Technical Article
Figure 4 . Figure 5 .
Notably , lower gasket stress significantly impacts relaxation . In the case of ePTFE ( a high-stress relaxation gasket ), when under-tightened the stress loss surged to 2.4 times that of the baseline level . On the other hand , in cases of over-tightening , the stress loss for the baseline and over-tightened states showed relatively minor differences , suggesting that beyond a certain stress threshold , relaxation becomes less pronounced . In all cases , the effect of dwell time followed similar trends , though differing in magnitude .
Of particular note is the significant decrease in load retention from no retorque to the 24 hour dwell time for the under-tightened state . Since industry research has shown that the overwhelming majority of industrial facilities do not follow proper torque and flange assembly best practices , resulting in under-tightened flanges , the value of a retorque , particularly on high-relaxation materials like PTFE , is made even more critical .
The spiral wound gasket ( a low-load relaxation gasket ) also performed as expected ( Figure 5 ), showing a considerably lower impact on load retention when under or over-tightened , resulting in minimal differences in gasket stress concerning the retorque dwell time . As a result , not all of the dwell time intervals were tested for the additional torque levels .
Figure 6 . Figure 7 .
and type , shorter dwell times , as brief as 15 minutes , can yield significant improvements in stress loss without compromising gasket performance . Additionally , in critical services , opting for a longer dwell time to minimize preload loss and maximize tightness could be worth considering , as well as utilizing gaskets that exhibit lower overall stress-relaxation .
This research opens the door to further exploration . Investigating additional materials , such as rubber , and evaluating the impact of gasket installation stress for various gasket types could provide even deeper insights into the impact of dwell time . In their findings , Girão , Meira , and Veiga concluded that optimizing dwell time is not merely about expediting installations and reducing downtime ; it is about enhancing the overall efficiency and reliability of industrial plant operations . Tailoring dwell time to specific gasket materials and styles presents a viable pathway to more effective maintenance operations and improved profitability , sustainability , and efficiency .
About the Author
Zac Hoover is a graduate of Missouri State University and currently holds the position of Technical Support Service Specialist at Teadit North America ( TNA ). With nearly five years of industry experience , he provides on-site technical support for local customers and creates application-specific gasket drawings . Additionally , he oversees the testing procedures conducted in the company ' s research and development lab in Pasadena , TX while also managing the engineering intern program at TNA which contributes to the development of emerging talent within the organization .
Alternative Assembly Patterns : A Time-Saving Triumph
In their investigation , Girao , Meira , and Veiga also compared two ASME PCC-1 installation methods : the Legacy Cross-Pattern Numbering System and the Alternative Assembly Pattern # 3 . The difference in the results for load retention and dwelltime , even in the under and over-tightened states , were negligible ; with the Alternative Pattern # 3 slightly outperforming the Legacy Pattern . However , the former , a more streamlined approach , proved to be approximately 45 % faster in execution . This revelation underscores the potential for substantial time savings in plant maintenance operations during flange bolt-up .
Conclusion
The dwell time dilemma is a critical consideration in bolted flanged joint installations . The study done by Girão , Meira , and Veiga demonstrates that a one-sizefits-all approach to dwell time may not be optimal . Depending on gasket material
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