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Tube Plugging

Tube Plugging

Rapid Plugging System

The primary scope of inspection and repair in today’s steam generators (SG) is tube eddy current inspection and plugging. BWXT took a fresh look at these processes, with a focus on automation, speed and performance. The result? Systems and hardware that provide high production rates and superior quality. Our plugging installation process takes advantage of newly developed robotics to integrate well with the inspection process and to minimize equipment needs. Mechanical plugs have historically been leak limiting devices, whereas our new plug offers leak-tight performance, facilitated by the application of a nickel band. Other features include minimal protrusion beyond the tube end and ease of Eddy Current Technology (ET) and visual inspection.

A major advantage of BWXT’s plugging system is its one-step process design; plugs are inserted and rolled in a single step. At the core of BWXT’s Rapid Plugging System is the innovative design of our hollow spindle plugging tool. This universal tool is designed to deliver and control all aspects of the mechanical plugging installation and removal process. The plug and plug expander, or in the case of removal the plug shrinker and puller, are delivered remotely through the hollow spindle tool. This unique design reduces tooling costs, equipment quantities, cycle time, platform setup, dose and overall schedule.The plugging tool is designed with an electric motor as the power source, providing several improvements over industry standard pneumatic motors. Computer control of the electric motor provides consistent performance, and provides the ability to control, monitor, and record torque, variable speed and rotational position – capabilities not available in current tools. Fiveroller plug expanders provide more contact area than conventional three-roller expanders, thereby reducing work hardening and spring-back effect of the tube.

Another major advance is BWXT’s Rapid Plug Loader, inspired by the successful deployment of our rapid welded plugging system. Equipped with dual magazines holding 25 plugs each, the plug loader is well suited for both small-scale and larger plugging campaigns. Plugs are fed into the loader from the magazine, a pusher unit inserts the plug expander into the plug, and the unit delivers the plug/ expander assembly through flexible conduit to the tool head and into the target tube. Machine Vision provides verification of proper location, and the roll process is computer controlled and verified for acceptance. As the robot moves to the next plugging location, the process sequence is repeated. The high degree of automation and efficiency afforded by the system provides a cycle time of less than 5 minutes, achieving exceptional production rates.


BWXT has designed, qualified and manufactured tube stabilizers for more than 25 years. We have stabilizers designed and qualified for a variety of applications, including full length Once-Through Steam Generators (OTSG), U-bend, top-of-tubesheet and tube support plate stabilizers. Additionally, our field teams have been responsible for the installation of more than 5,000 flexible stabilizers.

Speed of installation was a major factor both in the design of our stabilizers and the development of our tooling. Our stabilizers attach to our mechanical rolled plug, and are designed for rapid installation similar to our plugging process. Stabilizers are delivered through standard ET conduit via a flexible pusher cable, incorporating a pneumatic bladder that grips the plug ID. Location is verified by Machine Vision, and the plug/stabilizer assembly is subsequently rolled using our universal plugging tool. Tight integration with our inspection system results in a design and process that provides cycle times of less than 5 minutes; legacy issues with manipulators and tooling that cannot accommodate the friction and reaction forces associated with stabilizer insertion are eliminated. And, our stabilization system utilizes the same control system and internal electric motor as the rolled plugging system, requiring reduced tooling and controls and providing an easy, seamless transition between stabilization and plugging.

Key Features and Benefits:

  • PC-based controls and software; smooth transition from inspection to repair
  • Field proven systems based upon existing rapid repair tooling
  • Universal, modular multi -purpose tooling reduces equipment needs, system complexity and cost
  • Tooling is powered by industrial electric motor assemblies which provide superior feedback and control of torque, rotational position and RPM
  • High degree of automation minimizes human performance variances and provides state-of-the industry repair production rates 

Welded Tube Plugging

BWXT's rapid welded plugging system is one of the most advanced weldedRapid Steam Generator Tube Plugging
plugging systems in the industry. Our system was developed to maximize productivity and weld quality, and has been used to install thousands of welded plugs rapidly and efficiently. System advancements include unique cleaning tooling, rapid plug delivery, and multi -tube capabilities for densely plugged areas or large-scale repair campaigns.

BWXT leads the industry in productivity, quality and innovation for welded plug installation with ourqualified plug design and specifically engineered installation tooling. BWXT's welded plugs are designed to remain in place during all operating conditions for the life of the steam generator (SG). The
plugs are installed in the tubesheet following tube sample removal, and are a viable, cost effective alternative to traditional mechanical rolled plugs. A pressure boundary is formed when the plugs are welded to the tube and/or tubesheet, thereby providing a structural integrity pressure boundary and eliminating leakage between the primary and secondary sides. The plugs are safety-related and are qualified in accordance with ASME Boiler an Pressure Vessel Code, Section XI.

Our welded plug design includes the following features:

  • Can be installed into 100% of the SG tubes
  • Can be installed in flush or stub tube ends
  • Plug can be removed by machining
  • Plug material is thermally treated alloy 690

Our welded plugging system has been developed to maximize productivity by reducing the time for each process step. Welded plug installation requires up to six steps per tube end – brushing, size rolling, swabbing, plug insertion, welding and inspection. Focusing on robot speed, tooling performance, and multi -tube processes, BWXT has developed one of the fastest welded SG plugging systems. Our rapid plug delivery system has two major components: a rapid plug injector and a plug inserter. The rapid plug injector is designed to deliver plugs to the tubesheet as fast as the Zetec ZR-100 robot can reposition from one tube to the next. A pneumatic cylinder shuttles under a gravity feed to dispense up to 25 plugs per magazine.The plug inserter, which is attached to the end of the robot, drives the plug into the tube or tubesheet hole. The plug inserter is fitted with a plug gating device that directs the plug from the injector to the inserter. Within seconds a new plug is in position to be inserted into a subsequent tube.

The welded plugging process is also enhanced with automated end effecter change out and consumable storage. This tooling can be used in larger campaigns, or when access to the SG platform is limited, allowing productivity to continue without platform support.

BWXT uses computer-controlled welding power supplies and software for recording welding parameters in real time. Coupled with a unique visual inspection camera, we perform a validation of our installed weld

Key Features and Benefits:

  • BWXT’s welded plug design meets or exceeds all requirements for a Class 1 Safety-Related component
  • Field proven design is one of the industry’s fastest remote welded plugging systems
  • Production cycle time of 12 minutes per plug is achievable for large volume repair campaigns
  • Data collected during the welding process can be displayed for time, amps, volts and travel
  • Tooling is delivered via a single robotic platform
  • PC-based controls and software