ABS Pipe Failure (Hot Water Service)

[briand2]

I am involved with a situation where some ABS pipes have failed. Most of the failures appear to be cracks starting at the end of the pipe inside solvent-welded fittings, especially couplings. The cracks run from the end of the pipe, along the section of pipe inside the fitting, and then another inch or so away from the edge of the fitting.

The service is domestic hot water (about 3barg, 65 degC).

Some people have suggested that this failure is due to either improper joint making (not chamfering the ends of the pipe, using too much solvent cement, etc). Others say it could be that the coupling has been tightened before the solvent-welded joint has cured fully.

Does anyone have views to support these statements, or any alternative suggestions?

Thanks in advance for your help.

Brian

 

[CRG]

I have never specified ABS for domestic hot water. Typically if I spec plastic pipe for domestic hot water, CPVC is my choice. The reduced allowable pressure due to temperature restricts use of most plastic pipe for hot water piping. That being stated, the pressure rating of plastic pipe is temperature dependent, and creep is a problem. What specification was used for the ABS pipe? Does the installed pipe meet the specified temperature and pressure? Are you certain that the temperature and pressure of the system are what you describe? Mixing valve failure and water heater control problems can cause excessive temperature. Transient pressures are often higher than what is indicated during a pressure test.

 

[pennpoint]

I found ABS sch 80 pipe(green)used for Compressed Air ONLY systems in Mc Master-Carr Catalog. It states that its rated to 185psig at 100F. What it does not say is, what the de-rating factor is for 140F, which is its maximum temperature rating. Your at 149F +/-.
As CRG as stated above CPVC is most always specified for hot water service. 3/4" Sch 40 CPVC pipe rated at 400 psi at 73F is only good to 100psig at 180F.
I think you have exceeded the maximum operating temperature/pressure ratings.

Good Luck

pennpoint

 

[moltenmetal]

ABS is used for drainage, waste and ventilation piping here in Canada- it is not rated for use with domestic hot or cold water under pressure.

CPVC is a good alternative, as is crosslinked polyethylene (PEX) with crimp-clamped brass hose fittings- it's becoming a popular alternative to copper here.

 

[briand2]

Thanks to all for your input.

As far as I'm aware (although I've yet to get confirmation), the pipe was Class C "Durapipe", which is tabulated as having a maximum working pressure of 3barg at 60 degC. The (nominal, static) conditions at which it was working were probably just inside that.

My previous experience has been that ABS fails under "shock loading" (caused by water hammer, for instance); that may have been the problem here - I've got to do a little more investigation.

Brian

 

[CRG]

Was the pipe routing designed for thermal expansion (are there expansion loops)? If not, a significant load could be caused from the thermal expansion.

 

[pennpoint]

briand2
You are correct.. a search of "Durapipe" yealds the tech literature. 3barg @ 60C, but it drops off rather fast. Max. temperature is 70C.
I,d rather use something with a greater margin of safety.

Good Luck
pennpoint

 

[briand2]

pennpoint,

I too would rather use something "with a greater margin of safety"!!! However, I'm investigating failures on a system that I neither designed nor specified; I'm trying to get as many points of view as I can!!!

In particular, does anyone seriously believe that "excess solvent cement" could lead to these problems?

Regards,

Brian

 

[MikeHalloran]

In literature available at durapipe.co.uk, there is a caution that Durapipe ABS is attacked by Loctite, and some synthetic oils. They probably leach out the butadiene (the "B" in ABS) that gives ABS its impact resistance. Presumably so would the wrong solvent, or too much of the right one.

The "S" is for styrene, strong, cheap, and brittle.

Durapipe ABS seems to have EC approval for use in potable water systems up to 70C. That surprised me, because the "A" is for acrylonitrile, present "for chemical resistance". One synonym for acylonitrile is vinyl cyanide. It's fairly nasty stuff.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[moltenmetal]

Vinyl cyanide, vinylchloride- what's the dif? Both are carcinogens, and both are used as monomers in pipe approved for potable water service. There's carcinogenic acrylamide in french fries too. As Joe Jackson sang, "Everything gives you cancer..."

As to the efficacy of ABS as a pressure-bearing piping material, it's certainly easy to fabricate and widely used on this side of the pond for DWV service as I noted, but its use in pressure-bearing service is quite limited. PVC and CPVC are widely used, and the latter is good to 80 C at fairly considerable pressure. As is PEX.

 

[corrosionman]

Briand2 Could there be any trace elements of anything in the hot water that are being released by the heating maybe the water company use Chlorine as they do in U.K.

I do not think the temperature is to blame.

Is the flow rate high and causing cavitation at the acute changes of pipe diameter where it suddenly meets the pipe end inside the fitting. We had some very puzzling cracking in 2" water ABS lines last year the pipe was in a plant that made surfactants (soaps) and the atmosphere alone was sufficient to degrade the Class C ABS till it leaked. No physical contamination took place. I will send the report if you wish.

 

[MikeHalloran]

Trace elements? Good point. About 20 years ago our local water utility started adding something 'to prevent leaks'. I don't remember what it is.

I remember that our drinking water will now kill a goldfish in 8 hours or less.

I remember that our drinking water swells rubber parts so badly that seals and washers cannot be stuffed back into the cavities from which they are released, and, allowed to dry in air, shrink into bizarre shapes so the seals and such are not reusable.

I remember that our drinking water used to taste good.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[stanier]

Brian,

I have encountered failures where excess solvent cement has been applied to ABS piping by inexperienced tradesmen. The solvent cement actually ran down a length of sloping pipe.

Solvent cement is made up of 75% MEK and 25 % ABS resin. The chemical weld of a joint is formed by an interference fit of the pipe into the socket softened by this mix. The MEK diffuses through the material and evaporates leaving a homogeneous joint. If an excess of solvent weld is allowed to pool in the pipe it will weaken the parent material.

The failure you have described is more likely to be faulty product however excess solvent weld cannot be discounted.

The point made about high temepratures and waterhammer are unlikely to be the root cause. With high temepratures the modulus of ABS is significantly reduced hence the celerity and resultant pressure transient will be reduced. It will tend to behave much like a "garden hose" and adsorb and transients.

High temperature and pressures are unlikely to result in failure in a brittle mode in a thermoplastic such as ABS. A typical failure would be a short crack in the longitudinal direction and then the crack will turn at right angles around the circumference of the pipe.

ABS is approved for drinking water in Europe and SE Asia. Its compliance is without question. Its been tested in a number of internationally recognised laboratories.The reference to acrylonitrile shows ignorance. Salt is a compound of sodium & chlorine, neither element you put on your fish and chips. But of course the ABS manufactured to ASTM standards is a different material to that produced in the UK, Europe, Australia, Malaysia and Indonesia.

Here in Australia we use ABS up to DN800 in all manner of industries. It is used extensively for reverse osmosis plants and ultra pure water for the electronics industry. In Taiwan it is used in the manufacture of TV and computer monitors where high quality water is required.

 

[briand2]

Thanks very much to everyone who has contributed!

Tomorrow, I expect to see detailed explanations of the failures (including temperatures, pressures, grade of material, etc). I'll let you know what I find (and I'm sure I'll be looking for more comments!!).

Regards,

Brian