Doel 3 & Tihange 2 - Some Peer-reviewed Scientific Papers & Reports

335

H. Pircher / Hydrogen corrosion of pressure-vesselsteels

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1000 1100 400 500 600 700 800 900 Yietd strength r N/ram 2] Fig. 7. Critical stress for HSCC (tests according to NACE TM-01-77) [5].

depos i ted weld metal . As long as the hardness remained above 300 HV 10, cracking always occurred wi thin the heat -affected zone. Wi thin a range f rom 300 to 230 HV, the hardest st ructure was found to be suscept ible to HSCC only occasional ly. It was only below 230 HV in the HAZ that no HSCC suscept ibi l i ty was noted in spite of high mechanical stress. The aforement ioned tests underscore how to increase the safety of structural designs by the proper select ion of mater ials and welding condi t ions. In conjunc t ion wi th proper welding condi t ions, steels of a low harden- abi l i ty were found to be advantageous. A rel iable pro-

tect ion against stress-induced HSCC is the l imi tat ion of stress appl ied or - - emphasis is placed on this point - - a reduct ion in hydrogen absorpt ion. As a pract ice-related example, a descr ipt ion is given hereinaf ter of damage caused by st ress- induced HSCC. In 1970, in a town wi th no access to the supra-regional gas supply network, four high-pressure gas spheres were set up. The spheres have a di ame t er of roughly 31 and 40 m, using a service pressure of 8.85 and 10.15 bar. They were made f rom a high-st rength f ine-grained structural steel wi th 500 N / mm 2 in yield strength. The plate thickness was 30 and 34 mm. The spheres were

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Hordness HV10mox HAZ Fig. 8. HSCC in welded constant deflection specimens (NACE type TM-01-77 electrolyte) [51.