314351315 Corrosion Control Dowmant Naphlha Hydrotraalm Ini?en Issue: Rm The Corrosion Control Document for the Naphtha Hydrotreater Issued to: Will Guckenburg 03E George Hanson Operations Chuck Bowers - Inspection Mike Petker - Inspection Page 563918 [105593 314251315 Corrosion Gonch Document Naphtha Hydrometer Tescro Northwest Companv initial Issue: Revision #0 accordance with the Basic Practice and Guideline entitled "Inspection for High-Temperature Hydrogen Attack? [Reference Regular inspection is necessary to: - Con?rm that operating conditions are being controlled Within acceptable limits 0 Demonstrate that temperature monitoring and control instrumentation are adequately placed and maintained - Con?rm that temperature control algorithms are adequate - Determine whether HTHA is occurring and/or monitor the progress of HTHA in equipment opera?ng at or near to parameter limits. are nonnally designed so that equipment operates below the Nelson curve. with a margin of or larger to allow for normal small variations in conditions without unduly risking Hr HA damage. However. in many older units. operation of the reactors and heat exchangers up to the HTHA limits is economically attractive. in those units. the approach used to avoid or limit additional HTHA is very close control and monitoring of operating conditions, coupled with frequent inspection. Brief exposure of equipment to conditions above the corresponding Nelson curve will normally not result in immediate HTHA damage. HTHA is preceded by an incubation period during which no change in mechanical properties can be detected- This incubation period varies with the type of steel and severity of exposure, lasting only a few hours under extreme conditions and becoming progressively longer at lower temperature and pressures. Small inadvertent exceedances of hydrogen partial pressure or temperature limits may be acceptable for short periods. but advice should be sought from the materials and conusion specialist. 4.1.6 Sul?dic Corrosion Selection of Cr-Mo steels and Fe-Cr-Ni alloys is the predominant method of limiting sul?dic corrosion in both hydrogen-free oil streams and in Hers containing environments in the temperature range of 500 - The "modi?ed McConomy Curves? are used to select materials for equipment operating in hydrogen-free process streams (inctuding heater tubes when metal temperatures are used). and the ?Couper-Gorman Curves' are used for equipment in hydrogen-containing streams. Both are found in the ASM Metals Handbook, Vol. 13 ?Corrosicn' [Reference Additional guidance on selection for environments is given in the Basic Practice Guideline ?Metals and Alloy Selection for Resistance to Sui?dation in High Temperature Gases? [Reference - When using austean stainleSS steels to resist sulfldic conosion. consideration should be given to their susceptibility to poiythionic acid stress corrosion cracking. 39 Page 563956 005535 - 53 Llo