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Exxonmobil Edd 1a- Cui

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  ExxonMobil Proprietary Materials Equipment DegradationDocuments MaintenancePractices Manual CORROSION UNDER INSULATION EDD1APage1 of 10TMEE-062 PROPRIETARY INFORMATION  - For Authorized Company Use OnlyJuly, 2003 ExxonMobil Research and Engineering Company - Fairfax, Virginia DESCRIPTION Corrosion under insulation (CUI) refers to external corrosion of equipment underneath insulation/ jacketing, whichhas allowed the ingress of moisture.CUI of carbon steel and low alloy steel may occur when equipment or piping operates at temperatures between25  F and 300  F (-4  C and 149  C). In general, the metal temperature will be approximately the same as the processtemperature (for insulated equipment). However, if the insulation is damaged and/ or highly humid conditionscommonly exist, a process temperature significantly above 250  F (121  C) can result in metal temperatures lowenough to cause CUI, therefore the CUI range is extended to 300  F (149  C). In addition, equipment subject tocyclic temperatures even outside of this range (e.g., regeneration equipment) should be considered to be subject toCUI. A special form of CUI is chloride SCC of austenitic stainless steel in a marine environment or in case of sprayingwith brackish, or salt (fire) water. Insulation of austenitic stainless steel should be avoided in marine environmentswhen possible. When insulation is required for process reasons, a full thickness protective coating system or wrapped Al foil should be applied if the service temperature is above 150  F (65  C). Chlorides may also be presentin the insulation itself, and can be leached out when wet, leading to SCC. Consideration should be given to the useof expanded metal cages instead of thermal insulation if only required for personnel protection. Chloride SCC of austenitic stainless steel is covered in EDD 9. DATA REQUIREMENTS FOR THE APPLICATION OF THE EDDTable 1A-1.  Information Required to Assess Corrosion Under Insulation Data RequiredExplanation Coating InformationThermal Spray Aluminum (TSA)/Organic Coating/ NoCoating, Age of CoatingExternal EnvironmentMarine, Cooling Tower Drift, Sweating or IndustrialOperating TemperatureEstablish if in CUI range - 25  F to 300  F (-4  C to 149  C).MetallurgyCarbon and low alloy steels, stainless steelsInsulation ConditionGood/ Poor Operating HistoryConstant, variable.Inspection HistoryFrequency, thickness measurements REFERENCES AND BACKGROUND INFORMATION   Recommended Practice for Piping Strategy Development (PIEP)   CUI Detection Strategy & Methods (EE.25E.94)   API Piping Inspection Code API 570, 2nd Edition, October 1998   ER&E Piping Maintenance Guide, TMEE 010, December 1990   Guide to the Inspection of Plant Structures, EETD 0071  ExxonMobil Proprietary Materials Equipment DegradationDocuments MaintenancePractices Manual CORROSION UNDER INSULATION EDD1APage2 of 10TMEE-062 PROPRIETARY INFORMATION  - For Authorized Company Use OnlyJuly, 2003 ExxonMobil Research and Engineering Company - Fairfax, Virginia   CE 16E.82 Thermal Insulation Design, Installation and Inspection to Control CUI   NACE RP0198-98 The Control of Corrosion under Thermal Insulation and Fireproofing Materials A Systems Approach   IP 19-1-1 Paints and Protective Coatings   IP 14-1-1, 14-2-1 External Insulation   EMCC Plant Inspection Manual, Sections 12.4.1 and 15.3.1   ERIM   Steel Structures Painting Manual, Volume 1, Good Painting Practice, and Volume 2, Systems andSpecifications, SSPC, Pittsburgh, PA, USA   AWS/NACE/SSPC Standard Specification for the Application of Thermal Spray Coatings (Metallizing) of  Aluminum, Zinc, and Their Alloys and Composites for the Corrosion Protection of Steel.   Use of Thermal Spray Aluminum for CUI Prevention (2000CENGT2059)   CUI Prevention by Use of Al foil (2001CENGT2059)   Standard Design and Use Guide for Personnel Protection in Place of Insulation (2000CENGT2086) FAILURE / DAMAGE MODES The most common type of failure for CUI is a leak due to external corrosion on the equipment or piping. Becausethe corrosion is hidden, it is difficult to detect. The most susceptible areas are at equipment attachments whichprotrude from the insulation; stiffener rings or insulation support rings that can trap and hold moisture; changes inequipment configuration; small connections and piping with lower nominal thickness; piping operating in the 175 to300  F ( (80  C to 149  C)  range; low spots; known equipment areas that are difficult to coat and near locations whereinsulation damage is evident. Local climate (i.e. high humidity, marine environment) and intermittent operatingtemperatures may aggravate the problem. Table 1A-2.  Corrosion Under Insulation Functional Failure Descriptions Failure Mode DescriptionFunctional Failure DescriptionRCM Failure Pattern Corrosion holeLeakage, External (1) D: Low failure probability when newfollowed by random failures.Notes:(1) High risk or low risk to be determined during equipment strategy development.  ExxonMobil Proprietary Materials Equipment DegradationDocuments MaintenancePractices Manual CORROSION UNDER INSULATION EDD1APage3 of 10TMEE-062 PROPRIETARY INFORMATION  - For Authorized Company Use OnlyJuly, 2003 ExxonMobil Research and Engineering Company - Fairfax, Virginia PROBABILITY ASSESSMENT The following are the unmitigated probabilities of failure as a result of corrosion under insulation. Table 1A-3.  Unmitigated Probability for Leak Due to Corrosion Under Insulation Probability LevelConditions of Degradation  APossibility of Repeated Incidents   Coated and non-coated equipment exposed to severemarine (including salt spray and sea water deluge), severecooling tower drift or sweating environmentsBPossibility of Isolated Incidents   Non-coated equipment exposed to marine, cooling tower drift or sweating environmentsCPossibility to Occur Sometime   Non-coated equipment exposed to industrial environments   TSA coated equipment exposed to marine, cooling tower drift, sweating conditions.   Organic coated equipment exposed to marine, cooling tower drift, sweating conditions or industrial environmentDNot Likely But Possible   TSA coated equipment in industrial environment.EPractically Impossible   Non-coated equipment exposed to dry/arid conditions   TSA and organic coated equipment exposed to dry/aridconditions Notes: If the metal temperature is above 175  F (80  C), consider increasing the probability by 1 level.For small bore piping, piping with lower nominal thickness, or piping that is thin due to corrosion, consider increasing the probability by 1 level.This EDD applies to carbon steel and low alloy steel. It does not apply to copper nickel alloys, titanium alloys or high nickel alloys such as 825, 625, and C-276. See EDD 9 for external SCC of austenitic and duplex stainlesssteels.Site experience has shown that dry/arid environments do not cause CUI. Age Adjustment :Coating age adjustment for full thickness coating systems (may be varied according to site experience) Table 1A-4.  Probability adjustments for full thickness coating systems   ORGANIC COATINGTHERMAL SPRAY ALUMINUMAGE OF COATING (YEARS)FACTORAGE OF COATING (YEARS)FACTOR 0 to 5-20 to 10-25 to 10-110 to 20-1>100>200  ExxonMobil Proprietary Materials Equipment DegradationDocuments MaintenancePractices Manual CORROSION UNDER INSULATION EDD1APage4 of 10TMEE-062 PROPRIETARY INFORMATION  - For Authorized Company Use OnlyJuly, 2003 ExxonMobil Research and Engineering Company - Fairfax, Virginia  Age of uncoated/unprimed carbon steel beneath insulation Table 1A-5.  Probability adjustments for uncoated carbon steel beneath insulation TIME BENEATH INSULATION (YEARS)FACTOR 0 to 5-15 to 100> 10+1 Insulation condition : Table 1A-6.  Probability adjustment based on condition of insulation INSULATION CONDITIONFACTOR Good (Sealed)0Poor (Not sealed, damaged, poor design)with visible potential for CUI+1Clear evidence of CUI (water, heavyscale, rust staining on weather jacketing,etc.)+2 MITIGATION OF RISKInspection Adjustments : Fixed Equipment - Visual InspectionTable 1A-7.  Probability adjustment based on inspection   MAINTENANCE CATEGORYTIME SINCE LAST VISUALINSPECTIONFACTOR MON0 to 10 (non-TSA)0MON>10 to 20 (non-TSA)+1MON>20 (non-TSA)+2MON0 to 20 (TSA ONLY)0MON>20 (TSA ONLY)+1 Note:  When inspection of the organic coating or TSA results in it being in (confirmed/repaired/replaced) goodcondition, then the inspection clock for determining the coating credits is back to the srcinal coated probability. Fixed Equipment - Other Inspection Inspection of organic coated equipment using the techniques below enables a reduction in the probability of up to 3levels as follows, assuming that any damaged areas found are repaired. Inspection scope and follow-uprequirements should be consistent with PIEP documents.- 1 level reduction for 10% inspection effort.-   Up to 3 level reduction for 100% inspection effort.

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Jul 14, 2019
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