Composite materials for pressure applications.
Composite materials for pressure applications.
(OP)
Hello all.
I've just started a new job and my first task is to investigate using composite materials in place of the current aluminium choice for some tubes with an internal pressure of 16 Bar.G @ 5degC and 0 Bar.G @ 260degC. Tubes are approximately 4" in diameter and upwards of 100" long.
I've not got much experience with these materials and wondered if any of you guys had any links or information resources to help me with my research.
Thanks in advance,
Lee
I've just started a new job and my first task is to investigate using composite materials in place of the current aluminium choice for some tubes with an internal pressure of 16 Bar.G @ 5degC and 0 Bar.G @ 260degC. Tubes are approximately 4" in diameter and upwards of 100" long.
I've not got much experience with these materials and wondered if any of you guys had any links or information resources to help me with my research.
Thanks in advance,
Lee





RE: Composite materials for pressure applications.
Essentially, this sounds like the ideal application for a filament-wound product. Not knowing anything about your application, a wound glass or carbon tube 'should' be able to get you the pressure requirement without much hassle.
The temperature requirement pushes the general envelope on common resins systems. I can't help you there. If weight isn't a major issue (if this pipe isn't a fly-away part) Basalt fibers will tolerate 500 F without a problem, and their pricing is between E-glass and S-glass, last I was aware.
http://www.mccleananderson.com/would be one place to start your research.
RE: Composite materials for pressure applications.
yes a filament winding would be a cost effect manufactuirng process for making such tubes. But, if your design requires bending stiffness along the axis of the tube, filament winding may not get you there since zero degree plies can't be wound with this process. Additionally, material considerations should be made in regards to the working fluid and temperatures since composite properties are degraded when they are subjected to high moisture and temperature (i.e hot wet conditions). Mil handbook 17 may have some properties to help you but such properties are from flat panels, not wound tubes...
RE: Composite materials for pressure applications.
Weight saving is the primary objective. Items are to be used on vehicle systems and hence vibration etc will be an issue. The items will be held rigid in vertical position and bending stiffness would not be a requirement.
Regards,
Lee
RE: Composite materials for pressure applications.
www.braider.com might give further pointers.
If longitudinal stiffness to handle vibration is not an issue, then, yes, a popular option would be filament winding with any of the major fibers, with a cost/weight trade off according to fiber material.
(As MechanicalChef said, E-glass, basalt and S-glass are all good options, with carbon as a distinctly higher priced option, although it would probably minimise weight. Basalt fibres have been getting more publicity recently, and may increasingly compete with glass.)
Also as MechanicalChef said, a major problem here could be the service temperature of 260 deg C, albeit lightly loaded. Getting a polymer matrix which can handle this is no great problem, but it will tend to increase costs and reduce flexibility. I think a BMI (bismaleimide) would be the best bet, but a phenolic might do it. Hexcel and Cytec will have candidates; 3M is also worth a try, as are Magnolia Plastics and YLA Inc. There are also a number of polyimide (PI) options around these days. They're still pricey, but could certainly handle the temperature. Unitech LLC and UBE both have a fair amount of publicity out there for their PI-type resins.
I'm probably a bit too aerospace biased to be any more precise.
Not sure how many expert pressure vessel composites people visit here; perhaps a more pressure vessel-related forum might give you more response.
RE: Composite materials for pressure applications.
We've started some material suppliers off looking at potential options for the application. They are not far from a proposed material solution now, so things are going well on that front - I will be picking their brains for design tips, rules when they come back to me.
With that in mind, the things I'm starting to consider now are assembly techniques of the various composite components. I know that machining, cutting and drilling can be acheived with some materials, but that you weaken the structure if this is done incorrectly or too much. Do you or anyone else know if there are any good reference books or guidelines out there for designing and assembling composite components - its looking like a bit of a black art to me at the moment......can aluminium flange plates etc be overmoulded into the composite mix at all??
Regards,
Lee
RE: Composite materials for pressure applications.
Pressure vessels are usually made by filament winding. The winding tension is probably an important part of material performance. Braiding could work but the fibers cannot be applied with tension and there are other issues that make it less commonly used for pressure vessels.
260C is at the upper limit of most BMI's and polyimides. Fibraplex has the lowest cost BMI's available at $40 to $50 per pound and they have a BMI with a Tg of 370C.
http://www.fibraplex.com/news.htm
The biggest problem with including metal inserts is the difference in coefficient of thermal expansion between materials and the very large temperature range the part will see during cure or in use. It requires very careful design and material selection. If you can manage to include all your details into a fiber preform and then resin infuse the part using RTM or VARTM you can avoid a lot of problems and cost.
RE: Composite materials for pressure applications.
Regarding assemby/fastening, a natural element of filament winding is a fiber build-up at the ends (the turnaround region). While I don't have a great feel for stress and limits to drilling composite, instead of sawing off and disposing of those areas, it might be possible to utilize a portion of it as it is is a buildup. I don't know the feasibility of doing that for this application. Just a thought.