XI.M29 (NUREG-2191 R0)

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XI.M29 OUTDOOR AND LARGE ATMOSPHERIC METALLIC STORAGE TANKS

Program Description

The Outdoor and Large Atmospheric Metallic Storage Tanks aging management program (AMP) manages the effects of loss of material and cracking on the outside and inside surfaces of metallic aboveground tanks constructed on concrete or soil. All metallic outdoor tanks (except fire water storage tank interior surfaces and exterior surfaces not exposed to soil or concrete) and certain indoor metallic tanks are included. If the tank exterior is fully accessible, tank outside surfaces may be inspected under the program for inspection of external surfaces ( Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report AMP XI.M36) for visual inspections of external surfaces recommended in this AMP; surface examinations are conducted in accordance with the recommendations of this AMP. This program credits the standard industry practice of coating or painting the external surfaces of steel tanks as a preventive measure to mitigate corrosion. The program relies on periodic inspections to monitor degradation of the protective paint or coating. Tank inside surfaces are inspected by visual or surface examinations as required to detect applicable aging effects.

For storage tanks supported on earthen or concrete foundations, thickness measurements of the tank bottom are conducted because corrosion could occur at inaccessible locations.


Evaluation and Technical Basis

1. Scope of Program: Tanks within the scope of this program include: (a) all metallic outdoor tanks (except fire water storage tank interior surfaces and exterior surfaces not exposed to soil or concrete) constructed on soil or concrete; (b) indoor large volume metallic storage tanks (i.e., those with a capacity greater than 100,000 gallons) designed to internal pressures approximating atmospheric pressure and exposed internally to water; and (c) other indoor metallic tanks that sit on, or are embedded in concrete where plant-specific operating experience reveals that the tank bottom (or sides for embedded tanks) to concrete interface is periodically exposed to moisture. If the tank exterior is fully accessible, tank outside surfaces may be inspected under the program for inspection of external surfaces ( GALL-SLR Report AMP XI.M36). Aging effects for fire water storage tank interior surfaces and exterior surfaces not exposed to soil or concrete are managed using GALL-SLR Report AMP XI.M27. Visual inspections are conducted on tank insulation and jacketing when these are installed.
This program may be used to manage the aging effects for coatings/linings that are applied to the internal surfaces of components included in the scope of this program as long as the following are met:
2. Preventive Actions: In accordance with industry practice, steel tanks may be coated with protective paint or coating to mitigate corrosion by protecting the external surface of the tank from environmental exposure. For outdoor tanks, sealant or caulking is applied at the interface between the tank external surface and concrete or earthen surface (e.g., foundation, tank interface joint in a partially encased tank) to mitigate corrosion of the tank by minimizing the amount of water and moisture penetrating the interface. Certain tank configurations may minimize the amount of water and moisture penetrating these interfaces by design, (e.g., foundation is sloped in a manner that prevents water from accumulating).
3. Parameters Monitored or Inspected: The program consists of periodic inspections of metallic tanks (with or without coatings) to manage the effects of corrosion and cracking on the intended function of these tanks. Inspections cover all surfaces of the tank (i.e., outside uninsulated surfaces, outside insulated surfaces, bottom, interior surfaces). The AMP uses periodic plant inspections to monitor degradation of coatings, sealants, and caulking because it is a condition directly related to the potential loss of material or cracking. Thickness measurements of the bottoms of the tanks are conducted periodically. Periodic internal visual inspections and surface examinations, as required to detect applicable aging effects, are performed to detect degradation that could be occurring on the inside of the tank. Where the exterior surface is insulated for outdoor tanks and indoor tanks operated below the dew point, a representative sample of the insulation is periodically removed or inspected to detect the potential for loss of material or cracking underneath the insulation, unless it is demonstrated that the aging effect [i.e., stress corrosion cracking (SCC), loss of material] is not applicable, see Table XI.M29-1, “Tank Inspection Recommendations.”
4. Detection of Aging Effects: Tank inspections are conducted in accordance with Table XI.M29-1 and the associated table notes. Degradation of an exterior metallic surface can occur in the presence of moisture; therefore, periodic visual inspections at each outage are conducted to confirm that the paint, coating, sealant, and caulking are intact. The visual inspections of sealant and caulking are supplemented with physical manipulation to detect degradation. If the exterior surface is not coated, visual inspections of the tank’s surface are conducted within sufficient proximity (e.g., distance, angle of observation) to detect loss of material. If the tank is insulated, the inspections include locations where potential leakage past the insulation could be accumulating.
When necessary to detect cracking in materials susceptible to cracking such as stainless steel, and aluminum, the program includes surface examinations. When surface examinations are required to detect an aging effect, the program states how many surface examinations will be conducted, the area covered by each examination, and how examination sites will be selected.
If the exterior surface of an outdoor tank or indoor tank exposed to condensation (because the in-scope component being operated below the dew point) is insulated, sufficient insulation is removed to determine the condition of the exterior surface of the tank, unless it is demonstrated that the aging effect (i.e., SCC, loss of material) is not applicable, see Table XI.M29-1, “Tank Inspection Recommendations.” When an aging effect requires management, periodic inspections are conducted. During each 10-year period of the subsequent period of extended operation, remove a minimum of either 25 one-square foot sections or 20 percent of the tank insulation and perform inspection of the exposed exterior surface of the tank. Aging effects associated with corrosion under insulation for outdoor tanks may be managed by GALL-SLR Report AMP XI.M36, “External Surfaces Monitoring of Mechanical Components.”
The sample inspection points are distributed in such a way that inspections occur on the tank dome (if it is flat), near the bottom, at points where structural supports, pipe, or instrument nozzles penetrate the insulation and where water could collect such as on top of stiffening rings. In addition, inspection locations are based on the likelihood of corrosion under insulation occurring (e.g., given how often a potential inspection location is subject to alternate wetting and drying in environments where trace contaminants could be present, how long a system at a potential inspection location operates below the dew point).
Alternatives to Removing Insulation:
  1. Subsequent inspections may consist of examination of the exterior surface of the insulation for indications of damage to the jacketing or protective outer layer of the insulation when the results of the initial inspection meet the following criteria:
    1. No loss of material due to general, pitting or crevice corrosion, beyond that which could have been present during initial construction is observed, and
    2. No evidence of SCC is observed.

    If the external visual inspections of the insulation reveal damage to the exterior surface of the insulation or jacketing, or there is evidence of water intrusion through the insulation (e.g., water seepage through insulation seams/joints), periodic inspections under the insulation continue as conducted for the initial inspection.

  2. Removal of tightly adhering insulation that is impermeable to moisture is not required unless there is evidence of damage to the moisture barrier. If the moisture barrier is intact, the likelihood of corrosion under insulation is low for tightly adhering insulation. Tightly adhering insulation is considered to be a separate population from the remainder of insulation installed on in-scope components. The entire population of in-scope tanks that have tightly adhering insulation is visually inspected for damage to the moisture barrier with the same frequency as for other types of insulation inspections. These inspections are not credited towards the inspection quantities for other types of insulation.
Potential loss of material and cracking of tank bottoms is determined from volumetric inspections of the tank bottoms that are performed whenever the tank is drained or at intervals not less than those recommended in Table XI.M29-1.
When inspections are conducted on a sampling basis, subsequent inspections are conducted in different locations unless the program states the basis for why repeated inspections will be conducted in the same location.
Inspections and tests are performed by personnel qualified in accordance with site procedures and programs to perform the specified task. Inspections and tests within the scope of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) follow procedures consistent with the ASME code. Non-ASME Code inspections and tests follow site procedures that include inspection parameters for items such as lighting, distance, offset, surface coverage, presence of protective coatings, and cleaning processes.
Table XI.M29-1. Tank Inspection Recommendations1, 2
Inspections to Identify Degradation of Inside Surfaces of Tank Shell, Roof4, and Bottom5, 6
Material Environment Aging Effect
Requiring
Management
(AERM) 		Inspection
Technique3 		Inspection Frequency
Steel Air,
condensation 		Loss of
material 		Visual from
inside
surface (IS)
or
Volumetric
from
outside
surface
(OS)7 		Each 10-year period starting 10 years
before the subsequent period of
extended operation
Raw water,
waste water 		Loss of
material 		Each 10-year period starting 10 years
before the subsequent period of
extended operation
Treated water Loss of
material 		One-time inspection conducted in
accordance with GALL-SLR Report
AMP XI.M328
Stainless
steel8 		Air,
condensation 		Loss of
material 		Visual Each refueling outage interval or
one-time inspection, see SRP-SLR
Sections 3.2.2.2.2, 3.3.2.2.4, or
3.4.2.2.3.
Cracking Surface11 Each 10-year period starting 10 years
before the subsequent period of
extended operation, or one-time
inspection, see SRP-SLR Sections
3.2.2.2.4, 3.3.2.2.3, or 3.4.2.2.2.
Raw water,
waste water 		Loss of
material 		Visual Each 10-year period starting 10 years
before the subsequent period of
extended operation
Treated water,
treated borated
water 		Loss of
material 		Visual from
IS or
Volumetric
from OS7 		One-time inspection conducted in
accordance with GALL-SLR Report
AMP XI.M328
Aluminum Air,
condensation 		Loss of
material 		Visual Each 10-year period starting 10 years
before the subsequent period of
extended operation, or one-time
inspection, see SRP-SLR Sections
3.2.2.2.10, 3.3.2.2.10, or 3.4.2.2.9.
Cracking Surface11 Each 10-year period starting 10 years
before the subsequent period of
extended operation, or demonstrate
that SCC is not an applicable aging
effect, see SRP-SLR Sections
3.2.2.2.8, 3.3.2.2.8, or 3.4.2.2.7.
Treated water,
treated borated
water 		Loss of
material 		Visual from
IS or
Volumetric
from OS7 		One-time inspection conducted in
accordance with GALL-SLR Report
AMP XI.M328
Raw water,
waste water 		Loss of
material 		Visual Each 10-year period starting 10 years
before the subsequent period of
extended operation, or one-time
inspection, see SRP-SLR Sections
3.2.2.2.10, 3.3.2.2.10, or 3.4.2.2.9.
Cracking Surface11 Each 10-year period starting 10 years
before the subsequent period of
extended operation, or demonstrate
that SCC is not an applicable aging
effect, see SRP-SLR Sections
3.2.2.2.8, 3.3.2.2.8, or 3.4.2.2.7.
Inspections to Identify Degradation of External Surfaces9 of Tank Shell, Roof, and Bottom
Material Environment AERM Inspection
Technique3 		Inspection Frequency
Steel Air – indoor
uncontrolled
Air – outdoor 		Loss of
material 		Visual from
OS 		Each refueling outage interval
Soil, concrete Loss of
material 		Volumetric
from IS12 		Each 10-year period starting 10 years
before the subsequent period of
extended operation13
Stainless
Steel 		Air,
condensation 		Loss of
material 		Visual from
OS 		Each refueling outage interval or
one-time inspection, see SRP-SLR
Sections 3.2.2.2.2, 3.3.2.2.4, or
3.4.2.2.3.
Cracking Surface11 Each 10-year period starting 10 years
before the subsequent period of
extended operation or one-time
inspection, see SRP-SLR Sections
3.2.2.2.4, 3.3.2.2.3, or 3.4.2.2.2.
Soil, concrete Loss of
material 		Volumetric
from IS12 		Each 10-year period starting 10 years
before the subsequent period of
extended operation13
Cracking Volumetric
from IS12 		Each 10-year period starting 10 years
before the subsequent period of
extended operation13
Aluminum Air,
condensation 		Cracking Surface11 Each 10-year period starting 10 years
before the subsequent period of
extended operation or demonstrate that
SCC is not an applicable aging effect,
see SRP-SLR Sections 3.2.2.2.8,
3.3.2.2.8, or 3.4.2.2.7.
Loss of
material 		Visual from
OS 		Each 10-year period starting 10 years
before the subsequent period of
extended operation, or one-time
inspection, see SRP-SLR Sections
3.2.2.2.10, 3.3.2.2.10, or 3.4.2.2.9.
Soil, concrete Cracking Volumetric
from IS12 		Each 10-year period starting 10 years
before the subsequent period of
extended operation13
Loss of
material 		Volumetric
from IS12 		Each 10-year period starting 10 years
before the subsequent period of
extended operation13 or demonstrate
that SCC is not an applicable aging
effect, see SRP-SLR Sections
3.2.2.2.8, 3.3.2.2.8, or 3.4.2.2.7.

  1. GALL-SLR Report AMP XI.M30, “Fuel Oil Chemistry,” is used to manage loss of material on the internal surfaces of fuel oil storage tanks. However, for outdoor fuel oil storage tanks exposed to soil or concrete and indoor tanks exposed to periodically wetted concrete or exposed to soil, inspections to identify aging of the external surfaces of tanks are conducted in accordance with GALL-SLR Report AMP XI.M29. GALL-SLR Report AMP XI.M41 is used to manage loss of material and cracking for the external surfaces of buried tanks.
  2. When one-time internal inspections in accordance with these footnotes are used in lieu of periodic inspections, the one-time inspection must occur within the 5-year period before the start of the subsequent period of extended operation.
  3. Alternative inspection methods may be used to inspect both surfaces (i.e., internal, external) or the opposite surface (e.g., inspecting the internal surfaces for loss of material from the external surface, inspecting for corrosion under external insulation from the internal surfaces of the tank) as long as the method has been demonstrated to be effective at detecting the AERM and a sufficient amount of the surface is inspected to provide reasonable assurance that localized aging effects are detected. For example, in some cases, subject to being demonstrated effective by the applicant, the low frequency electromagnetic technique (LFET) can be used to scan an entire surface of a tank. If follow-up ultrasonic examinations are conducted in any areas where the wall thickness is below nominal, an LFET inspection can effectively detect loss of material in the tank shell, roof, or bottom.
  4. Nonwetted surfaces on the inside of a tank (e.g., roof, surfaces above the normal waterline) are inspected in the same manner as the wetted surfaces based on the material, environment, and AERM.
  5. Visual inspections to identify degradation of the inside surfaces of tank shell, roof, and bottom cover all the inside surfaces. Where this is not possible because of the tank’s configuration (e.g., tanks with floating covers or bladders), the SLRA includes a justification for how aging effects will be detected before the loss of the tank’s intended function.
  6. For tank configurations in which deleterious materials could accumulate on the tank bottom (e.g., sediment, silt), the internal inspections of the tank’s bottom include inspections of the side wall of the tank up to the top of the sludge-affected region.
  7. At least 20 percent of the tank’s internal surface is to be inspected using a method capable of precisely determining wall thickness. The inspection method is capable of detecting both general and pitting corrosion and be demonstrated effective by the applicant.
  8. At least one tank for each material and environment combination is inspected at each site. The tank inspection can be credited towards the sample population for GALL-SLR Report AMP XI.M32.
  9. For insulated tanks, the external inspections of tank surfaces that are insulated are conducted in accordance with the sampling recommendations in this AMP. If the initial inspections meet the criteria described in the preceding “Alternatives to Removing Insulation” portion of this AMP, subsequent inspections may consist of external visual inspections of the jacketing in lieu of surface examinations. Tanks with tightly adhering insulation may use the “Alternatives to Removing Insulation” portion of this AMP for initial and all follow-on inspections.
  10. Not used.
  11. A minimum of either 25 sections of the tank’s surface (e.g., 1-square-foot sections for tank surfaces, 1-linear-foot sections of weld length) or 20 percent of the tank’s surface are examined. The sample inspection points are distributed in such a way that inspections occur in those areas most susceptible to degradation (e.g., areas where contaminants could collect, inlet and outlet nozzles, welds).
  12. When volumetric examinations of the tank bottom cannot be conducted because the tank is coated, an exception is stated, and the accompanying justification for not conducting inspections includes the considerations in footnote 13, below, or propose an alternative examination methodology.
  13. A one-time inspection conducted in accordance with GALL-SLR Report AMP XI.M32 may be conducted in lieu of periodic inspections if an evaluation conducted before the subsequent period of extended operation and during each 10-year period during the subsequent period of extended operation demonstrates that the soil under the tank is not corrosive using actual soil samples that are analyzed for each individual parameter (e.g., resistivity, pH, redox potential, sulfides, sulfates, moisture) and overall soil corrosivity. The evaluation includes soil sampling from underneath the tank. Alternatively, a one-time inspection conducted in accordance with GALL-SLR Report AMP XI.M32 may be conducted in lieu of periodic inspections if the bottom of the tank has been cathodically protected in such a way that the availability and effectiveness criteria of GALL-SLR Report AMP XI.M41, ‘Buried and Underground Piping and Tanks’,” Table XI.M41-3., “Inspections of Buried Tanks for all Inspection Periods,” have been met beginning 5 years prior to the subsequent period of extended operation, and the criteria continue to be met throughout the subsequent period of extended operation.
5. Monitoring and Trending: The effects of corrosion of the tank surfaces are detectable by visual and surface (for cracking) examination techniques. Based on operating experience (OE), periodic inspections provide for timely detection of aging effects. Where practical, identified degradation is projected until the next scheduled inspection. Results are evaluated against acceptance criteria to confirm that the timing of subsequent inspections will maintain the components’ intended functions throughout the subsequent period of extended operation based on the projected rate of degradation.
6. Acceptance Criteria: Any degradation of paints or coatings (cracking, flaking, or peeling), or evidence of corrosion is reported and requires further evaluation to determine whether repair or replacement of the paints or coatings should be conducted. Non-pliable, cracked, or missing sealant and caulking is unacceptable. When degraded sealant or caulking is detected, an evaluation is conducted to determine the need to conduct follow up examination of the tank’s surfaces. Indications of cracking are analyzed in accordance with the applicable design requirements for the tank. Ultrasonic testing (UT) thickness measurements of the tank bottom are evaluated against the design thickness and corrosion allowance.
7. Corrective Actions: Results that do not meet the acceptance criteria are addressed in the applicant’s corrective action program under those specific portions of the quality assurance (QA) program that are used to meet Criterion XVI, “Corrective Action,” of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the corrective actions element of this AMP for both safety-related and nonsafety-related structures and components (SCs) within the scope of this program.
Flaws in the caulking or sealant are repaired and follow-up examination of the tank’s surfaces is conducted if deemed appropriate.
Additional inspections are conducted if one of the inspections does not meet acceptance criteria due to current or projected degradation (i.e., trending). The number of increased inspections is determined in accordance with the site’s corrective action process; however:
  • For inspections where only one tank of a material, environment, and aging effect was inspected, all tanks in that grouping are inspected.
  • For other sampling-based inspections (e.g., 20 percent, 25 locations) the smaller of five additional inspections or 20 percent of the inspection population is conducted. If subsequent inspections do not meet acceptance criteria, an extent of condition and extent of cause is conducted to determine the further extent of inspection. At multi-unit sites, the additional inspections include inspections at all of the units with the same material, environment, and aging effect combination.
The timing of the additional inspections is based on the severity of the degradation identified and is commensurate with the potential for loss of intended function. However, with the exception of external visual inspections of tanks without insulation, the additional inspections are completed within the interval in which the original inspection was conducted or, if identified in the latter half of the current inspection interval, within the first half of the next inspection interval. These additional inspections conducted in the next inspection interval cannot also be credited towards the number of inspections in the latter interval. External visual inspections when the tank is not insulated are conducted within the original refueling outage interval.
If any projected inspection results will not meet acceptance criteria prior to the next scheduled inspection, inspection frequencies are adjusted as determined by the site’s corrective action program. However, for one-time inspections that do not meet acceptance criteria, inspections are subsequently conducted at least at 10-year inspection intervals.
8. Confirmation Process: The confirmation process is addressed through those specific portions of the QA program that are used to meet Criterion XVI, “Corrective Action,” of 10 CFR Part 50, Appendix B. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the confirmation process element of this AMP for both safety-related and nonsafety-related SCs within the scope of this program.
9. Administrative Controls: Administrative controls are addressed through the QA program that is used to meet the requirements of 10 CFR Part 50, Appendix B, associated with managing the effects of aging. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the administrative controls element of this AMP for both safety-related and nonsafety-related SCs within the scope of this program.
10. Operating Experience: A review of OE reveals that there have been instances involving defects variously described as wall thinning, pinhole leaks, cracks, and through-wall flaws in tanks. In addition, internal blistering, delamination of coatings, rust stains, and holidays have been found on the bottom of tanks.
The review of plant-specific OE during the development of this program is to be broad and detailed enough to detect instances of aging effects that have occurred repeatedly. In some instances, repeatedly occurring aging effects (i.e., recurring internal corrosion) might result in augmented aging management activities. Further evaluation aging management review line items in SRP-SLR Sections 3.2.2.2.7, 3.3.2.2.7, and 3.4.2.2.6, “Loss of Material Due to Recurring Internal Corrosion,” include criteria to determine whether recurring internal corrosion is occurring and recommendations related to augmenting aging management activities.
The program is informed and enhanced when necessary through the systematic and ongoing review of both plant-specific and industry OE including research and development such that the effectiveness of the AMP is evaluated consistent with the discussion in Appendix B of the GALL-SLR Report.


References

10 CFR Part 50, Appendix B, “Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants.” Washington, DC: U.S. Nuclear Regulatory Commission. 2016.

US NRC. Information Notice 2013-18, “Refueling Water Storage Tank Degradation.” Agencywide Documents Access and Management System (ADAMS) Accession No. ML13128A118. Washington, DC: U.S. Nuclear Regulatory Commission. September 13, 2013.

Aging Management Program

Final Safety Analysis Report

Stress Corrosion Cracking

American Society of Mechanical Engineers

Generic Aging Lessons Learned - The US NRC GALL Report is NUREG-1801. The US NRC Subsequent License Renewal GALL is NUREG-2191

Subsequent License Renewal - The extension of the original license from 40 years to 60 years is known as License Renewal. Extensions of the license beyond 60 years are known as Subsequent License Renewal.

Subsequent License Renewal Application - The document submitted by the plant licensee under 10 CFR 54 to extend the operating license of the plant beyond 60 years in 20 year increments. 10 CR 54 has no limits on the number of license extensions that can be approved for a plant.

Operating Experience

Ultrasonic Test - A nondestructive test method using ultrasonic waves to determine the thickness of a component and to detect cracks or other degradation.

Quality Assurance

United States of America

Nuclear Regulatory Commission - The US federal government agency that regulates nuclear power plants

Agency wide Documents Access and Management System - The official recordkeeping system, through which the U.S. Nuclear Regulatory Commission (US NRC) provides access to the "libraries" or collections of publicly available documents

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