3" HDPE mortar tube question

[FinnAmerican]

I never posted on this Display section before. But I post on behalf of my friend.
My Pyro buddy (licensed) wants to know what the inner diameter of a 3 inch display shell tube should be: 3.0" or 3.05". He asks this because he's come across a few websites that sell either ID 3.0" or 3.05" tubes.
He's been checking out HDPE tubes online and wasn't sure of the appropriate inner diameter. He would appreciate any help. All that he is sure of is the length should be 18".

[rfgonzo]

Mine are all 3-5/64 ID by 24 long

[Mattp]

i really dont think .05 of an inch is going to make a difference at all....thats less then 1/16 of an inch difference .. i dont think every shell is perfectly the same size either ... so really should be fine.... if a legit place sells them already plugged for the use of fireworks... im sure they are fine to use ... and yes for 3" shell the minimum length is 18"... but can be longer too

[d34d3ND]

ID of HDPE is not perfect and just as Mattp said not "every shell is perfectly the same size either". You are really looking for 3 things when it comes to sizing of HDPE. The first is assuming that a 3" shell is going to be a minimum of 3" in diameter. Yes, there are variances, but you wont know that until you actually have the shells and place them in the tube. So, you want to pick HDPE with an ID of at least 3". This means you would be using DR 15.5 (3.021 ID) or DR 17 (3.064 ID). Again, HDPE Fusion pipe is not 100% accurate, these are averages. The second thing you need to look at it is if the pipe can contain the pressure. DR15.5 is rate at 110 psi and DR17 is rated at 100 psi. I dont have the website saved, but I found that the peak pressure of a 3" shell is about 41 psi. So, this comes down to both pipes will work since we have the pressure and the size. Last, is going to be availability. DR 15.5 is NOT a common size of pipe. You will have a heck of a time finding it. DR17 is much much more common on sites that sell premade mortar tubes as well as if you were going to make your own and buy the pipe from a supply house.

What it all comes down to is you want to purchase 3" HDPE DR 17. This meets all the criteria and, if you are looking at some of the sites out there that sell the mortars premade, this is what you will find. I just added a lot of words to say what rfgonzo and Mattp did.

[AquaticPyro]

I agree, it is not the precise. 1.81 vs 1.91 can matter but to be safe get the DR17 3.05 since more will be likely to fit of it is close. You will still get plenty of lift if it only that much bigger. If it is like DR9 and DR11 they both have the same outer dimension and can be swapped for each other on rack anyway.