Corrosion Attack on FGD Systems
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Corrosion Attack on FGD Systems In 2205 Duplex Stainless Steel Absorber Vessels Corrosion Problems With 2205 There are several material systems (metallic, organic, plas- tics, coating, etc.) available to construct these systems, but due to cost, fabrication, and availability issues, the absorber vessels, tanks, piping, and spray towers in many new installa- tions have been constructed using duplex stainless steel alloy 2205. Unfortunately, many of these newer units are experi- encing severe corrosion attack in operational time windows of three months to three years. The primary mode of corrosion appears to be under- deposit/crevice corrosion and pitting in weld heat-affected zones (HAZ), weld metal and base metal areas of the vessel. Corrosion can be initiated due to surface contamina- tion and surface finish created by the initial fabrica- tion/erection of the component. Some reports suggest this corrosion will extend to other duplex grades such as 255 and standard stainless steels such as Grades Type 316L, 317L, and 317LMN. Figure 1 is a macro-section through an absorber vessel Duplex 2205 horizontal seam weld. Note the corrosion progressing from the heat affected zone to the unaffected base metal. This corrosion attack often results in through-wall leaks. Inspection is Essential Utilities need to inspect limestone-based absorber vessels and components to determine if under-deposit corrosion is active in alloy 2205, other duplex and standard stainless steel alloy vessels, tanks, and spray towers. Inspection is essential to determine the structural integrity of the vessel and compo- nents. Because much of the observed corrosion is under thick deposits of gypsum and hard tenacious scales, the use of proper cleaning procedures, inspection techniques and state-of-the-art nondestructive examination methods are critical to identifying corrosion damage. State-of-the-art flue gas desulfurization (FGD) technologies continue to be installed on most large coal fired electric generating units in response to new regulatory emission requirements. Aggressive corrosion has been noted in some of these systems, presumably from the low pH, high chloride environments created in the FGD process. fig. 1: Cross-section of weld seam
Transcript of Corrosion Attack on FGD Systems
Corrosion Attack on FGD SystemsIn 2205 Duplex Stainless Steel Absorber Vessels
Corrosion Problems With 2205
There are several material systems (metallic, organic, plas-tics, coating, etc.) available to construct these systems, butdue to cost, fabrication, and availability issues, the absorbervessels, tanks, piping, and spray towers in many new installa-tions have been constructed using duplex stainless steel alloy2205. Unfortunately, many of these newer units are experi-encing severe corrosion attack in operational time windows ofthree months to three years.
The primary mode of corrosion appears to be under-deposit/crevice corrosion and pitting in weld heat-affectedzones (HAZ), weld metal and base metal areas of the vessel. Corrosion can be initiated due to surface contamina-tion and surface finish created by the initial fabrica -tion/erection of the component. Some reports suggest thiscorrosion will extend to other duplex grades such as 255 andstandard stainless steels such as Grades Type 316L, 317L,and 317LMN.
Figure 1 is a macro-section through an absorber vessel Duplex2205 horizontal seam weld. Note the corrosion progressingfrom the heat affected zone to the unaffected base metal. This corrosion attack often results in through-wall leaks.
Inspection is Essential
Utilities need to inspect limestone-based absorber vesselsand components to determine if under-deposit corrosion isactive in alloy 2205, other duplex and standard stainless steelalloy vessels, tanks, and spray towers. Inspection is essentialto determine the structural integrity of the vessel and compo-nents. Because much of the observed corrosion is underthick deposits of gypsum and hard tenacious scales, the useof proper cleaning procedures, inspection techniques andstate-of-the-art nondestructive examination methods arecritical to identifying corrosion damage.
State-of-the-art flue gas desulfurization (FGD) technologies continue to be installed on most large coal fired electric generatingunits in response to new regulatory emission requirements.Aggressive corrosion has been noted in some of these systems, presumably from the low pH, high chloride environments created in the FGD process.
fig. 1: Cross-section of weld seam
Figure 2 shows evidence of both heavy and light depositswith corrosion attack. Note the side-by-side juxtaposition of corrosion attack and unaffected area that still have millmarkings.
Costly DowntimeFGD systems are designed to be integral with the boilerand therefore cannot be isolat-ed. A leak in the absorber ves-sel in most power generationstations will require taking theboiler out of service to repairthe leak(s) which is an expen-sive activity, given the cost ofreplacement power. Inspectionof FGD Absorber Vessels maytake up to several weeks using conventional inspectiontechniques such as API 653methods.
In-Service Detection of FGD Absorber Vessel Wall Corrosion DamageBy using a variety of advanced nondestructive testingmeth ods, corrosion attack can be detected from outside the vessel wall while the FGD system remains in service. Thisapproach provides data that can be used to effectively plan:
• Visual inspection,
• Remediation repairs, or
• Fitness for service-/remaining life assessment of theabsorber vessel using FEA generated by the results of theNDE method.
These planning activities can all be accomplished prior to taking the FGD Absorber vessel out of service, therebyreducing downtime.
SES Has the Expertise You NeedStress Engineering Services (SES) is a recognized leader in detecting and assisting utilities in the mitigation ofcorrosion damage in 2205 duplex stainless steel absorbervessels. SES offers a broad range of services, including:
• Metallurgical/corrosion expertise necessary to validate theexistence of corrosion damage
• NDE and Inspection Services for FGD absorber vessel forcorrosion damage
• Fitness for Service and Remaining Life assessments for FGDAbsorber Vessels and components damaged by corrosion
• Mitigation strategies related to corrosion damagedabsorber vessels
For Help ResolvingFGD Corrosion Problems
Call SES Today at 513-336-6701Houston Cincinnati New Orleans Baton Rouge Calgary
ON THE WEB AT WWW.STRESS.COM© 2011 Stress Engineering Services, Inc. 442
fig. 3: Heavy gypsumdeposits in a FGDAbsorber Vessel.
fig. 2: Heavy and light deposits with corrosion attack.
fig. 4: Typical heavy deposits in an Absorber Vessel.
