November 2009

DURLON®
TECHNICAL INFORMATION

TORQUE LOSS

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:

Rate of heat up.
New vs. used bolts or studs
Use of hardened steel washers
Lubrication of bolts, nuts and nut facings
Method of bolt up. Order of efficiency from least to greatest:
      1. Wrench and cheater bar or sledge hammer
      2. Air impact gun
      3. Torque wrench
      4. Hydraulic torque wrench
      5. Hydraulic stud tensioners

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").

  • Final Torque: _________ ft-lbs

4-bolt and 8-bolt flanges:

  • LUBRICATE, HAND TIGHTEN, then
    SNUG up bolts

  • Round 1 - Tighten to 25% of- final torque

  • Round 2 - Tighten to 50% of final torque

  • Round 3 - Tighten to 100% of final torque

12-bolt flanges and above:

  • LUBRICATE, HAND TIGHTEN, then
    SNUG up bolts

  • Round 1 - Tighten to 20% of final torque

  • Round 2 - Tighten to 40% of final torque

  • Round 3 - Tighten to 80% of final torque

  • Round 4 - Tighten to 100% of final torque

Check gap around the circumference between each of these rounds, measured at every other bolt. If the gap is not reasonably uniform around the circumference, make the appropriate adjustments by selective bolt tightening before proceeding.

  • Rotational Round - 100% of Final Torque (same as Round 3 or 4 above). Use ROTATIONAL, clockwise tightening sequence, starting with Bolt No. 1, for one complete round and continue until no further nut rotation occurs at 100% of the Final Torque value for any nut.

  • Final Round - RETORQUE. After twenty-four hours repeat Round 3 or 4 (above) followed by a Rotational Round. Tests show that a large percentage of the short-term bolt preload loss occurs within twenty-four hours after initial tightening. This Round recovers this loss. This is especially IMPORTANT for PTFE gaskets.

TIGHTENING METHODS:

  • Hand Wrench
  • Manual Torque Wrench
  • Hydraulic Torque Wrench
  • Impact Wrench

  • Other

  

 
* For tightening pattern for large diameter flanges, contact technical services at (713) 467-1316, or tech@durlon.com

Torque Values – ASME B16.5 Flanges

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

Flange Raised Face/Ring Gaskets Flat Face/Full Face Gaskets * Bolt Tighten Seq
Size 1st 2nd Final 1st 2nd Final Dwg*/No. Size
1/2" 4 8 16  15 35 70 4-bolt 1/2"
3/4" 6 12 23  15 35 70 4-bolt 1/2"
1" 8 15 30  15 35 70 4-bolt 1/2"
1-1/4" 12 24 45  15 35 75 4-bolt 1/2"
1-1/2" 14 28 56  15 35 75 4-bolt 1/2"
2" 25 50 113 35 75 150 4-bolt 5/8"
2-1/2" 25 50 113 35 75 150 4-bolt 5/8"
3" 33 66 130 35 75 150 4-bolt 5/8"
3-1/2" 36 92 140 35 75 150 8-bolt 5/8"
4" 25 50 113 35 75 150 8-bolt 5/8"
6" 25 50 113 65 130 270 8-bolt 3/4"
8" 50 100 202 65 130 270 8-bolt 3/4"
10" 80 160 327  110 220 436 12-bolt 7/8"
12" 80 160 327  110 220 436 12-bolt 7/8"
14" 120 240 492  160 320 655 12-bolt 1"
16" 120 240 492  160 320 655 16-bolt 1"
18" 180 365 731  240 480 975 16-bolt 1-1/8"
20" 180 365 731  240 480 975 20-bolt 1-1/8"
24" 260 520 1036  345 680 1380 20-bolt 1-1/4"
Note: It is assumed that new ASTM A193 Gr. B7 studs with 2H heavy hex nuts and hardened steel washers are used and studs, nuts and nut facings are lubricated with a never-seize paste using the installation and bolt tightening practices outlined above. Torque is based the higher of 40% of bolt yield, T3 or 4800 psi gasket stress up to either the maximum allowable material stress or a maximum bolt yield of 60%. The above was calculated using the proposed ASME Gasket Constants (ROTT Testing, Ecole Polytechnique) for each material.
 
* Flat face flanges using full face gaskets, the recommended torque value is generally the maximum allowable torque based on the allowable bolt area.  Flat face flanges have the same bolting as raised face flanges but roughly 3 to 4 times more surface / contact area.  This makes flat face flanges very difficult to seal unless using a gasket with low compression characteristics such a a rubber gasket. 

The user should be aware that there most likely is insufficient bolt area to adequately seal flat face flanges.
 
NOTE:  Bolt stresses may exceed ASME allowables.


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

  ANSI B16.5 Class 300 RF
Flange Torque / Round (ft-lbs) Bolt Tighten Seq*
Size 1st 2nd Final Dwg/No. Size
1/2" 4 8 16 4-bolt 1/2"
3/4" 10 20 40 4-bolt 5/8"
1" 10 20 40 4-bolt 5/8"
1-1/4" 14 28 55 4-bolt 5/8"
1-1/2" 23 46 90 4-bolt 3/4"
2" 15 30 60 8-bolt 5/8"
2-1/2" 23 46 90 8-bolt 3/4"
3" 31 62 125 8-bolt 3/4"
3-1/2" 35 70 140 8-bolt 3/4"
4" 45 90 180 8-bolt 3/4"
6" 45 90 190 12-bolt 3/4"
8" 75 150 297 12-bolt 7/8"
10" 78 156 310 16-bolt 1"
12" 115 230 460 16-bolt 1-1/8"
14" 100 200 400 20-bolt 1-1/8"
16" 143 286 570 20-bolt 1-1/4"
18" 161 322 645 24-bolt 1-1/4"
20" 178 356 710 24-bolt 1-1/4"
24" 275 550 1100 24-bolt 1-1/2"

Note: It is assumed that new ASTM A193 Gr. B7 studs with 2H heavy hex nuts and hardened steel washers are used and studs, nuts and nut facings are lubricated with a never-seize paste using the installation and bolt tightening practices outlined above. Torque is based the higher of 40% of bolt yield, T3 or 4800 psi gasket stress up to either the maximum allowable material stress or a maximum bolt yield of 60%. The above was calculated using the proposed ASME Gasket Constants (ROTT Testing, Ecole Polytechnique) for each material.
 
NOTE:  Bolt stresses may exceed ASME allowables.

SHELF LIFE, STORAGE & HANDLING

The shelf life for Durlon® gasketing products is as follows:

          Durlon® compressed sheet materials stored under normal conditions, the shelf life is three to four years.

          Durlon® PTFE sheet - unlimited

          Durlon® flexible graphite and CFG - unlimited
  • 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.