Materials Performance

MAY 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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13 NACE INTERNATIONAL: VOL. 56, NO. 5 MATERIALS PERFORMANCE MAY 2017 THE BLOG Continued f rom page 11 up to a lot of "ifs." I am a fan of internally lined pipe with a good epoxy system. In the case of an epoxy-lined pipe, you can use a robot to blast and coat the weld seam. We just finished a 42-in (1.07 m) diameter pipeline with internal epoxy coat- ing. We used a combination of manual and robotic blasting before coating this line. A: I think a positive seal coupling is the best solution for this ty pe of application. It will take the same pressure as a welding joint, is economical, and is easy to install. Cathodic Protection of Type 304L Pipe Q: What are your thoughts or experiences related to cathodic protection (CP) of Ty pe 304L stainless steel (SS) (UNS S30403) pipe in a soil env ironment? At this time, I do not have soil data to share. Any thoughts would be helpful as I am currently evaluating an existing underground pipe system and a defective CP system to determine if CP is actually needed and warrants replacement. A: SS in a soil environment will likely behave just like mild steel in a soil environment, so I would expect the CP to be necessary. is is especially true in chloride-contaminated soils or microbially active soils. A: You do not provide much informa- tion but I will make some comments: • If the soil contains chlorides, there are the attendant risks common to SS. • Depending on the soil characteristics, you need to consider the possibility of microbial effects. • If chlorides are present, there will be the risk of stress corrosion cracking if the line operates at >50 °C. • ere is a prima facie case for applying CP, but this depends on the precise location and operating conditions. • If the line is electrically isolated from other structures, a CP design should be relatively straightforward. • If the line is connected to other structures (e.g., carbon steel pipeline or copper earthing), it becomes a little more complicated. You would be wise to isolate the line if possible. • If the line is not isolated, I would recommend a current drain test. A: I can support this advice about chloride in the soil. We experi- enced leaks caused by external pitting of pipe made of Ty pe 316L SS about four or five months after burial. is was in an area where the soil was contaminated with salt. I would expect Ty pe 304 SS (UNS S30400) in the same environment to corrode at a higher rate than Ty pe 316 SS (UNS S31600). SS obtains its resistance from the pas- sive f ilm that is formed on its surface. In cases where the passive f ilm cannot be replenished (i.e., anaerobic conditions), it is possible for localized corrosion to occur. I would be cautious about using uncoated buried SS. I would prefer external coating and CP as the best combination for protec- tion. Obviously, the same can be achieved using steel, but I assume you need the SS for resistance to the product being conveyed. © 2017 Aegion Corporation Aegion Coating Services, AllSafe, The Bayou Companies, Brinderson, Corrpro, Fibrwrap Construction, Fyfe Co., Insituform, MTC, Schultz, Underground Solutions and United Pipeline Systems 844.619.2926 ARE YOUR ASSETS PROTECTED? PIPELINE INTEGRITY MANAGEMENT: Threat assessments Hazard identification Pipeline surveys Inline inspection Direct assessments Cathodic protection engineering Data management and GIS Pipeline remediation Mitigation and prevention SEE CORRPRO. MP0117

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