37 replies to this topic

[Pretty green flames]

Question, how can I determine that the pipe I have is HDPE (Or MDPE, doesn't matter). I got some pipe that i think is HDPE but i'm not sure, so is there any way to determine if it's really HDPE?

[portfire]

Question, how can I determine that the pipe I have is HDPE (Or MDPE, doesn't matter). I got some pipe that i think is HDPE but i'm not sure, so is there any way to determine if it's really HDPE?

Where did you get the pipe from PGF? If It's water pipe, (the type they use underground) my guess it will be HDPE.

I've found that cutting HDPE leaves small flakes and burs around the edge, which feels like binbag material (polyethylene ?) where as PVC has hard jagged fragments.

[Pretty green flames]

It's used as core material for PE/PVC foil.


Here's a picture of the pipe

[wjames]

with me being fairly newish to mortar....what kind of max pressure would you expect to see.....lets say on a 2" mortar.......yes i know that will depend solely on the volume of lift powder, but im just looking for a rough value. 5 bar ?


I understand that most people use plastic as opposed to steel......is this purely incase the shell goes off in the tube ??

im sure a thick walled seamless steel tube would outperform a plastic counterpart - but i presume there are reasons for not using it ???

[digger]

with me being fairly newish to mortar....what kind of max pressure would you expect to see.....lets say on a 2" mortar.......yes i know that will depend solely on the volume of lift powder, but im just looking for a rough value. 5 bar ?


I understand that most people use plastic as opposed to steel......is this purely incase the shell goes off in the tube ??

im sure a thick walled seamless steel tube would outperform a plastic counterpart - but i presume there are reasons for not using it ???

Basically yes seamless pipe would be far stronger than the plastics, but it is what happens if there is for instance a salute going off in it is the main concern. The last thing you want is steel shrapnel flying around. In some cases steel mortars are used in the case of large Maltese multi break shells, but these are fully buried as far as I am aware and then bunkered.

I am sure Karl Foxman will let us know the Maltese practices.

By the way I believe most MDPE is yellow and HDPE is black (but I stand to be corrected)

PGF is that pipe you have grey? If so it may be PVC which is to be avoided. You could try a drop of pvc glue or xylene on it to see if it melts the suface in which case it is PVC.

Edited by digger, 07 September 2008 - 04:05 PM.

[Pretty green flames]

PGF is that pipe you have grey? If so it may be PVC which is to be avoided. You could try a drop of pvc glue or xylene on it to see if it melts the suface in which case it is PVC.

Yes it's grey though I have seen all kinds of HDPE, black and yellow beeing the most common.

Ok I did some experimenting and here's what i've come up with:

Burn test

PP - Burns with a constant flame (Blue/Orange), no lampblack produced
HDPE - Burns with a constant flame (Blue/Orange), no lampblack produced
PVC - Burns with a bright orange flame producing quite a bit of lampblack



Ok, so basicly, cut a small piece of the material and set it on fire, if it produces lampblack it's a no go.
PP and HDPE hardly differ from each other when burnt, the only thing I did notice was the smell from the burned material. The burned PP didn't exactly smell of anything. while burning the HDPE it released a distinct sort of smell, I can't exactly describe it but it seems specific to HDPE.

Solvent test

Lacquer thinner was used (Mainly Xylene, some Toluene also)

PVC - Melts it right away
PP - No sign of damage
PE - No sign of damage

So basicly, you can eliminate PVC straight away but PP seems to be more of a challenge. I'll rely on my sense of smell for the moment, because the smell that the HDPE puts out is really distinct.

Thanks for the help Portfire & Digger

EDIT!: Something interesing i've observed, HDPE seems to burn with a flickering flame!

Edited by Pretty green flames, 07 September 2008 - 05:06 PM.

[digger]

Yes it's grey though I have seen all kinds of HDPE, black and yellow beeing the most common.

Ok I did some experimenting and here's what i've come up with:

Burn test

PP - Burns with a constant flame (Blue/Orange), no lampblack produced
HDPE - Burns with a constant flame (Blue/Orange), no lampblack produced
PVC - Burns with a bright orange flame producing quite a bit of lampblack

Ok, so basicly, cut a small piece of the material and set it on fire, if it produces lampblack it's a no go.
PP and HDPE hardly differ from each other when burnt, the only thing I did notice was the smell from the burned material. The burned PP didn't exactly smell of anything. while burning the HDPE it released a distinct sort of smell, I can't exactly describe it but it seems specific to HDPE.

Solvent test

Lacquer thinner was used (Mainly Xylene, some Toluene also)

PVC - Melts it right away
PP - No sign of damage
PE - No sign of damage

So basicly, you can eliminate PVC straight away but PP seems to be more of a challenge. I'll rely on my sense of smell for the moment, because the smell that the HDPE puts out is really distinct.

Thanks for the help Portfire & Digger

Wow some good testing there

[bigtonyicu]

I understand that most people use plastic as opposed to steel......is this purely incase the shell goes off in the tube ??

im sure a thick walled seamless steel tube would outperform a plastic counterpart - but i presume there are reasons for not using it ???

Actually Shimizu recommend that IF steel must be used, It should be seam welded with the seam facing away from the operator. That what if a shell were to fail, the seam opens up (it's the weak point) to vent the pressure. A cast or extruded pipe has no specific weak point it over pressurize the shatter.

Keep in mind that in the case of a salute it's not a case of pressure but shockwave; a KClO4 + Al makes not gas byproduct it's really a thermit reaction not a true combustion, since no gas is produce no seignifican't pressure is created, its the velocity of the shock wave that destroys the tube, not an over pressurizing.

[cooperman435]

Not wanting to argue against the great shimzu but if a seamed pipe split and vented through that split surely it would propel the tube towards the operator?

[digger]

Not wanting to argue against the great shimzu but if a seamed pipe split and vented through that split surely it would propel the tube towards the operator?

I agree with your logic, maybe he was hoping any small bits of shrapnel would fly away from the operator. However most welded pipe now has a weld efficiency of 1, hence it can not be guaranteed that it will split along the weld.

Maybe the cold products of flash are not gaseous but there stands a chance that the aluminium oxide is gaseous during the reaction as its boiling point is around 3000C. I have not checked the stoichiometry of flash reactions but at a guess the will be left over gasses at end of reaction. But it does stand to reason that the shock wave is a major contributer to failure.

Edited by digger, 07 September 2008 - 06:46 PM.

[Arthur Brown]

The whole point of MDPE and HDPE is that they fail soft and soften and stretch to destruction. PVC shatters easily to small shards which can fly a long way and still puncture the skin. Steel will shatter into small shrapnel if anything detonates in the tube.

[Arthur Brown]

There are two types of mortar in professional use in the UK GRP and HDPE/MDPE that's commercial one piece GRP mouldings with integral plug and gas/water main pipe with DIY plugs.

This is largely because these are the best current practise therefore insurance preferred Paper tubes are still in use but considered safe enough but not robust and very susceptible to dampness. Paper and GRP and H/MDPE are insurable for pro use. Steel mortars having a nigh injury fail mode need special care -probably full length burial. PVC is entirely UNsuitable for mortar use.

Edited by Arthur Brown, 07 September 2008 - 07:34 PM.

[bigtonyicu]

I agree with your logic, maybe he was hoping any small bits of shrapnel would fly away from the operator. However most welded pipe now has a weld efficiency of 1, hence it can not be guaranteed that it will split along the weld.

Maybe the cold products of flash are not gaseous but there stands a chance that the aluminium oxide is gaseous during the reaction as its boiling point is around 3000C. I have not checked the stoichiometry of flash reactions but at a guess the will be left over gasses at end of reaction. But it does stand to reason that the shock wave is a major contributer to failure.

I was thinking the reason to using the seam welded pipe was more that only 1 peace would be created most of the force is still directed downward; if the tubes did manage to fly, the high mass lower velocity and high drag would keep debris localised. But in any case, I agree, especially for Salutes no steel should EVER be used.

Actualy KClO4 reaction is only arround 2450C, the only gas product should be KCl

[wjames]

thanks for the replys guys.


all interesting stuff

[Bonny]

By the way I believe most MDPE is yellow and HDPE is black (but I stand to be corrected)

As with almost any plastics, the pipe could theoretically be any colour. I've personally only seen red and black HDPE mortars though.