[ End User Feature ] cooling deprives the weldment from forming the austenite , which is the key reason behind the fracture toughness in a DSS microstructure . 2 From the review of the metallurgical compositions , it was evident that Alloy 2205 , which is a standard grade DSS , has a nitrogen content between 0.14 - 0.20 whereas Alloy 2507 , which is a super DSS , has a higher nitrogen content ( i . e ., 0.24 - 0.2 ) and a better ability to form austenite than standard DSS Alloy 2209 . The API practices and ASME Section-II Part 3 ( A8.49 & A8.52 ) recommend super DSS grade filler wire ( i . e ., ER 2594 ) for the welding of super DSS grades such as Alloy 2507 . The ferrite number of ER 2209 ( which is a standard DSS ) is 54- 60 , whereas for the super DSS grade ER 2594 it ’ s 45-55 . This implies the higher propensity of ER 2209 to retain the dominant ferritic microstructure ( instead of transition to austenite ) that generally results from the presence of nitrogen during the slow cooling of weldment ( s ). 2 In summary , the higher nitrogen content and lower ferrite in the ER 2594 super DSS filler wire ( than standard DSS ) will have enhanced ability to form the austenite and hence the increased toughness of weldment than ER 2209 . Figure 2 shows a schematic of the weld between tube and tube sheet . So , the failure of the weldment ( via cracking ) resulted from several factors ( or their combined effects ) as below :
[ End User Feature ] cooling deprives the weldment from forming the austenite , which is the key reason behind the fracture toughness in a DSS microstructure . 2 From the review of the metallurgical compositions , it was evident that Alloy 2205 , which is a standard grade DSS , has a nitrogen content between 0.14 - 0.20 whereas Alloy 2507 , which is a super DSS , has a higher nitrogen content ( i . e ., 0.24 - 0.2 ) and a better ability to form austenite than standard DSS Alloy 2209 . The API practices and ASME Section-II Part 3 ( A8.49 & A8.52 ) recommend super DSS grade filler wire ( i . e ., ER 2594 ) for the welding of super DSS grades such as Alloy 2507 . The ferrite number of ER 2209 ( which is a standard DSS ) is 54- 60 , whereas for the super DSS grade ER 2594 it ’ s 45-55 . This implies the higher propensity of ER 2209 to retain the dominant ferritic microstructure ( instead of transition to austenite ) that generally results from the presence of nitrogen during the slow cooling of weldment ( s ). 2 In summary , the higher nitrogen content and lower ferrite in the ER 2594 super DSS filler wire ( than standard DSS ) will have enhanced ability to form the austenite and hence the increased toughness of weldment than ER 2209 . Figure 2 shows a schematic of the weld between tube and tube sheet . So , the failure of the weldment ( via cracking ) resulted from several factors ( or their combined effects ) as below :
• High tensile stresses from thermal elongation of tubes , since the SS 316L expansion joints could be incompatible with the Alloy 2507 due to the 22 % higher coefficient of thermal expansion
• The reduced toughness of the weldment due to the reduced austenite caused by the rapid cooling of the weldment
• Internal stresses due to dissimilar welds may have contributed to dissimilar metal weld ( DMW ) cracking 1
• Fatigue failure due to thermal cycling caused by multiple start-up and shutdowns
Summary Under heat transfer conditions , corrosion rates from formic acid are higher than in the non-heat transfer condition . This factor was not accounted for during the material selection for the twin pass heat exchanger in the first place . The cracking that occurred even after the tubes were upgraded to Alloy 2507 stemmed from high tensile stress at the weld-tube sheet junction due to the tube expansion force ( due to dissimilar thermal expansion coefficient ). In addition , internal stresses due to dissimilar welds may have also contributed to dissimilar metal weld ( DMW ) cracking . Finally , fatigue due to thermal cycling was caused by multiple start-ups and shutdowns . The repairs involving dissimilar metals and corrosive service should be accompanied by Engineering reviews .
References
1 . API RP 571 , “ Damage Mechanisms Affecting Fixed Equipment in the Refining Industry ” ( Washington , DC : API , 2020 ).
2 . Immad Ovais Rohela , Ahmad Raza Khan Rana , Yasar Irshad , “ Case Study On The Failure Of Duplex Stainless Steel Heat Exchanger From Thermal Shock ,” AMPP CORROSION 2024 ( Paper No . 20923 ).
EN 1.4835 / UNS S30815 / 253 MA tm
Heat- and creep resistant austenitic stainless steel
EN 1.4835 / UNS S30815 / 253 MA TM is a highly versatile austenitic heat- and creepresistant chromium-nickel steel that offers a unique combination of properties , making it an excellent choice for various high-temperature applications .
Examples of Application
• Metallurgical processes ( e . g ., recuperators in steel mills , PCI lances for blast furnaces )
• Petrochemical plants ( e . g ., pyrolysis vessels , high-temperature piping systems )
• Power generation ( e . g ., boiler nozzles , combustion chambers )
• Industrial furnaces and heat treatment equipment
Stocked Products and Dimensions
Plates on stock in thickness range 1,50 up to include 50,00 mm in size 1500 x 3000 mm . Other sizes available upon request .
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