Materials Performance

DEC 2018

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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20 DECEMBER 2018 W W W.MATERIALSPERFORMANCE.COM MATERIAL MATTERS Continued f rom page 19 of the steel selected for use in high sever- ity service reduces its susceptibility to blistering and HIC. Table 2 lists the most commonly used CS material require- ments used in wet H 2 S service based on the service's severity level. Another control measure involves fab- rication guidelines such as heat treat- ment, testing, and inspection. Since hard- ness is the most important contributing factor for SSC mitigation and residual stress reduction is needed to prevent SCC and SOHIC, an effective PW HT (which reduces both hardness and residual stresses) should be determined. Most specif ications and NACE SP0472 5 require equipment in wet H 2 S service to receive a PW HT at a temperature range of 620 °C minimum with a hold time of 1 h per 25 mm of thickness and a minimum of 1 h. A lso, Desai, Murthy, and Shargay add that all cold-formed (>5% strain) components should be stress relieved even when not required by code. To mitigate the risk of caustic SCC, all CS welds and cold-formed (≥5% strain) components in equipment or piping should receive stress relief/PW HT when the caustic concentration and maximum operating temperature exceed the curve shown in Figure 1 of NACE SP0403. 6 The PW HT temperature should be 635 ± 14 °C for a minimum of 1 h, as recommended in NACE SP0403. As with caustic services, Desai, Murthy, and Shargay comment that all CS welds and cold-formed (≥5% strain) components in amine equipment or piping should also receive stress relief/ PW HT at a temperature of 635 ± 14 °C for a minimum of 1 h to mitigate the SCC risk. Ty pical testing and nondestructive examination on completed components include weld deposit hardness testing and wet f luorescent magnetic particle testing. The production weld hardness is usually limited to a maximum of 200 Brinell hardness. For equipment, one hardness test is normally done every 3 m along the weld length on the main seams, with noz- zle and manway welds tested on the pro- cess side (where accessible). For piping, a percentage of welds is generally tested, with the percentage based on the severity of the service. For equipment prone to corrosion attack, Desai, Murthy, and Shargay also recommend developing process or opera- tional controls that are ty pically applied as an integrity operating window (IOW), which is a set of limits that def ines an assortment of variables (i.e., a velocity limit in amine services or temperature limit in caustic service) that can affect a process unit's mechanical integrity and reliability. Damage or failure that is otherwise preventable can occur if a unit is operated outside of its IOW. References 1 J.J. Desai, C. Shargay, A.S. Murthy, "Good Fabrication Stage Practices to Mitigate Risks Associated with Wet H 2 S, Caustic, Amine, C a r b o n a t e C o r r o s i o n a n d C r a c k i n g ," CORROSION 2018, paper no. 10842 (Hous- ton, TX: NACE International, 2018). 2 ASTM A578/A578M–17, "Standard Specifica- tion for Straight-Beam Ultrasonic Examina- tion of Rolled Steel Plates for Special Appli- cations" (West Conshohocken, PA: ASTM, 2017). 3 NACE TM0284-2016, "Evaluation of Pipeline and Pressure Vessel Steels for Resistance to Hydrogen-Induced Cracking" (Houston, TX: NACE, 2016). 4 NACE Publication 8X194, "Materials and Fabrication Practices for New Pressure Ves- sels Used in Wet H 2 S Refinery Service" (Hous- ton, TX: NACE, 2006). 5 NACE SP0472-2015, "Methods and Controls to Prevent In-Service Environmental Crack- ing of Carbon Steel Weldments in Corrosive Petroleum Refining Environments" (Hous- ton, TX: NACE 2015). 6 NACE SP0403-2015, "Avoiding Caustic Stress Corrosion Cracking of Refinery Equipment and Piping" (Houston, TX: NACE, 2015). —K.R. Larsen

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