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Areas of Activities
Top Products
Products & Services
PLUGGING OF STEAM GENERATOR TUBES
In order to prevent the flow of media through the defective steam generator INETEC applies mechanical plugging technology for installation of leak resistant plugs on both tube ends.
UP TO NOW, INETEC INSTALLED MORE THAN 15000 MECHANICAL PLUGS ON WWER AND PWR NPP’S WITH EXCELLENT RECORD OF NO PLUGS LEAKING OR MOVING FROM 1989.
Applications
With respect to time of plug installation and quality of joint, worldwide experience shows that mechanical plugging technology is the most effective method. It has been successfully applied on different steam generator models such as Westinghouse, Combustion Engineering, Babcock & Wilcox, Candu, VVER SG models and others.
The main characteristics of mechanical plugging technology are the following:
• Fast plug installation;
• Plug removal possibility;
• Small number of simple installation steps;
• Possibility to control plugging process;
• Possibility of in-service inspection of plug;
• Very good records in service life.
Plug Designs
• The plug material is INCONEL 690 because of its superior resistance to corrosion degradation.
• The plugs are manufactured in various dimensions in order to fit various SG tube diameters.
• The plugs are machined and inspected in accordance with strict manufacturing and inspection procedures.
Two basic mechanical plug designs:
1. MECHANICAL RIBBED PLUG
• two assembly device which consists of cylindrically shaped shell and tapered expander enclosed within the shell.
• the outer ribs interact with tube and form leak resistant joint.
• commonly applied on VVER steam generators.
2. MECHANICAL ROLLED PLUG
• cylindrically shaped hollow shell
• plug outside diameter interact with tube internal diameter and form leak resistant joint
• commonly applied on PWR steam generators
Plugging Equipment
Standard manipulators and control systems, applied for eddy current inspection of steam generator tubes is used for performance of plugging activities as well:
* PWR steam generators: SM-25 manipulator
* WWER steam generators: INETEC DPS manipulators
* Software for plugging performance is part of software package for steam generator EC inspection;
* Special plugging equipment tool and control system are mounted and integrated in standard eddy current examination systems.
* Positioning of manipulator is achieved by application of most modern Machine vision feature which provides accurate fixture location in automatic mode.
Plugging Performance
Mechanical plugging performance consists of several simple installation steps depending of plug design:
| ROLLED PLUG: | RIBBED PLUG: |
| Tube cleaning | Tube end rolling |
| Tube end rolling | Tube rolling |
| Plug installation | Plug installation |
Plugging Quality Control
Quality of plugging process may be controlled through the:
• Control of equipment calibrations;
• Control of maintenance activities;
• Control of plugging position;
• Control of installation parameters:
• Rolled plug – recording of rolling torque versus the time;
• Ribbed plug – recording of pressure and expander travel versus the time.
Mechanical Plug Qualification
Plug design verification:
- tube dimension variations
- helium test
- hydrostatic test
- hydrostatic test
- transient test
- corrosion test
- tensometry
- metalography
- stress and strain analysis
Qualification of plugging system:
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plug installation process
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manipulator
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plugging equipment
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field procedures
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personnel
Plug Removal
• The great advantage of mechanical plug application is its possibility of plug removal.
• Deplugged tubes may remain in service without any consequences on its integrity
• INETEC applies two plug removal technologies:
o hydraulic plug removal – for manual removal;
o drilling plug removal – for automated removal.
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