Performing maintenance tasks correctly the first time has become increasingly important to end users. Today’s end users are tasked with doing more work with less time, fewer resources and smaller staffs while responding to the increase in environmental and other equipment-related pressures. The ability to correct a mistake, such as a flange leak resulting from improper gasket selection or installation, is a luxury of the past. Gasket selection and installation are two concerns that can be improved if the gasket material manufacturers are consulted from the beginning. However, using a gasket manufacturer’s published torque data has pros and cons.
Many associations, societies and regulatory agencies have rewritten and redeveloped emissions and leakage standards and controls year after year. When the process rules are changed, manufacturers of seals, packing and gaskets are forced to implement changes as well. The manufacturers either produce seals that are better suited to handle the new regulations or they drop out of the market. These changes affect the way end users must look at the quality of flexible graphite and its ability to seal. Click here to read more.
The purpose of surface finish is to allow a gasket to conform to and seal the flange face. Ensuring that the choice of gasket and surface finish work together to maintain the appropriate level of sealing stress on the gasket is important. Click here to read an article that identifies some of the typical damage that occurs to a flange face, what the effect is, and discusses a way to identify the practical limits for them.
Gasket blowout is the most catastrophic of gasket failures. It usually occurs with no discernable warning and
causes a sudden and significant release of internal pressure, usually accompanied with loud popping sound or whistle. Depending on the process being contained and/or the amount of stored energy at the time, the result can be fatal.
Part One of a two-part Sealing Sense series brings attention to the balance of forces present at the potential
moment of gasket blowout and provides guidance on how to protect against this type of gasket failure. Equations are provided to assist with evaluating these forces and results are presented to show that to protect against blowout, clamping force can be significantly more important than gasket tensile strength.
Part Two discusses the two most important strategies to use for applying the correct clamping force. End users control these strategies. One involves developing a bolt load solution that optimizes
the inherent strength of the BFC components. The other is following an installation procedure that ensures that the specified bolt load is reached and evenly distributed around the face of the gasket.
Click here to read Part One and Part Two of this series.
The purpose of using a torque wrench is to apply the target load for a specific amount of stress on a gasket. For any given combination of gasket, bolt and flange, a stress range will ensure that the gasket will seal while, at the same time, protecting from over tightening that may cause damage to one of these components. Failure to remain within this stress range may result in environmental concerns, safety issues and downtime that can be expensive and dangerous. Understanding the types of torque wrenches, their advantages and how to maintain them will help operators apply the correct stress to gaskets. Specific guidance on a torque wrench’s use can be found in ASME PCC-1-2013.
Over the years, the FSA Gasket Division has provided insights into many specific sealing and gasket issues. Even with the educational effort on the gasket itself, chances are that end-users of gaskets will be confronted at some point with a bolted flange connection that leaks. When this happens, those involved will usually still consider the gasket as the probable cause of the leakage. So it continues important to share the knowledge and experience of the gasket material manufacturers to help users understand how other factors related to the gasket, but not the gasket itself, may contribute to the sealing difficulties they face. The experience of most gasket material manufacturers suggests that a very high percentage of bolted flange connections that leak (perhaps 75 to 85 percent) do so as a result of bolted flange connection issues other than the gasket itself. These factors usually relate to installation and assembly problems and limitations. A bolted flange connection is a complex combination of many factors. All these various elements are interrelated so depend upon one another to achieve a successful seal.
The critical nature of installation and assembly has been recognized for many years but only relatively recently have best practices been compiled. This was accomplished with publication of the ASME PCC-1-2000 “Guidelines for Pressure Boundary Bolted Flange Joint Assembly.” An update to this document, PCC-1-2013, recently has been published with focus on developing standard qualifications and requirements for the training and certification of flange assemblers.
Some of the most frequent issues dealing with the installation of a gasket and the assembly of a flange include:
Under loading of the Gasket
Uneven Compression of the Gasket
Application of a used gasket
Poor torque/load control of fastener installations
Lack of standard proper installation procedures for outside contractors
The gasket is but one of many reasons a bolted flange joint can leak. Even when all the complex inter-related components work in perfect harmony, the single most important factor leading to success or failure will be attention given to proper installation and assembly procedures by the craftsman installing the gasket. If done properly, the assembly will remain leak-free for the target life expectancy.