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Performance Characterization of Bolt Torquing Techniques: Sealing Technology and Plant Leakage Reduction SeriesProduct ID:1003150
Date Published:26-Mar-2002
File size:7.90 MB
Sector Name:Nuclear
Document Type:Technical Report
FileType:Adobe PDF (.pdf)
Abstract
While controlled torquing is the de facto method of choice for assembly of bolted joints in nuclear plant applications, this preference often stems as much from prevailing wisdom as from objective comparison of the options. Furthermore, many individual details concerning joint assembly remain subjects of debate. As part of its ongoing research on flanged joint leakage prevention, EPRI has reviewed existing guidance on joint assembly practices and conducted a series of controlled tests to generate comparative data. This report presents analytical test results on the four general approaches to bolt torquing, as well as comparative analysis of a number of specific practices and techniques.
BackgroundDebate on the best method for manually tightening a bolted connection has gone unresolved for years. Every vendor, subject matter expert, and end-user seems to have an opinion as to which method will yield the "best" result, even though the desired result often goes undefined. This lack of definition has, in fact, enabled the debate to continue. EPRI research on assembly of bolted connections has demonstrated that a good method is one that enables the technician to repeatedly achieve the intended gasket deflection, which should result in the gasket seating stress needed to effect and maintain a seal over the intended service life of the connection.
Field experience points to controlled torque as the preferred method for achieving the desired gasket deflection, at least in cases where avoidance of leakage is critical. However, no formal technical basis exists to substantiate this preference. The research documented in this report is intended to fill this gap.
Objectiveo To conduct a review of the pertinent guidance from vendors and subject matter experts
o To provide an objective comparison of the performance of the four principal bolted joint assembly techniques
o To perform a comparative analysis of various common procedurally defined practices and "favorite techniques" used by mechanics in the field for tightening bolted connections
ApproachInitial efforts included a review of plant procedures for assembly of bolted flange connections, as well as scrutiny of guidance from several major gasket vendors. Utility input on various techniques of interest was compiled during project discussions at meetings of the EPRI Fluid Sealing Technology Working Group. This input led to the development of a general test plan for characterizing performance of different assembly techniques and practices. In accordance with this plan, a series of experimental tests was performed using EPRI's patented Bolted Joint Performance Demonstration Unit. Researchers first established a performance baseline for gaskets to be used in the experiments. They then ran the tests outlined in the plan, collecting data on individual bolt forces and gasket deflection for each assembly step of the techniques and practices in question. The data was recorded in Microsoft Excel. Calculations, showing percent total gasket deflection, average bolt force, and range of bolt force across the connection, were performed automatically. In addition, charts were prepared, illustrating bolt force in the joint at the conclusion of each assembly step.
ResultsThe research confirmed the importance of several factors previously identified by EPRI as being key to effective bolted joint assembly. The research also led to the identification of three additional factors with significant potential for contributing to improved assembly of bolted joints. Experiments quantified the value of these factors, in combination with the previously identified key factors, in terms of high repeatability rates and low scatter rates.
EPRI PerspectiveBecause gasketed joints represent virtually all of the critical piping system joints found in nuclear power primary system applications, objective data on the best practices for their assembly is of widespread interest. EPRI believes that this report is of significant potential value to members concerned with improving plant safety, operability, and availability, while reducing associated operations and maintenance costs.
Program
2002 Program 41.05.01 Nuclear Maintenance Applications Center
Keywords
- Bolted Joints
- Comparative Evaluation
- Leakage
- Performance Testing
- Reactor Piping
- Seals
Report
000000000001003150
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