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How do you achieve the perfect seal?

How do you achieve the perfect seal?
Colin Chapman of Henkel, maker of Loctite brand products, provides insight into how modern technology overcomes an ancient and ever-present problem.

For as long as industry has used pipework, leaking joints have been an issue. That's because even with correctly machined pipe joints, minute surface irregularities in the thread flanks are enough to allow liquids or gases to escape from the assembled joint.

To overcome the problem a sealing method is required that can fill the spaces, no matter their size, by conforming completely to the thread surfaces of the pipe. One old favourite is PTFE tape. Benefits here include a high-quality initial seal, resistance to chemicals and solvents, and effective lubrication for the joint. However, the effect of lubrication can all too easily result in over-tightening of the threads, resulting in stress in the fitting which, in turn, can lead to potentially serious breakage. 

Not only that, shredding of the tape can readily clog filters and valves, leading to severe maintenance inconvenience. Pastes made from oils and fillers are also among the traditional methods of sealing the spiral leak paths of threaded joints. On the positive side, such pastes provide some lubrication for the joints, however they have poor solvent resistance, can ooze out under pressure and do not offer sealing on parallel threads. And where pastes are combined with hemp, the whole procedure can be extremely time consuming and messy.

Another established method of sealing pipe joints involves solvent-drying compounds. Like pastes, they can provide valuable lubrication, but these compounds will often shrink during the cure process. So, the traditional methods of sealing pipework leave much to be desired.

Cords are in fashion
Engineers who have used the traditional methods will quickly discover the switch to sealing cords is an easy transition. The thin fibres of the cord are simply wound around the male threads of the pipe for the recommended number of turns and then cut using the sharp in-built edge of the cord's container. That's all there is to it - and the joint is sealed in seconds. What's more, the fibres will not tear or shred to cause blockage. Loctite 55 - the sealing cord from Henkel - can be used on cast iron, steel, brass, copper, chrome, nickel-plated and galvanised surfaces, stainless steel and plastic, and is recognised through CORGI Certification approval. 

An alternative method of sealing joints with the added benefit of locking the fittings in place involves anaerobic sealants. Available in both liquid and semi-solid stick formulas, they cure in the absence of air - in other words, when the two threaded metal surfaces are brought together. The resultant joint is an insoluble and tough plastic seal that will thwart leakage no matter what pressure is applied. 

The anaerobic technology means that any excess sealant remaining outside of the threads will not cure, making it easy to wipe away and reducing the risk of contamination. Furthermore, the formulation of these products is such that any sealant left inside the joint will readily dissipate within the majority of fluid systems. And once fully cured, these sealants resist most industrial liquids and gases. 

But there is more: as previously stated there is an added benefit when it comes to using anaerobic adhesives for threadsealing. The adhesive technology means the same product also provides a threadlocking action that stops the sealed joint from loosening when subjected to shock or vibration.

To ensure an anaerobic sealant does all that is expected of it, the right grade should be selected for each application.  Indeed, there are six factors to consider when making the product selection - thread type, maximum pipe size, the fluid resistance required, disassembly requirements, time needed to achieve an effective seal and temperature requirements. On this last point, anaerobic threadsealants typically resist service temperatures from -55°C to +150°C. However, brief exposure to higher temperatures will not impair the sealing effect. 

To help users make the right choice, or to discuss general threadsealing principles, the technical department at the suppliers of such anaerobic sealants is an invaluable source of knowledge and advice.

Leaks may have been a fact of life in the past - but that need not be the case. There are up-to-the-minute answers to the age-old problem. Sealing cords are quick, clean and very cost effective. Anaerobic sealants give an economical way of preventing leakage with the added advantage of securely locking joints.
Henkel Loctite Adhesives Ltd

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