Anchor for Continuous Vacuum Piping

Vacuum insulated piping has been used for transporting Cryogenic fluids for many years now, and is the most common method for land based transportation of cryogenic fluids. The main challenges of transporting cryogenic fluids, namely heat ingress into the cryogenic fluid, and thermal contractions in the piping itself, are solved by the use of vacuum insulated or jacketed piping, however installation requires considerable knowledge and experience, and it can be extremely expensive to produce depending on the vacuum levels required.

The static vacuum is applied during production and must then remain complete in the entirety of the operating life of the vacuum insulated piping. Many of the materials used are quite standard, but may often require specific finishes and production processes in order to ensure the quality of the vacuum. which makes it a complicated and expensive product. Further-more there are limited number of enterprises that are able to successfully complete long and complex section of vacuum insulated piping.

AF Pipes has been specialising in double wall piping and double wall pipes for many years now, and the double wall pipe products of AF Pipes have been extremely well applied, operating trouble-free for many years of service in many marine, offshore, and land based installations. One of the particular challenges in the marine and offshore segments are the vibrations associated with propeller, engine, hull, and wave movements. The AF Flex system for double wall pipes is specifically designed to handle these vibrations in the piping, and at present is the most robust way of dealing with damaging vibrations. Unfortunately vacuum insulated piping was not designed for the harsh environment, and consequently is potentially damaged when exposed to the high amplitude vibration conditions. This can result in damage to the piping modules or module connections, and subsequent failure of the supporting mechanisms of the inner and outer pipe, compromising the integrity of the vacuum itself. As previously mentioned, the static vacuum is applied at factory, so if the vacuum fails during service there is no way to recover the vacuum without replacing the failed modules. Failure of the vacuum could be critical depending on the circumstances, and level of redundancy available.

AF Flex double pipe is often used as a closed system (with closed annular space for pressure detection), so it comes naturally for AF Pipes to investigate  and recommend a reliable and cost-effective method of applying the vacuum to the AF Flex system in order that the AF Flex double pipes can also be used with the vacuum system up to certain vacuum levels, without many additional measures to be taken.  Therefore AF Pipes has designed an alternative method to producing vacuum piping, with continuous vacuum piping. This is a complete vacuum throughout the entire piping arrangement, instead of separate static vacuum modules, and the vacuum is applied on site at the end of the installation. 

The introduction of the AF Flex anchor Cryo enables this concept. The anchor is an insulated fixed piping support point between the inner and outer pipe which allows a fixing point of the inner pipe relative to the outer pipe. This method has been available for some time for non-cryogenic fluids, but now the anchor has been developed for cryogenic fluids, with an insulated fixing block between the inner and outer pipe. The use of such an anchor is particularly relevant with cryogenic fluids, due to the large thermal contractions that will occur when using standard stainless steel piping with cryogenic fluids. The purpose of the anchor is to provide fixing points in the piping arrangement whereby the inner pipe movements can be controlled around these points. This must be analysed carefully during the pipe stress analysis, and ensure that the nozzle loadings on the anchor are within the specification. The flex anchors are validated during testing, and provided with axial loading, bending and torsional moment specifications.  When used in conjunction with the AF Flex supports, which are also cryogenic insulators with specified loadings and displacements, it is therefore possible to design an entire piping arrangement for cryogenic vacuum use with the AF Flex double wall piping system.

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