37 replies to this topic

[bigtonyicu]

Hi Everyone,

I live in Ottawa Canada, and am having a VERY hard time tracking down HDPE pipe for use as mortars, I only found 1 plumbing supplier that could order it and fell down when he quoted me the price, close to 90$/foot. All the water mains are run in PVC (schedual 80) so that's not an option, the gas lines run in MDPE I know it's not the same thing as HDPE, but could it be used?

MDPE pipe manufacturer rates it at 80 PSI (DR11)

I open to other ideas,

I don't want to use steel but I kind of feel like my back is against the wall.

Please help

[marble]

I have been told that PVC in a large bucket of sand is OK, don't quote me on that one though.

[Daedalus]

I have been told that PVC in a large bucket of sand is OK, don't quote me on that one though.

Only because the bucket of sand will catch most of the shrapnel. PVC is not an impact resistant plastic and can easily shatter. Have a look at pyrouniverse for some information on mortar racks. Not that I do any Cat 4 / EX stuff so can't comment from practical pyro experience - I wouldnt use PVC as I have seen how it can shatter from treading on bits of gutter etc.

[portfire]

Yes PVC is out of the question.

I think you'll be ok with MDPE.

From Wiki

"MDPE is defined by a density range of 0.926–0.940 g/cm3. MDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. MDPE has good shock and drop resistance properties. It also is less notch sensitive than HDPE, stress cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw "


"HDPE is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium catalysts or Ziegler-Natta catalysts) and reaction conditions. HDPE is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water"

[bigtonyicu]

I figured the characteristic would be close but the tensile strength might differ, What's the PSI rating on the HDPE mortars, say 3 and 4 inch" wall thickness would be nice to know also.

[Bonny]

The 80 PSI pressure rating seems kind of low. What size mortars are you making? For 1" mortars I have for shooting comets I use HDPE that is rated to 160psi. I fire all of my 1" shells from steel mortars. Once I get into larger shell though I will be using paper tubes or HDPE.

[bigtonyicu]

The 80 PSI pressure rating seems kind of low. What size mortars are you making? For 1" mortars I have for shooting comets I use HDPE that is rated to 160psi. I fire all of my 1" shells from steel mortars. Once I get into larger shell though I will be using paper tubes or HDPE.

I'm looking for 3" and 4" inch

[Bonny]

I'm looking for 3" and 4" inch

I think the pressure rating is way too low to fire shells that size. If you can't find anything more suitable, try carpet shops or something and get some heavy paper/cardboard tubes. You should be able to find wall thicknesses of 3/8" or more. If you are in Ottawa, you should be able to find some good, heavy HDPE somewhere, but you might have to go to the Toronto area.

[portfire]

I found this which my be of some help

http://www.javelinir...ipe_systems.htm

[bigtonyicu]

Bonny, you're from Canada, I'm open to sugestion on where to look for HDPE, like I said above plumbing suplys was rediculous, and Oxford Plastics Inc. "the only canadian manufacturer" I could find hasn't return my emails.

Do you have any? if so where did you get it, I have no problem driving to Toronto to buy some I just can't seam to track it down

[Bonny]

Bonny, you're from Canada, I'm open to sugestion on where to look for HDPE, like I said above plumbing suplys was rediculous, and Oxford Plastics Inc. "the only canadian manufacturer" I could find hasn't return my emails.

Do you have any? if so where did you get it, I have no problem driving to Toronto to buy some I just can't seam to track it down

I am indeed from Canada, but nowhere near Ottawa or TO, I have a source , but it's not likely you'll be driving to the Prairies for some pipe.

Although these are manufacturers, they may be able to point you to a distributor. Try these places:
http://www.polytubes...=...5&Itemid=93
http://www.ic.gc.ca/...mp;naics=326122
http://www.ipexinc.c...olyethylene.asp

You should figure out what you need first though, length, wall thickness etc.

Good luck!

[digger]

The 80 PSI pressure rating seems kind of low. What size mortars are you making? For 1" mortars I have for shooting comets I use HDPE that is rated to 160psi. I fire all of my 1" shells from steel mortars. Once I get into larger shell though I will be using paper tubes or HDPE.

One thing to remember with pipe pressure ratings is that they are rated for continuous use, infinite length and pressure cycling over a long period of time. The burst pressure will be far higher than this. It should be possible to calculate the burst pressure given the material properties and the dimensions of the tube (plus mdpe will have quite some ductile range). If the worst comes to the worst I can look up the properties in tables and calc the burst pressure for you if you give me some pipe dimensions (I assume tube dimensions are to ASME code).

Consider a shotgun, the tube wall would be about 4mm (educated guess from experience so no precise answers please) thick if it had to maintain the instantaneous pressure created when fired.

Edited by digger, 23 April 2008 - 09:48 PM.

[richard2]

Hi

I have used both 2 and 4 inch yellow MDPE gas pipe each with a wall thickness of around 7mm. I have never had a problem with the 2 inch even with fairly heavy cylinders and quite large amounts of lift to get them very high. However I did have a four inch fail when attempting a liquid fireball however this was probably my own fault as I added a teaspoon of flash to what was probably an already sufficient 80g of BP. The mortar was burried and no harm was done however after failure it remained in one single piece with a tear along the entire length. From this I would conclude that it is safer than the PVC as it is less likely to shatter. You will still have to do some tests with dummies to check that it is thick enough to withstand the lift of your shells.

Regards


Rich

[digger]

However I did have a four inch fail when attempting a liquid fireball however this was probably my own fault as I added a teaspoon of flash to what was probably an already sufficient 80g of B.

Yep that should do it as flash changes the nature of the burn significantly as you know.

We use an insert for a tank barrel for battlefield simulations. The insert consists of three steel tubes welded together to give three shots. To hold the insert in position there is a steel ring welded around the top. We used BP for these inserts, however we moved to adding about 2g of flash to improve the report. after the first firing (three shots) we inspected the insert and it had ripped off the steel support ring and forced the tubes closer to the breach (the steel ring was 6mm thick!!).

[pyrotrev]

MDPE with SDR 11 (diameter is 11 x wall thickness) is fine for firing round shells as long as you do a proper job on the bung in the bottom - some will say it's even a preferred material for salutes since it tend to "fail soft".The only drawback is weight, you're probably looking at 40...50% heavier than HDPE.