Protecting flexible metal components: why is it so important? After all, they’re made out of metal, right? Corrugated hose and metallic expansion joints are common ways to allow for flexibility in an otherwise inflexible piping system. The corrugations (also called “convolutions”) must change their shape as movements are encountered, providing the required flexibility to prevent damage to the piping system or the components attached to it. These corrugations must be very carefully designed and formed in order to provide the longest-lasting product with the highest cycle life. Additionally, the end fittings that are attached to these hoses and expansion joints must mate properly with the adjoining piping system, in order to provide a leak-free installation. Therefore, it is of vital importance to ensure that these flexible metallic components are not damaged during shipping, installation, or while in service.
If a corrugation on a hose or expansion joint becomes damaged, the performance of that corrugation is compromised. For example, if a corrugation is dented during shipping, the profile of the corrugation is changed. As bending stresses are applied to the corrugation, it cannot deflect as it was originally designed, and the bending stresses are typically concentrated where the metal has been creased by the dent (The photo left shows denting that can compromise the cycle life of a metal hose or expansion joint). This is called a “stress riser”, and the metal will fatigue most quickly at this point. For corrugated metal hose assemblies, an outer braid layer provides a measure of protection to the underlying corrugations, but sometimes additional protection is needed. During shipping, it is possible that flanged hose assemblies can move around in the shipping container, causing damage as they bump into adjacent hoses. Shipping these assemblies vertically might prevent them from rolling around, but the weight of the flanges can compress the hose during shipping, causing additional problems resulting from the baggy braid. This loosened braid applies excessive stresses to the corrugations when the installed hose is pressurized; the corrugations experience a burst of movement as they re-extend until the braid tightens back over the hose. To prevent this, hoses must be packaged carefully to avoid any damage during shipping.
With metal expansion joints, hardware (such as the addition of shipping bars) is often required to protect the unit during shipment and to prevent any movement of the bellows, which can reduce the remaining cycle life once the unit is placed into service. After the expansion joint is installed, these shipping bars must be removed in order for the bellows to deflect properly. Because expansion joints are offered in much larger diameters than hoses, isolating the bellows from movements and protecting the unit from shipping damage can be quite a challenge.
It is also important to prevent any damage to the end fittings on hoses and expansion joints. The sealing surfaces (pipe threads, flange faces, seats in tube fittings, etc.) must be kept free of any dents, scratches, or weld spatter in order to ensure a proper leak-free connection. While many companies use plastic thread caps to protect threaded fittings, our partners at Hose Master prefer a plastic mesh sleeve instead, which helps to keep the interior of the assembly properly ventilated during shipment, thus avoiding any moisture entrapment. Flange sealing surfaces often require specialized protective measures in order to keep the surface in compliance with applicable piping codes or customer specifications. Once the hoses/expansion joints are received, additional care must be taken when unpacking, handling, and installing them to prevent any damage. This is why Hose Master provides handling and installation instructions with every expansion joint that is shipped.
For metal expansion joints, there are also handling, installation, and safety recommendations published by EJMA (Expansion Joint Manufacturer’s Association). These recommendations can be found in their handbook “A Practical Guide to Expansion Joints”, which can be ordered from their website: www.ejma.org
Additionally, expansion joints may have special installation requirements depending on any obstructions surrounding the intended location of an expansion joint. In these circumstances, the expansion joint must be designed such that it can be partially disassembled in order to facilitate installation, then reassembled once in-place. It is critical that this reassembly is done in accordance with the engineered design of the unit, in order to prevent any excessive stresses to the expansion joint. Again, these special installation procedures would be included with the product.
It is important that flexible metal hoses and expansion joints are manufactured and fabricated using superior processes, in order to provide the longest-lasting products available. It is equally important to handle these items properly during shipping, handling, and installation to make sure they are able to provide maximum value.
The original article was written by Frank Caprio, Corporate Trainer at Hose Master.
For more information about selecting and protecting your metal hoses or expansion joints, contact Gallagher Fluid Seals today.