2S content being serviced by your customers. At the design stage, gearing for potential problems from better material or heat treatment considerations availability and to save from long term potential trouble shooting problems would be a woth investment. From this angle, CA 6NM Class B would be a better choice. Trust this helps you C.V.Srinivasan Nishi Engineers Pvt Ltd India July 01, 2006 E-mail: nishi@vsnl.com >Hello, > >We've designed a casting out of CA6NM Class A to house a >water-cut sensor to be employed into oil pipe lines. I need >to determine if Class A is suitable versus Class B (Class A >= singe temper, Class B = double temper). We will want to >sell this unit into sweet & sour applications. > >NACE standard MR0103 indicates that a double tempering must >be employed in order to use CA6NM. Can Class A be used >under a certain pH & H2S PPM level? We have used CF8M in >the past with success and I find no mention of this material >as suitable. > >Any help would be appreciated. > >Regards, >Ben Martin