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)
0.525284928182849
DN1034284928182849
1.550.52849262525152849
2642849262525152849
2.577.5284926252849
391312743981377231274
3.510631274398131274
4119312743981377231274
4.5130316993130841699
5144.4416994109041030
5.51554130841090
616751635410904103041699
6.625183516355136351287
8217.4516356163561545
8.625233.5619626163561545
102688261682060
10.625286.182616
12319103270102575
12.625338103270

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)
0.52563822681863822
DN103463822681863822
1.550.563822662510386263822
26463822662510386263822
2.577.563822662563822
39195733998115579395733
3.510695733998195733
411995733998115579395733
4.5130106370121308106370
5144.4106370201090207724
5.5155167848201090
6167209810201090207724106370
6.625183209810251363259656
8217.4209810301635249269
8.625233.52411772301635249269
1026832156963212359
10.625286.13215696
1231937.5183944015449
12.62533837.518394

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.