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NACE International

Detection, Repair, and Mitigation of Cracking in Refinery Equipment in Wet H2S Environments - Item No. 21078
 N SP0296

Annotation

General

This standard is intended to be a primary source of information on cracking in wet H2S petroleum refinery environments and provides guidelines on the detection, repair, and mitigation of cracking of existing carbon steel refinery equipment in wet H2S environments.

For the purposes of this standard, the term equipment refers to pressure vessels and piping made of carbon steel plate material. Refinery pressure vessels include items such as, but not limited to, columns or towers, heat exchangers, drums, reboilers, and separators.

Limited cracking has been noted in seamless piping; therefore, the information in this standard concentrates on longitudinally seam-welded pipe fabricated from plate.

Information on fabrication and inspection practices for new pressure vessels (never in service) is in NACE Publication 8X194.

For the purposes of this standard, the term wet H2S environments includes, but is not limited to, refinery process environments known to cause wet H2S cracking resulting from hydrogen entry into the steel, as defined in NACE Standard MR0103.4 Some environmental conditions known to cause wet H2S cracking are those containing an aqueous phase and:

(a) > 50 ppmw total sulfide content in the aqueous phase; or

(b) ? 1 ppmw total sulfide content in the aqueous phase and pH < 4; or

(c) ? 1 ppmw total sulfide content and ? 20 ppmw free cyanide in the aqueous phase and pH > 7.6; or

(d) > 0.3 kPa absolute (0.05 psia) partial pressure H2S in the gas phase associated with the aqueous phase of a process. However, the threshold total sulfide content in the aqueous phase required for cracking to occur has not been clearly established. Therefore, selective application of this standard may be appropriate when experience has indicated the presence of cracking or blistering in comparable service, regardless of total sulfide content.