November 2009

DURLON^®
TECHNICAL INFORMATION

Torque loss is inherent in any bolted joint. The combined effects of bolt relaxation, (approximately 10% during the first 24 hours after installation), gasket creep, vibration in the system, thermal expansion and elastic interaction during bolt tightening contribute to torque loss. When torque loss reaches an extreme, the internal pressure exceeds the compressive force holding the gasket in place and a leak or blow-out occurs.

A key to reducing these effects is proper gasket installation. By bringing the flanges together slowly and parallel when installing a gasket and taking a minimum of four bolt tightening passes, following the correct bolt tightening sequence, there is a payoff in reduced maintenance costs and increased safety. Proper gasket installation technique is covered in the our Durlon Technical Handbook.

Proper gasket thickness is also important. The thicker the gasket, the higher the gasket creep which in turn can result in torque loss. On standard ANSI raised face flanges a 1/16" thick gasket is normally recommended. Thinner gasket materials can take a higher gasket load and therefore higher internal pressures.

Even when the installation is ideal, where the bolt stress is uniformly applied to each bolt, and the gasket is properly compressed, problems can still arise. Inherently with time, loosening will occur due to the factors already mentioned. If other factors such as cycling, thermal upsets, water hammer or just a piping system with inadequate pipe supports are present, periodic retorquing might be necessary.

For problem areas, high temperature applications or where there is temperature cycling, or where a flange cannot be retorqued, conical spring washers have been found to be very helpful as an aid to torque retention. They act as a spring and help lessen the effects of torque loss.

Other factors affecting torque loss include:

Finally, having the torque information for the gasket material is helpful as well. Please refer to the torque data that follows.

GASKET INSTALLATION

The importance of proper gasket installation cannot be stressed enough. The following is a basic explanation of how to properly bring the flanges together parallel and in stages, once the gasket is in place to properly compress the gasket. As a minimum, four passes are required. Using the right torque value for the lubricant being used to get the proper gasket compression is important as well.

In the torque tables that follow for Durlon^® non-asbestos gasket materials, it is assumed the flanges are in good condition, anti-seize has not been used on any gasket contact surfaces and a proper installation technique such as what is outlined below is used. Never use any sheet gasket material as insulating washers in flange insulation kits.

NOTE: As a general rule, soft gaskets are intended for service in Class 300 and below. For applications above Class 300 consult your representative.

HOW TO PROPERLY INSTALL A GASKET
(download installation PDF)

• Visually examine and clean flanges, bolts, nuts and washers. Replace components if necessary.
• LUBRICATE the bolts, nuts and nut bearing surfaces.
• Install the new gasket, bolts and nuts. Be sure gasket is properly centered.  DO NOT REUSE old gasket, or use MULTIPLE gaskets.
• Number bolts in cross-pattern sequence according to the appropriate sketch below.
• IMPORTANT! HAND TIGHTEN; then SNUG BOLTS UP to 10/20 FT-LBS torque, but DO NOT EXCEED 20% of Target Torque.
• Check gap for uniformity.
• Starting at the #1 bolt, Use the appropriate cross-pattern tightening sequence in the sketch below for Rounds 1, 2, and 3 and/or Round 4 (each sequence constitutes a "Round").

CLASS 150 ANSI B16.21-78
DURLON^® Gasket Material
Torque: ft-lbs

CLASS 300 RF
ANSI B16.21-78 -  RING GASKETS
DURLON^® Gasket Material
Torque: ft-lbs

SHELF LIFE, STORAGE & HANDLING

• Gasket material should be stored in a cool, dry location.  Avoid storage of material in direct sunlight or near heaters.  Avoid contact with water, oil or chemicals. Gaskets should not be stored so that they become too tightly packed and damaged.
• Aging is a factor that should be considered.  Each material, however, ages differently.  Under normal storage conditions, three/four years is acceptable for compressed materials.  Filled PTFE and flexible graphite can be stored indefinitely.  All full-sized sheets and rolls of Durlon^® compressed materials are date coded and traceable.
• All dust producing processes such as drilling, grinding and sawing should not be used on gasket materials.
• Follow any special instructions for the equipment or fluid to be sealed: for example, oxygen service or low chloride requirements.
• Avoid hanging gaskets on pegs or nails as this may cause distortion of the gasket.  When stocking the shelves or bins where gasket materials are stored, the material should be rotated by placing the older material first or on top with the newer material behind or under it.
• All gasket material should be identified (branded) to guard against misapplication.  Gaskets should be properly marked to insure there is no confusion between different classes and/or sizes.

Warning: Durlon gasket materials should never be recommended when both the temperature and the pressure are at the maximums listed.  Properties and applications shown are typical.  No application should be undertaken by anyone without independent study and evaluation for suitability. Never use more than one gasket in one flange joint, and never reuse a gasket.  Improper use or gasket selection could cause property damage and/or serious personal injury.  The data reported is a compilation of field testing, field service reports and/or in-house testing.  While the utmost care has gone into publishing the information contained herein, we assume no responsibility for errors.  The information and specifications  contained in this website are subject to change without notice. This revision cancels and obsoletes all previous editions.

 
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