Design improvement reduces gasket crush
Gaskets are crushed more frequently than many end users realize . Some maintenance professionals claim that is all they see when they separate a leaking flange . Many simply replace the gasket rather than investigating the cause of the failure in depth .
By Justin Zhao , AIGI Environmental Incorporated
Gasket crush is a significant threat to plant reliability . This problem causes leaks , which can lead to a dangerous plant situation , especially if a hazardous fluid is involved . This issue is unpredictable and introduces variability into plant operations . All types of gaskets ( metal , non-metal , and composite ) experience gasket crush . If a gasket design fails on the first installation , plant personnel can replace it with a new design during the next plant shutdown . However , if a gasket has worked nine times without a problem , then leaks on the tenth installation because of gasket crush , an unplanned maintenance response is required . Users have two options for reducing gasket crush : better torquing procedures , which can be difficult , and better gasket design , which is easier to implement .
Torquing procedures
In a crushed gasket , different compression patterns are visible – sometimes on one side of the gasket , sometimes on opposite sides and sometimes all over the gasket . These patterns point to over-compression . The most obvious conclusion is that something was wrong with the torque is based on a few important assumptions . It must be noted that sophisticated torque equipment , such as torque wrenches or bolt tensioners , is often used during installation accuracy , which is generally between
Figure 1 . Round-edged beveled ribs compress under pressure . Graphics courtesy of AIGI Environmental Inc .
Figure 2 . A stop-step feature prevents the flexible ribs from over-compressing . Graphics courtesy of AIGI Environmental Inc .
5 and 15 percent at best . The aforementioned assumptions include : Bolts must be well-lubricated with a lubricant of known coefficient of friction , because unlubricated bolts can consume up to 50 percent of the torque load . Torque typically is calculated based on the bolt material , not the required load of the gasket material , which is usually too high for the gasket need . Personnel only have access to a
Crushing Pressure , Mpa
250
200
205
150
100
50
0 Fishbone Gasket 22.5mm OD , 4.5mm thick
54
Spiral Wound Gasket 22.5mm OD , 4.5mm thick
Figure 3 . Crush resistance test results with a pressure of 205 MPa ( 29,732 psi ). Graphics courtesy of AIGI Environmental Inc .
22 Valve World April 2023 www . valve-world . net