Double wall pipe support types

Double wall pipe support types – see new brochure here

We have experienced an increasing number of enquiries from customers within the recent months, for different sizes and types of double wall pipe supports, also from different industries that we have not expected to see. Consequently, we are very happy to say that the range of the AF Flex support for double wall pipe has been extended quite considerably. This is partly to accommodate the range of different sizes that have been requested, but also for somewhat unexpected applications that have arisen. As we are a relatively small firm with niche products, it is less complicated for us to develop new products and solutions extremely quickly, and then mature the product through our extensive in-house testing program.  This involvs a range of product specific tests that have evolved over time to reflect the environments in which the products are used. Which also means that should a customer have a request for a specific test, then we will be more than happy to oblige. The increased range of products does lead to the inevitable question however – “which inner pipe support type is most suitable for my application?”

You can now find a more detailed brochure for the AF Flex products, which covers the current range of types and sizes. The product brochure is available here on the website, and should be able to answer some of the questions, but in order to summarise, there are three different types of inner pipe supports in the AF Flex range:

  • Standard type: Historically used in the high pressure gas supply (ME-GI) double pipe system to provide a good balance of allowable radial deflection, and stiffness. This is also typically used on standard double wall pipe sizes where the schedules are larger than for low pressure systems, and whereby the standard design allows in such case for a larger radial deflection than the compact type.
  • Compact type: A further development on the standard type, using the same design concept in order to allow for smaller outer pipe sizes relative to inner pipe. Thereby reducing the weight and cost of the installation. This type is also best for the smallest pipe diameters, and can be made for outer pie sizes down to 1 “ in diameter. For sizes below this, then we would recommend that the AF Slim is considered.
  • Centraliser type: Developed for larger pipe diameters, where it was not possible to economically produce either the standard or compact type. This has a high stiffness, but limited radial deflection. Due to the small bearing surface area, and high stiffness, this is a very good choice for liquid, and cryogenic liquid piping. There are in fact two different designs for the centraliser, depending on the required outer pipe dimensions. The smallest gap (where NPS difference is only 2”) gives the stiffest, but least radially flexible design, which is only really recommended for axial displacements.

Typically the pipe support types and sizes are designed to give certain stiffness specifications, preferably to ensure dry mass deflection less than one millimeter. It may be apparent from some some specific sizes, that additional measures are necessary in order to achieve this general requirement, for example more frequent placing of supports. It is rather dependent on the acceptance criteria of the piping arrangement. In some cases two to three millilmetres of static deflection (without any loading) may be deemed acceptable. The deflection must also be considered in relation to the size of the piping being considered. The double wall piping arrangement must be stiff to the extent that it is not loose but, not too stiff as to overstress piping joints, connections, or the piping itself. This is unfortunately the most common cause of piping failure. It is also important to consider additional masses of the pipe, particularly when adding liquid mass to the pipe, in which case it may be preferable to use a stiffer model of support such as the centraliser type when dealing with long straight sections. A single or pair of standard type of supports could then be mounted around the bends, in order to take the radial deflection at the bend. This gives an example of how it is also possible to mix the different types of supports in order to provide the best possible double wall pipe installation.

We have detailed AF Flex design guidelines available for the design of the double wall pipe arrangement using the AF Flex double wall pipe supports, which if complied with, will cover most installations, without the need for extensive design resource. Please do not hesitate to contact me for a copy. For critical applications it is always recommended to run a pipe stress analysis, in which case the full range of load cases can be considered. For recommendations on the load cases, please contact us and we will gladly assist in this matter. Finally, and most importantly, by instigating the inner pipe support regime based on the stress analysis, the end user will be assured of a robust double wall pipe arrangement.

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