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ACL® Clamp Life
Introduction
All common sanitary clamp unions utilise similar parts. The majority of the component parts do not experience the usual types of degradation that other engineered systems experience. The majority of the degradation is experienced by the threaded fasteners and their contact points.
The removal and thus retightening of threaded fasteners results in a detrimental effect on the achievable bolt pre-load. As the bolt pre-load is the determining factor in the sealing integrity of the sanitary union, it should be considered as the critical component in the assembly. The bolt pre-load is the force that clamps the union together and prevents gasket blow out and movement of the constituent parts.
In the sanitary union, there exists a balance between the gasket sealing, maintaining the gasket intrusion limit, avoiding galling and clamp longevity. Elastomeric gaskets are the most commonly used gasket in the sanitary union; they are also the most susceptible to degradation due to their molecular structure. As a result of this, it is a requirement that they are frequently changed. This means that the clamp has to be removed and re-assembled.
It is a well known fact that the achievable clamping force (pre-load) for a threaded component is reduced after the first tensioning (utilising the same torque value).
Typical Areas of Stress Relaxation in a Sanitary Clamp
Calculation of Bolt Preload of ACL® Clamps*
T = K*F*D
where,
K = estimated nut friction factor
T = bolt torque
D = nominal bolt diameter
Then,
F = T / (K*D)
* Source: ACL® Clamp Nut Torque Guide)
Coefficients of Friction for ACL® Fasteners
| Stainless on stainless: | 0.3 |
| General sanitary lubricant: | 0.2 |
Table 1. ACL® Clamp Bolt Preload Values for Elastomeric Seals (Dry Assembly – No Lubrication)
| SH | SS | ASME VIII | S-TYPE | ||||||
|---|---|---|---|---|---|---|---|---|---|
| NOMINAL SIZE (INCHES) | FLANGE SIZE | TORQUE (NM) | BOLT PRELOAD (N) | TORQUE (NM) | BOLT PRELOAD (N) | TORQUE (NM) | NOLT PRELOAD (N) | TORQUE (NM) | NOLT PRELOAD (N) |
| 0.5 | 25 | 2 | 849 | 2 | 818 | 2 | 849 | ||
| DN10 | 34 | 2 | 849 | 2 | 818 | 2 | 849 | ||
| 1.5 | 50.5 | 2 | 849 | 2 | 625 | 2 | 515 | 2 | 849 |
| 2 | 64 | 2 | 849 | 2 | 625 | 2 | 515 | 2 | 849 |
| 2.5 | 77.5 | 2 | 849 | 2 | 625 | 2 | 849 | ||
| 3 | 91 | 3 | 1274 | 3 | 981 | 3 | 772 | 3 | 1274 |
| 3.5 | 106 | 3 | 1274 | 3 | 981 | 3 | 1274 | ||
| 4 | 119 | 3 | 1274 | 3 | 981 | 3 | 772 | 3 | 1274 |
| 4.5 | 130 | 3 | 1699 | 3 | 1308 | 4 | 1699 | ||
| 5 | 144.4 | 4 | 1699 | 4 | 1090 | 4 | 1030 | ||
| 5.5 | 155 | 4 | 1308 | 4 | 1090 | ||||
| 6 | 167 | 5 | 1635 | 4 | 1090 | 4 | 1030 | 4 | 1699 |
| 6.625 | 183 | 5 | 1635 | 5 | 1363 | 5 | 1287 | ||
| 8 | 217.4 | 5 | 1635 | 6 | 1635 | 6 | 1545 | ||
| 8.625 | 233.5 | 6 | 1962 | 6 | 1635 | 6 | 1545 | ||
| 10 | 268 | 8 | 2616 | 8 | 2060 | ||||
| 10.625 | 286.1 | 8 | 2616 | ||||||
| 12 | 319 | 10 | 3270 | 10 | 2575 | ||||
| 12.625 | 338 | 10 | 3270 |
Table 2. ACL® Clamp Bolt Preload Values for Polymeric Seals (Lubricated Assembly – FDA Lubricant)
| SH | SS | ASME VIII | S-TYPE | ||||||
|---|---|---|---|---|---|---|---|---|---|
| NOMINAL SIZE (INCHES) | FLANGE SIZE | TORQUE (NM) | BOLT PRELOAD (N) | TORQUE (NM) | BOLT PRELOAD (N) | TORQUE (NM) | NOLT PRELOAD (N) | TORQUE (NM) | NOLT PRELOAD (N) |
| 0.5 | 25 | 6 | 3822 | 6 | 818 | 6 | 3822 | ||
| DN10 | 34 | 6 | 3822 | 6 | 818 | 6 | 3822 | ||
| 1.5 | 50.5 | 6 | 3822 | 6 | 625 | 10 | 3862 | 6 | 3822 |
| 2 | 64 | 6 | 3822 | 6 | 625 | 10 | 3862 | 6 | 3822 |
| 2.5 | 77.5 | 6 | 3822 | 6 | 625 | 6 | 3822 | ||
| 3 | 91 | 9 | 5733 | 9 | 981 | 15 | 5793 | 9 | 5733 |
| 3.5 | 106 | 9 | 5733 | 9 | 981 | 9 | 5733 | ||
| 4 | 119 | 9 | 5733 | 9 | 981 | 15 | 5793 | 9 | 5733 |
| 4.5 | 130 | 10 | 6370 | 12 | 1308 | 10 | 6370 | ||
| 5 | 144.4 | 10 | 6370 | 20 | 1090 | 20 | 7724 | ||
| 5.5 | 155 | 16 | 7848 | 20 | 1090 | ||||
| 6 | 167 | 20 | 9810 | 20 | 1090 | 20 | 7724 | 10 | 6370 |
| 6.625 | 183 | 20 | 9810 | 25 | 1363 | 25 | 9656 | ||
| 8 | 217.4 | 20 | 9810 | 30 | 1635 | 24 | 9269 | ||
| 8.625 | 233.5 | 24 | 11772 | 30 | 1635 | 24 | 9269 | ||
| 10 | 268 | 32 | 15696 | 32 | 12359 | ||||
| 10.625 | 286.1 | 32 | 15696 | ||||||
| 12 | 319 | 37.5 | 18394 | 40 | 15449 | ||||
| 12.625 | 338 | 37.5 | 18394 |
Lubrication
As can be seen in the chart below, repeated use of lubricated or unlubricated fasteners will usually result in a reduction of achievable bolt preload. This is an important consideration for the sanitary union as it will affect the intrusion of the gasket and the sealing reliability.
In order to maintain the performance of your hygienic processing system, it is recommended that the clamps are replaced after a maximum of ten assembly cycles. This can of course be extended if the operator is happy with the condition and performance of the clamp.
References
Eccles, W., Sherrington, I. and Arnell, R., 2010. Frictional changes during repeated tightening of zinc plated threaded fasteners. Tribology International, 3(4), pp.700-707.
The Effect of Lubrication on the Repeated Tightening of EZP Fasteners*
* Source: Eccles, Sherrington and Arnell, 2010
All technical information and advice given here is based on our previous experiences and/or test results. We give this information to the best of our nowledge, but assume no legal responsibility. Customers are asked to check the suitability and usability in the specific application, since the performance of the product can only be judged when all necessary operating data are available. Specifications are subject to change without notice. ACL’s terms and conditions of sale apply to the purchase and sale of the product.