Page 43 - Design Criteria.qxd

44 ® Welcome to the Next Generation of Sealing Technology
SECTION III
Gasket Installation
A FLEXITALLIC gasket will provide a reliable seal when properly installed in the application for which it was designed. Please
remember that the performance of a bolted joint is not solely dependent on the gasket itself, but on a combination of variables, many
of which are outside the control of the gasket manufacturer. Experience has shown that leakage is not necessarily a sole indication of
a faulty gasket, but is more likely to be the result of improper installation, assembly or bolting practices, damaged flanges, or a com-
bination of the myriad of variables associated in a bolted gasketed assembly. When installing the gasket the following are to be con-
sidered:
Gasket Quality
Obviously gasket quality is important. Always deal with reputable suppliers and/or manufacturers who are capable of high quality
products and sound technical support.
NEVER INSTALL A PREVIOUSLY USED GASKET!
Flange Surfaces
The condition of flange surfaces, as well as the proper flange material selection play an important part in achieving a leak-free joint
assembly. Assure that the following are within acceptable limits:
• Surface finish • Waviness
• Flatness • Surface imperfections
• Parallelism
For optimum gasket performance Flexitallic recommends that the flange surface finishes listed in the table on page 45 be used for the
respective gasket selected. To assure proper and even compression of the gasket we recommend that parallelism be within 0.2 mm
(0.008”), flatness and waviness are kept at better than 0.2 mm (0.008”). We suggest that the allowable imperfections do not exceed
the depth of the surface finish grooves, and that any radial marks are no deeper than the depth of the flange surface finish and less than
50% in length of the overall gasket sealing surface width.
Fasteners
It is important that the proper studs/bolts and nuts are selected to assure joint integrity. Improper selection of these may compromise
the entire joint assembly. The following list is to be considered when selecting fasteners:
• Type • Proper material
• Grade • Appropriate coating or plating
• Class • Correct stud/bolt length
See the table on page 52 for temperature rating of stud/bolt grades.
Assembly
In an effort to achieve a high degree of success in attaining a leak-free joint several steps are required. It is imperative that a regi-
mented bolt up procedure is applied. As a minimum the following is suggested:
• Install a new gasket on the gasket seating surface and bring the mating flange in contact with the gasket.
• Do not apply any compounds on the gasket or gasket seating surfaces.
• Install all bolts, making sure that they are free of any foreign matter, and well lubricated. Lubricate nut bearing surfaces as well.
(Lubrication will not be required for PTFE coated fasteners.)
• Run-up all nuts finger tight.
• Develop the required bolt stress or torque incrementally in a minimum of four steps in a crisscross pattern. The initial pre-stress
should be no more than 30% of the final required bolt stress. After following this sequence, a final tightening should be performed
bolt-to-bolt to ensure that all bolts have been evenly stressed.
Note: The use of hardened washers will enhance the joint assembly by reducing the friction due to possible galling of the nut bearing
surfaces.