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ABS

Pros :

1) Chemical resistance, so can stand up to the average weekender going crazy experimenting with every different thing that can be found in an aerosol can.

2) Light weight, even the weakest of us has no reason to heft and bear these devices.

3) Low cost, it can be obtained almost anywhere, in the correct dimensions.

4) High impact resistance. Pressurised ABS chambers can be dropped with no ill effects, hit with a hammer without damage, and used with faster burning fuel/oxidiser combinations than PVC.

5) Favourable failure characteristics; except at low temperatures, ABS will not shatter on failure like PVC, and will instead simply rip open, or tear in half in some cases if things like gauges or meters have been tapped through its walls.

Cons:

1) Rarely pressure rated. Pressure rated ABS is very difficult to acquire, and likely more expensive than just using steel pipe. However, solid wall SCH 40 DWV ABS makes an excellent material for barrels of pneumatics (it can repeatedly survive short spikes of several hundred psi) and combustion chambers for advanced propane combustions as well as oxygen enriched combustions. Cellular core ABS, while rare, should be avoided at all costs.

2) It's still plastic. Threaded joints with metal are dicey, and tapped threads will always weaken the pipe, by a factor of 4 or more. Use in high powered hybrids (this effect has been observed with 20x oxy/propane and higher mixes), where the combustion products are denser and have more heat capacity, can literally flash boil the pipe if it is used as a barrel, causing extreme deformation and usually destruction of even heavily reinforced designs. Bottom line - thick plastic is no substitute for metal in a hybrid, even if it has the same pressure capacity.

3) Decomposition products are nasty! If you have ever taken a whiff after firing it a few times, you will get a burning in your nose. This caustic gas is not good for you! Burning ABS produces a type of cyanide gas which is incredibly deadly (obviously).

PVC

Pros:

1 )Inexpensive, the pipe is almost free. Fittings are where the money is dropped, but well worth it

2) Multitude of dimensions to chose from. Pretty much any configuration of pipe fitting can be found somewhere in PVC, but get out your checkbook! 6" sch 80 will run you right around $40 for a 10' piece.

3) Pressure rated variety is easier to find than the ABS equivalent. What you see is what you get. The rated pressure on the side of the pipe is already conservative, so you don't need to incorporate safety factors, unless you want to. Fittings are always stronger than bulk pipe, as long as the glue joints are made and allowed to cure properly and are Schedule 40.

Cons:

1) Limited Chemical Resistance. Aldehydes and ketones are out, as these readily dissolve the polymer, as in a glue joint, just read the label on the can: Acetone, THF, MEK. Some fuels should be totally avoided such as carb cleaner and insect repellant as they decompose ABS.

2) More brittle than ABS, but by not using oxygen and just burning fuel and air....should never be a problem.

3) Cellular core PVC is common at many hardware/home improvement stores. Make sure you buy SCH 40 pipe with a pressure rating printed on the pipe. If the pipe is not specifically marked with a certain PSI rating (ie, 330 PSI, depending on diameter), IT IS NOT PRESSURE RATED!!

''Source taken from www.spudtech.com''

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