uPVC Pipe Chemical Attack? 4

[IBechir]

Greetings All

For uPVC drainage pipes and fittings to BS EN 1329, are there any chemicals that can be flushed down the toilet that can weaken the pipes/fittings? Many things can be flushed down the toilet but I had the peculiar experience of a specific soil riser, in a residential tower, that always fails at the bottom (the last elbow at the bottom).

The elbow is long-sweep 90', velocity breakers are in place, and vent pipe is connected. Also we made sure that the fitting is not forced into position (undue stresses) between the vertical and horizontal pipes. The fitting has a BSI Kitemark, and is from a reputable manufacturer, so I don't think its the quality of the fitting. I understand that uPVC has great chemical resistance but I am not ruling out that the damage may have been caused by chemical.

Much obliged for any information.

 

[btrueblood]

from

http://www.pvc.org/en/p/pvcs-physical-properties:

" PVC swells or dissolves in aromatic hydrocarbons, ketones, and cyclic ethers"

- acetone, MEK, toluene, benzene. Basically paint thinners. Oh, and nail polish remover. Somebody cooking illegal drugs may flush a fair amount of them; the odor would be a pretty good give-away.

 

[rconner]

To follow up the good response of btrueblood, while it doesn't mean necessarily that is what is responsible for your failure(s?), the answer to your question is YES (many chemicals have effects on most common plastics, including pvc). A perhaps extreme example of this is the glue or solvent cement itself that near immediately dissolves at least a surface layer of solvent-cemented joint pipes and fittings in the field installation process. Furthermore, other factors can play a part e.g. temperature/heat and specific concentrations or mixes of chemicals, and/or concentrations thereof etc. I think you will find from a quick internet search some manufacturers appear to be more careful, specific, and/or upfront about the exposure limitations and recommendations of their pipes (e.g. in comparing chemical resistance or application charts therefrom) than others. Notice that in the charts from a manufacturer at who appears to be even targeting specifically laboratory drain applications (with a quite chemical and heat resistant type of pvc, i.e. cpvc as opposed to upvc), where there is a likelihood at times of a great many different "chemicals" coming down the piping, that even in that case many specific "chemicals" are "NR" (meaning not recommended).
All that being said, I am curious when the ell, or fragments thereof?, are examined after failure(s?) does the plastic appear affected in any fashion, or does it look and feel (and if probed with a knife etc.) pretty much like normal new plastic pipe? Also, are there any abnormal chemical etc. smells (other than what one would expect, and the afficionados of the trade affectionately refer to as the the "odor of money" from what we all know is most normally "flushed"?) Also, while I see that apparently some type of velocity breakers are in place, do you know what the ​flow ​velocity is in that lowest ell (does it accumulate ​e.g. ​flow from the entire structure i.e. highest velocity​ when the tv goes to commercials​?​)​ As far as pvc as opposed to alternatives e.g. for tall buildings, I have seen that some architects and Engineers have used traditional materials for even new, quite tall buildings. Some of the reasons could be beyond stubbornness as revealed from a manufacturer, who incidentally I believe sells both types of piping, at​ ​

http://www.charlottepipe.com/Documents/InTheNews/CPF_Value_Engineering_Brochure_R2.pdf.

Also, while I guess the timing of your inquiry may be coincidental it is about the same time many of us in the USA have been plunged into this "polar vortex", I nevertheless noticed that from the latter link one has to be very careful with the pvc drainage pipe as to how temperature variations are handled, and I guess it is possible that may prove most challenging where relatively long lengths of piping and ells etc. are involved and that may not exactly be at all times at constant temperature (is there any possibility thermal expansion and/or contraction have come to bear on the change of direction/ell, say in wishbone/"pully" bone fashion, either with high magnitude of combined/bending or fatigue stresses?)

 

[bimr]

Nothing in the household should damage uPVC except for heat.

Is the pipe adjacent to a source of heat or cold in the room where the pipe is failing?

What is the mechanism of failure?

 

[IBechir]

The pipe is not close to any source of heat. I think the inner surface and color of the broken fittings are unchanged, I'll double check. The mechanism of failure looks like impact immediately at the bottom of the straight. I attached a photo, its not very clear, but the drainage pipe slopes down in the opposite direction to the red sprinkler branch and the light blue color in the background is the fire-sealant at the bottom of the shaft. We're planning to replace it with an HDPE fitting long-sweep 90' elbow.

 

[weldstan]

There are lots of solids in sewage and the ell could readily be seeing solids impingement at high velocity from sewage in a high rise residential tower. Wear is the most likely cause.

People will also flush solvents like those provided by btrueblood down the drain as well.

 

[bimr]

It appears that there is some type of water hammer causing the breakage. See the discussion in the link. Falling water may drop at speeds of approximately 10 ft/sec.

You might note that PVC is brittle at low temperatures. You have not mentioned low temperatures.

 

[bimr]

Try to repost the image.

 

[IBechir]

Reposting the photo. Temperature is 27-30'C range. I checked the inside of the broken fittings today and there is no change in color or surface texture. Its probably impact.