Field Modifications


 Modifications to nuclear plant components are often required as components age. These modifications may be required to improve access for inspection or maintenance, to repair in-service degradation and damage, or to address other plant-related needs. The Babcock & Wilcox Company’s (B&W) experience designing and providing field services to nuclear pressure vessel equipment enables our engineers to design and qualify practical vessel modifications that are optimized for field installation.


B&W’s experience and capabilities include qualification of a large range of field modifications, including:

  • Modification of openings
  • Field-installed inspection ports and handholes (often without the need for welding to the pressure boundary), including unreinforced or partially reinforced designs
  • Installation of Helicoils™ to repair damaged threads
  • Installation of Hydra-Nuts™
  • Operation with damaged or missing studs on openings
  • Changes of gasket materials

Capability and Tools

B&W has developed extensive knowledge in bolt design and analysis, gasket selection, gasket seating design, gasket analysis and seal-weld analysis through years of experience with gasketed and seal-welded openings subject to pressures in excess of 3000 psi.
B&W performs gasket analyses using a variety of methods, both rule-based (ASME and PVRC methods) and numerical-based, using commercial Finite Element (FE) codes (ANSYS®, ABAQUSTM).
Capabilities include:

  • Selection of gaskets based on joint behaviour, gasket stiffness and leakage requirements
  • ASME Code design of gasketed joints/bolts, including thermal transient and fatigue analysis
  • Selection of bolt assembly preloads for good gasket seating and no-leakage during operation
  • Gasket and bolt design using the PVRC method, including interpretation of Room Temperature Tightness (ROTT), gasket test data and their application to bolt design
  • Finite element modeling of non-linear gasket behavior including elastic-plastic modeling for the prevention of gasket leakage
  • Prediction of joint rotation and optimization of joint geometry
  • Fatigue analysis of seal welds 

ANSYS® is a registered trademark of ANSYS, Inc.
ABAQUSTM is a registered trademark of Dassault Systems.
HelicoilsTM is a registered trademark of Emert Technologies.
Hydra-NutsTM is a registered trademark of Curtis-Wright Corporation.