Material requirements for resistance to sulfide stress cracking (SSC) in sour refinery process environments (i.e., environments that contain wet hydrogen sulfide [H2S]). AKA "wet H2S cracking".
CORRECTION OF PUBLICATION:
In January 2016, NACE published an incorrect version of ANSI/NACE MR0103/ISO 17945:2015 (Petroleum, petrochemical and natural gas industries — Metallic materials resistant to sulfide stress cracking in corrosive petroleum refining environments). That document was incorrectly titled ANSI/NACE MR0103/ISO 17495:2016. The erroneous standard was retracted at the time and the NACE Store has the corrected version. NOTE: The contents of both versions of the standard are identical. The only discrepancies are in the title.
NACE MR0175/ISO 15156 gives requirements and recommendations for the selection and qualification of carbon and low-alloy steels, corrosion-resistant alloys, and other alloys for service in equipment used in oil and natural gas production and natural gas treatment plants in H2S-containing environments, whose failure could pose a risk to the health and safety of the public and personnel or to the equipment itself.
Residual elements (RE) in carbon steel, not specifically included in the specified steel, appear to influence the corrosion rate under certain conditions, especially in services involving hydrofluoric acid (HF). The relative proportions of RE, specifically %C, %Ni, %Cu, and %Cr in carbon steel base and weld metals used in refineries, especially in alkylation processes with HF as the catalyst, significantly impact corrosion behavior. Studies described in the literature show corrosion damage with high RE (Cu + Ni + Cr >0.20) components as compared to low RE (Cu + Ni + Cr <0.20) components.
In this study, electrochemical corrosion testing was performed on a 3-inch pipe elbow section with high REs that had developed a through-wall leak in service. Test results were compared to those obtained on a similar pipe elbow section with lower REs. The samples were exposed to 50% HF at room temperature and at 65°C. Linear polarization resistance (LPR) corrosion rates were measured at both temperatures. Potentiodynamic (PD) polarization scans were performed on samples of low and high RE steel exposed to 50% HF at room temperature.
Test results indicated that LPR corrosion rates were higher for the high RE carbon steel samples than for low RE carbon steel samples at both temperatures. PD scans showed that the critical current densities were higher for high RE steel than for low RE steel.
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Sulfuric acid (H2SO4) is the largest volume commodity chemical in use today.It plays some part in the production ofnearly all manufactured goods. One large use of concentrated sulfuric acid is used as a catalyst for refinery alkylationunits.Intheseunits,C3-C5olefinssuchaspropyleneorbutylenearereactedwithisobutanetoformgasoline-blendingcomponents such as isoheptane and isooctane.These gasoline-blending components are used to boost octane forautomobileandaviationfuels.
Most refineries have an alkylation unit that uses either hydrofluoric acid (HF) or sulfuric acid as the alkylation catalyst.Thisstandarddealswithspentsulfuricacidassociatedwiththesulfuricacidalkylationprocessonly.
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This standard establishes guidelines to prevent most forms of environmental cracking of weldments in carbon steel refinery equipment, including pressure vessels, heat exchangers, piping, valve bodies, and pump and compressor cases. Weldments are defined to include the weld deposit, base metal HAZ, and adjacent base metal zones subject to residual stresses from welding. It defines standard practices for producing weldments in P-No. 1 steels resistant to environmental cracking in corrosive petroleum refining environments. This standard is maintained by Task Group 326.