standard for management of 240-60238156 - national … for management of ... fossil fired power...

PCM Reference : 240-53458931 (Power Plant Turbine Engineering)

SCOT Study Committee Number/Name : Materials and Welding

Standard Technology

Title: Standard for Management of Flow Accelerated Corrosion in Fossil Fired Power Plant

Unique Identifier: 240-60238156

Alternative Reference Number: GPL 36-951

Area of Applicability: Engineering

Documentation Type: Standard

Revision: 2

Total Pages: 12

Next Review Date: December 2020

Disclosure Classification: CONTROLLED DISCLOSURE

Compiled by Approved by Authorised by

………………………………….. ………………………………….. …………………………………..

K. Northcott

Senior Consultant Corrosion

M. Maroga

Materials, Welding and NDT Chairperson

K. Sukhnandan

Manager: Turbine Plant CoE (Acting)

Date: …………………………… Date: …………………………… Date: ……………………………

Supported by SCOT/SC/TC

…………………………………..

T. Mathe

SCOT TC Chairperson

Date: ……………………………

Standard for Management of Flow Accelerated Corrosion in

Fossil Fired Power Plant

CONTROLLED DISCLOSURE

When downloaded from the EDMS, this document is uncontrolled and the responsibility rests with the user to ensure it is in line with the authorised version on the system.


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CONTENTS

Page

1. INTRODUCTION ...................................................................................................................................................... 3

1.1 OBJECTIVES .................................................................................................................................................... 3

2. SUPPORTING CLAUSES ........................................................................................................................................ 3

2.1 SCOPE .............................................................................................................................................................. 3 2.1.1 Purpose ..................................................................................................................................................... 3 2.1.2 Applicability................................................................................................................................................ 3

2.2 NORMATIVE/INFORMATIVE REFERENCES .................................................................................................. 4 2.2.1 Normative .................................................................................................................................................. 4 2.2.2 Informative ................................................................................................................................................. 4

2.3 DEFINITIONS .................................................................................................................................................... 4 2.3.1 Classification ............................................................................................................................................. 4

2.4 ABBREVIATIONS .............................................................................................................................................. 5 2.5 ROLES AND RESPONSIBILITIES .................................................................................................................... 5

2.5.1 Technology Function Responsibility .......................................................................................................... 5 2.5.2 Business Unit Responsibility ..................................................................................................................... 6

2.6 PROCESS FOR MONITORING ........................................................................................................................ 7 2.7 RELATED/SUPPORTING DOCUMENTS ......................................................................................................... 7

3. STANDARD FOR MANAGEMENT OF FAC AND EROSIVE ATTACK ................................................................. 7

3.1 DEVELOPMENT OF A STATION-SPECIFIC FAC PROGRAMME .................................................................. 7 3.2 DEVELOPMENT OF A STATION-SPECIFIC FAC PROCEDURE/WORKS INSTRUCTION .......................... 8

3.2.2 Cycle Chemistry Review and Optimisation ............................................................................................... 8 3.2.3 Scope of Work Compilation & Inspection .................................................................................................. 9 3.2.4 Baseline Inspection ................................................................................................................................... 9 3.2.5 Execution of FAC inspections ................................................................................................................. 10 3.2.6 Decision-making basis ............................................................................................................................ 10 3.2.7 Post-Outage Recommendations ............................................................................................................. 10 3.2.8 Preventive actions to mitigate FAC at new power stations ..................................................................... 11

3.3 RECORDS ....................................................................................................................................................... 11

4. AUTHORISATION .................................................................................................................................................. 11

5. REVISIONS ............................................................................................................................................................ 12

6. DEVELOPMENT TEAM ......................................................................................................................................... 12

7. ACKNOWLEDGEMENTS ...................................................................................................................................... 12






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1. INTRODUCTION

Flow Accelerated Corrosion (FAC) is a failure mechanism that has caused piping and tubing failures, several resulting in injuries and even fatalities, in fossil fired and nuclear power stations over the years.

Single-phase FAC is associated with reducing conditions and may therefore be controlled by optimising the applied feedwater chemistry treatment, e.g. AVT(O) or OT. Single-phase FAC is most likely to occur in economiser inlet tubing and piping to the economiser inlet header, piping around the Boiler Feed Pump, Feedwater and Condensate systems.

Two-phase FAC may occur in all feedwater chemistry regimes. Areas of FAC damage are visually easily observed and characterised, in the case of AVT(O) and OT, as black stripes or patches contrasted against a red-salmon pink protective oxide layer. It typically occurs where a fluid enters a vessel and the difference in temperature and pressure between the entering fluid and the bulk fluid results in flashing with a resultant turbulent two-phase environment.

Two phase FAC locations with the greatest incidence of damage are Deaerator shells followed by high pressure drains, particularly following the level control valve when there is a large temperature and pressure differential between the source (feedwater heater) and destination (another heater or the Condenser) of the drains.

The colour of surfaces offer a semi-accurate indicator of the local chemistry environment during service, thus confirming whether single-phase FAC could occur. When the observed colour in Deaerators is different than suggested by the feedwater chemistry results, action should be taken to investigate and improve chemistry surveillance capabilities.

1.1 OBJECTIVES

This Standard aims primarily to greatly reduce the risk of injury/fatality/equipment damage arising from a consequential leak or a rupture occurring as a result of FAC or Erosive Attack.

The secondary objective is to reduce the amount of corrosion product being transported to the Boiler and Turbine as a result of FAC.

2. SUPPORTING CLAUSES

2.1 SCOPE

2.1.1 Purpose

This Standard provides the strategy for the management of FAC and wall thinning, detailing the methodology and responsibilities required to achieve world class performance in the reduction of this failure mechanism and its associated impacts.

2.1.2 Applicability

Systems and locations that are susceptible to FAC in Eskom fossil power plants include all carbon steel systems and components in the feedwater/boiler circuit that convey water and water/steam mixtures where temperatures are below 300ºC. The FAC Guideline [1] describes in detail the typical locations of both single and two-phase to be considered in fossil power plants.

This document shall apply throughout all divisions of Eskom Holdings (SOC) Limited.






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2.2 NORMATIVE/INFORMATIVE REFERENCES

Parties using this document shall apply the most recent edition of the documents listed in the following paragraphs.

2.2.1 Normative

[1] 240-60238419: Guideline for Detection and Management of Flow Accelerated Corrosion in Fossil Fired Power Plant

[2] Guidelines for Controlling Flow Accelerated Corrosion in Fossil and Combined Cycle Plants, EPRI, Palo Alto, CA: 2005. 1008082

[3] Level I FAC Assessments –

http://hyperwave.eskom.co.za/0x936e3246_0x02617fd4

[4] Outage & FAC SOW/Inspection Tracking Tool -

http://hyperwave.eskom.co.za/0x936e3246_0x02715ec0

[5] 240-55864811: Chemistry for Coal Fired Units with Drum Boilers Operating at 17 MPa and Above Standard

[6] 240-55864800: Chemistry for Coal Fired Units with Drum Boilers Operating at 12 MPa Standard

[7] 240-55864792: Chemistry for Coal Fired Units with Once Through Boilers Operating at 17MPa Standard

[8] 240-92944687: Standard for Performing Digital Radiography for Screening of FAC and Erosive Attack in Fossil Fired Power Plants

2.2.2 Informative

None

2.3 DEFINITIONS

Definition Description

Flow Accelerated Corrosion Dissolution of protective internal oxide on surface of pipes and tubes resulting in corrosion of material and loss of wall thickness.

2.3.1 Classification

a. Controlled Disclosure: Controlled Disclosure to External Parties (enforced by law, or discretionary).

http://hyperwave.eskom.co.za/0x936e3246_0x02617fd4

http://hyperwave.eskom.co.za/0x936e3246_0x02715ec0






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2.4 ABBREVIATIONS

Abbreviation Description

AVT(O) All Volatile Treatment (Oxidising)

BU Business Unit

CV Control Valve

DRT Digital Radiographic Testing

ECM Engineering Change Management (process)

EPRI Electric Power Research Institute

FAC Flow Accelerated Corrosion

Gx Generation

OT Oxygenated Treatment

RTS Return to Service

SM Senior Manager

UT Ultrasonic Testing

2.5 ROLES AND RESPONSIBILITIES

The compilation and authorisation of this Standard signifies top level management support and commitment to the corporate FAC Programme. At this level management recognises the need to provide adequate planned maintenance interventions and funding to implement corrective actions.

2.5.1 Technology Function Responsibility

The Technology function has the responsibility to:

Establish and provide FAC training programmes;

Perform periodic reviews of the Business Unit (BU) FAC Programmes as an assurance function;

Collate, review and present Gx FAC statistics based on data and information provided by BUs;

Provide technology transfer e.g. by arranging seminars;

Ensure that all new designs incorporate appropriate FAC mitigation and control aspects;

Perform periodic revision of related governance documents;

Provide technical support to the BU’s, including:

o Failure analysis and mechanism confirmation; o Component life management including assistance in determining Initial Thickness and

Measured Wear, determining Acceptable Wall Thickness, determining Maximum Wear Rate and determining Remaining Service Life;

o Repair and replacement considerations such as welding, material certification review and confirmation.






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2.5.2 Business Unit Responsibility

1. The Power Station Manager shall be responsible and accountable for ensuring implementation of this standard.

2. The responsibility for the implementation of this standard resides with the Power Station Engineering Manager.

Specific management responsibilities include:

Constituting a multidisciplinary team, led by the Engineering Manager or appointed delegate, including members from all necessary departments and engineering functions and disciplines;

Identification of the position (Custodian) that has overall responsibility for the FAC Programme at each plant;

Developing a station-specific FAC Procedure/Works Instruction which is aligned to meeting the requirements of the Standard and Guideline [1], approved and sponsored by the senior management at the station and RT&D;

Provision of adequate resources, staff, equipment funding and organisational capabilities to enable execution of the FAC programme as per these requirements and the advisory recommendations contained in the Guideline;

Providing the means to ensure that assigned personnel are familiar with the Standard and Guideline [1] documents;

Ensuring that sufficient stock levels of replacement components and materials are available (whether “high chromium” or like for like material) prior to a planned outage opportunity.

Supporting the exchange of information and experience with other sites through participation in the appropriate technical forums.

The responsibility for the review and approval of SOW documents resides solely with the Power Station Engineering Manager with support from the Turbine Plant Engineering, Boiler Plant Engineering, Chemical Services, Operating, Maintenance, Outage and Project Management Managers.

Ensuring implementation of recommendations of all previous metallurgical report/s for the particular unit in terms of actions for inspection or replacement as well as the timelines associated with these recommendations.

3. The Custodian shall have the responsibility to:

Schedule formal FAC team meetings;

Ensure alignment of outage Scopes of Work with station (Outage Department) requirements and timelines before a scheduled outage;

Ensure that the appropriate NDT techniques are applied;

Ensure that appropriate quality control is applied during maintenance and inspection activities;

Ensure submission of the “FAC Inspection Report” documents i.e. spreadsheet, with all parameter and inspection data correctly and suitably populated, to RT&D within a month after outage inspection/replacement activities. Conclusion and issue of the subsequent metallurgical evaluation report is required within a month after submission;

Ensure submission of the next outage Scopes of Work to RT&D, no more than 3 months after the unit RTS;






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Ensure that replacement of high risk areas identified prior to an outage are performed at the earliest available opportunity;

Ensure that no material/line modifications are performed without following the ECM process.

Ensure that the component-specific inspection sheets and images are appropriately archived at the particular site via official site documentation management processes, i.e. Document Management Centre and/or electronic media storage such as Hyperwave, to ensure traceability and future retrieval for audit purposes;

Ensure that the plant information and outage Scopes of Work are continually updated;

Ensure that plant chemistry specifications are adhered to, with appropriate review of reported versus required operating parameters to ensure timely correction of deviations.

2.6 PROCESS FOR MONITORING

The site FAC team shall meet formally at least twice a year, before the outage period to discuss scope of work, and after the outage period to discuss the findings and action plans. The terms of reference for this meeting will be compiled and the proceedings appropriately documented.

2.7 RELATED/SUPPORTING DOCUMENTS

Throughout this document, references to the Standard for Management of FAC, Guideline for Detection and Management of FAC [1] and the station-specific FAC Procedure/Works Instruction will be referred to as the Standard, Guideline and Procedure/Works Instruction.

3. STANDARD FOR MANAGEMENT OF FAC AND EROSIVE ATTACK

It is the Eskom standard to implement an FAC Management Programme at each power station, including the formulation of short, medium and long term strategies for the reduction of FAC (including Erosive Attack).

3.1 DEVELOPMENT OF A STATION-SPECIFIC FAC PROGRAMME

Systems and locations that are susceptible to FAC and Erosive Attack in Eskom fossil power plants include all carbon steel systems and components in the feedwater/boiler circuit. It is therefore crucial that all necessary departments and engineering functions and disciplines are involved in the FAC Management Programme. It is mandatory that a multidisciplinary team, led by the Engineering Manager or appointed delegate, consisting of members from all necessary departments and engineering functions and disciplines, shall be constituted.

The purpose of this team is to develop a comprehensive FAC programme, which includes both inspection-based and cycle chemistry-based activities and the implementation of action plans to address FAC damage. This team shall meet formally at least twice a year:

- before the outage period to discuss scope of work;

- after the outage period to discuss the findings and action plans.

The Terms of Reference for these meetings will be compiled and the proceedings appropriately documented and stored.






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3.2 DEVELOPMENT OF A STATION-SPECIFIC FAC PROCEDURE/WORKS INSTRUCTION

Each power station shall develop a station-specific FAC Procedure/Works Instruction.

In addition to the requirements described in 2.5, this Procedure/Works Instruction shall address the following elements:

Ensuring that the team comprises members as defined in 3.1;

Identification of the position (Custodian) that has overall responsibility for the FAC programme;

Defining the roles, responsibilities and corresponding authority of the various sections dealing with different aspects of FAC (Station Management, Outage Management, Operations, Maintenance, Boiler Engineering, Turbine Engineering and Chemical Services) at the station;

Include representation on the Corporate level (NDE, metallurgists, feedwater specialists, chemists and piping engineers);

Listing the requirements of formal FAC team meetings;

Ensuring that assigned personnel are formally appointed;

Ensuring that the assigned personnel are familiar with the Standard and Guideline [1];

Timeous identification and maintaining of sufficient stock of material for the replacement of high risk areas;

Developing a long-term plan and the identification of long-term goals and strategies for reducing high FAC wear rates i.e. possible material replacement strategies,

Ensuring that high priority replacements are performed at the earliest opportunity.

3.2.2 Cycle Chemistry Review and Optimisation

Each power station shall implement the following minimum requirements:

A baseline study shall be conducted that shall review and document the historical records of feedwater treatment applied and chemistry control achieved on each unit. The elements to be reviewed shall include the type of chemistry regime applied with timelines, the conditioning chemicals applied including concentrations and injection points, the venting practices for the Deaerator and Heaters, trends of chemistry parameters such as Particulate Iron, pH, Dissolved Oxygen and Cation Conductivity, air ingress into the Condensate and Feedwater systems, etc.

The station shall select and apply the most appropriate cycle chemistry regime, based on the materials in the Condenser, Condensate and Feedwater systems, as defined in the Chemistry Standards, 240-55864811 [5], 240-55864800 [6] and 240-55864792 [7], and shall ensure strict compliance with the minimum chemistry surveillance requirements and limits set in the Chemistry Standards.

The station shall ensure that all conditioning chemicals such as Ammonia, pure Oxygen, Carbohydrazide and Amines, are dosed in the appropriate locations and that the dosing systems are automated to ensure optimum chemistry control.

All Eskom units operating with the Oxygenated Treatment and All Volatile Treatment (Oxidising) chemistry regime shall operate their HP Heaters with vents closed during normal operation in order to reduce single- and, to a lesser extent, two-phase FAC in Heater shells and Heater distillate drain lines.

Generation stations on AVT(R) will continue to operate with the HP and LP heater vents opened at all times.






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The rate of corrosion in the cycle shall be monitored by measuring Particulate Iron levels at the Economiser Inlet and at the HP & LP Heater distillate drains, as a minimum, using an on-line corrosion product sampler. Results shall be interpreted in conjunction with other parameters such as pH, Dissolved Oxygen and Cation Conductivity, and physical parameters such as flows, temperatures and pressures, to determine the extent of FAC.

The station shall ensure that the cycle chemistry is periodically reviewed and optimised.

3.2.3 Scope of Work Compilation & Inspection

Generic Scope of Work documents have been compiled for all fossil sites, which include the review of all susceptible systems (FAC and Erosive Attack), design data (isometric drawings in conjunction with plant heat balance diagrams and flow diagrams), operational parameters, drawings and materials experience.

It is mandatory that the sites continue to update information with respect to:

Systems deemed to be low risk in terms of FAC and/or Erosive Attack and therefore excluded from inspection;

In cases where Cycle Chemistry Parameter Excursions have and continue to take place in the Feedwater systems then single-phase locations cannot be excluded from future inspection.

Population of missing information, such as piping dimensional information and piping/component material composition;

The Generic Scope of Work to accurately reflect the status of component material replacement where chromium containing materials have been used.

The Guideline [1] shall be consulted with respect to system susceptibility to FAC and Erosive Attack mechanisms such as cavitation erosion, liquid impingement erosion, etc.

It is strongly recommended that replacement of high risk areas with chromium material, as described in the Guideline [1] i.e. carbon steel expanders immediately preceding the level control valve and all piping components downstream of Control Valves (CV) be considered in preference to inspection. Such replacement will deactivate the FAC mechanism, thereby obviating the need for regular future inspection. In this regard the station will be required to follow the “Plant engineering change management (ECM) process” with due consideration of the impact on the design base, welding issues, financial benefit (cost of replacement versus cost avoidance associated with future inspection) and scheduling of replacements factoring in possibly long lead times.

3.2.4 Baseline Inspection

The first comprehensive FAC inspection, as defined in the Level I FAC Assessment [3], shall be carried out during the first opportunity after commencing plant operation. Thereafter, inspections during every General Overall shall be based on risks as identified during the first FAC inspection.

It is recommended that the outage Scope of Work should include the following, as far as is practical, in conjunction with the recommendations in the Level I FAC Assessment documents:

Always include visual inspection of control valve internals and areas upstream and downstream of each valve during valve maintenance opportunities;

Always include visual inspection of Deaerator, HP & LP heater shells and flashboxes;

Surfaces near cascading drain line entry connections in both LP and HP heaters;

Plant areas susceptible to mechanisms other than FAC, such as erosion attack mechanisms.






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3.2.5 Execution of FAC inspections

Where possible, NDT screening techniques, as described in the Guideline [1], shall be used for initial detection of wall thinning.

The initial NDE inspection shall typically employ either direct visual or remote visual methods i.e. fiberscope and/or camera systems. NDT screening by DRT, as described in [8] can be performed while the unit is running and without the need to remove insulation.

Thinned or damaged areas, determined by NDT screening techniques i.e. visual means, shall receive a second phase inspection by Ultrasonic Testing (UT) to quantitatively determine thickness. Depending upon the results, it may be necessary to expand the initial inspection sample in a particular line or train by performing additional inspections. Follow-up inspection of areas with thinning (if not immediately replaced) shall be planned to evaluate remaining life and eventual repair/replacement activity. It is therefore essential that inspections are scheduled to commence at the earliest opportunity during outages to prevent unnecessary start-up delays, should further work be required.

It is the responsibility of the FAC Custodian to ensure that the appropriate NDT techniques are applied and that appropriate quality control is applied, as per the recommendations and advisory notes in Appendix D of the Guideline [1].

In the case where a component is removed and replaced due to excessive wall thinning, the removed component shall be retained and submitted to the appropriate RT&D specialist for metallurgical (failure) investigation for mechanism confirmation. Components which fail during operation shall also be submitted for failure mechanism confirmation.

3.2.6 Decision-making basis

To enable effective decision making between immediate repairs/replacement OR future management based on remaining WT, FAC rate and time to next inspection, consider the following information:

The “% of Wall Thickness” (as determined by UT) column in the SOW template document provides three level acceptance criteria, as described in the Guideline [1].

Patch or temporary repairs by welding or other sealing methods (e.g. Furmaniting) are not recommended. A temporary weld repair can only be considered in emergency situations as described in the Guideline [1].

3.2.7 Post-Outage Recommendations

The FAC Custodian is required to ensure correctly populated “Inspection Results” field and “Action” columns in the SOW Template (as described in the Guideline [1]) and availability of all supporting inspection reports and images. This shall constitute the FAC Inspection Report.

It is crucial that the relevant specialists and station multi-disciplinary team consider the outage and post-outage results, conclusions and recommendations with respect to:

Future inspection and investigation requirements;

Possible plant modifications;

It is strongly recommended that when material replacement is adopted as the strategy for high risk FAC locations that the replacement material shall be with high chromium material - all replacements shall be made with Cr >1.25% material (including weld repairs). It is imperative that spare material is available for opportunity replacement.

The last two bulleted items shall follow the ECM process.






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3.2.8 Preventive actions to mitigate FAC at new power stations

Actions to mitigate FAC shall be incorporated into the user requirement specifications, design, fabrication, erection, commissioning, operation and maintenance of new power stations.

3.3 RECORDS

It is mandatory that the power station maintain and update the “Generic Scope of Work” document with respect to incomplete information, such as dimensional and material composition, as well as systems not deemed as high risk areas. The “Generic Scope of Work” document shall be updated with historic inspection data for consideration during future inspection Scope of Work compilations;

The Outage & FAC SOW/Inspection Tracking Tool [4] will be used to monitor progress with respect to the SOW and inspection process. Documentation will only be regarded as approved once signed off and published on Hyperwave;

It is the responsibility of the FAC Custodian to ensure that the submission of the outage Scopes of Work are aligned with the Power Station outage requirements;

It is the responsibility of the FAC Custodian to ensure that inspection Scope of Work and Inspection documents are submitted to RT&D for upload onto Hyperwave.

The FAC Custodian shall ensure that all inspection sheets and images are appropriately archived at the site documentation centre or equivalent electronic backup system within a month after submission to ensure traceability and future retrieval for audit purposes;

All metallurgical evaluation reports shall be appropriately approved/signed off and archived on Hyperwave.

The Technology function will provide periodic feedback to Gx Senior Management with respect to the inspection status per unit at each site using the FAC Outage & FAC SOW/Inspection Tracking Tool [4].

4. AUTHORISATION

This document has been seen and accepted by:

Name Designation

All members as at November 2015

Materials, NDT & Welding Study Committee

All members as at November 2015

Materials Care Group

Joe Roy-Aikins Discipline Manager – Turbine CoE

Chairman – Turbine Study Committee

Noel Lecordier Senior Consultant Engineering (PEIC Turbine)

Member – Turbine Study Committee

Stephanie Marais PEIC Corporate Chemistry Specialist

Member – Water Sciences and Technology Study Committee

Sumayyah Sulliman PEIC Senior Engineer

Member – Water Sciences and Technology Study Committee

Members as at Feb 2016 GX Engineering Mangers Forum






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5. REVISIONS

Date Rev. Compiler Remarks

February 2013 0.1 K Northcott Draft Document for review created from GPL 36-951

March 2013 0.2 L Joubert Realignment of responsibilities and task lists with document structure

March 2013 0.3 SD Marais Provision of Chemistry requirements

December 2013 1 K Northcott Final Document Authorised for Publication

January 2016 1.1 K Northcott First Updated Draft for Internal Review

January 2016 1.2 K Northcott Final Draft for Comments Review Process

February 2016 1.3 K Northcott Final Draft after Comments Review Process

February 2016 2 K Northcott Final Rev 2 Document for Authorisation and Publication

6. DEVELOPMENT TEAM

The following people were involved in the development of this document:

SD Marais (Power Plant Chemistry)

AF du Preez (Corporate Consultant)

7. ACKNOWLEDGEMENTS

None

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