Optimised steel plates for HIC resistance

The Technical Background

Wet hydrogen sulphide (H2S) cracking in steel has been a problem in petroleum refining and upstream oil and gas processing since the 1950s. As more fields rich in H2S are exploited, and this is increasingly the case, the problem is increasingly significant for equipment fabricated in potentially sensitive carbon-manganese (C-Mn) steels.

Steel in contact with water containing H2S will corrode producing hydrogen at its surface. H2S not only inhibits the formation of hydrogen gas, so reducing the opportunity for it to escape, but promotes its absorption in to the steel. At typical working temperatures below 200 degrees Celsius hydrogen atoms can become trapped causing embrittlement and ultimately cracking.

H2S is responsible for numerous types of problems in steels including hydrogen induced cracking (HIC), sulphide stress cracking (SSC), and stress oriented hydrogen induced cracking (SOHIC). In order to provide better H2S resistance the properties of C-Mn steels have been progressively developed to improve chemistry, cleanliness, homogeneity, and microstructure.

CarElso HIC Premium+

Industeel, a subsidiary of Arcelor Mittal Group, specialises in advanced technology carbon steel, alloy, and stainless steel plates and supplies high H2S-resistant pressure vessel steel plates under its CarElso brand name. In order to facilitate product specification and procurement it has refined, fine-tuned, and optimised its offer under the brand name CarElso HIC Premium+.

Industeel’s steel making includes vacuum ladle refining after electric arc furnace melting of selected scrap enabling the making of very high quality C-Mn steel . Soft-reduction continuous casting or ingot casting under argon protection with optimised mould shape controls solidification conditions and limits the occurrence of segregation. The resulting steel features:

• Very low sulphur (S<=0.001%), oxygen (O<0.0015%), and phosphorus (P<=0.008%, typically 0.006%)
• Controlled chemical composition with optimised alloying guaranteeing low carbon equivalent (CEq) values while maintaining all required mechanical characteristics (typical CEq range is 0.38 to 0.45 depending on thickness and delivery conditions).
• Very low inclusion content

At the final stage of fabrication proper post weld heat treatment (PWHT) of the equipment is strongly recommended. CarElso HIC Premium+ manufactured as C-Mn normalised pressure vessel grades, typically according to ASTM A516 or ASME SA516, requires PWHT in the range 595 to 610 degrees Celcius and this is completely sufficient to achieve the proper mechanical properties, hardness levels, and H2S resistance.

Hydrogen induced cracking is of such significance that numerous material specifications have been developed by oil companies and engineering companies. CarElso HIC Premium+ is designed so that it is compatible with the most stringent of these including Petrobras N1706, Saudi Aramco 01-SAMSS-016, EEMUA 179, Axens IN-43, Shell MESC 74/125, Shell DEP 31.22.10.32, etc.

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