Problems in PVC & PVDF piping systems for sodium hypochlorite (bleach)
Q. This question may appear as a multiple part question, but it really addresses a single problem we are having with PVC glue / welded joints in a series of sodium hypochlorite PVC pipes.
1. Is it recommended to use regular Teflon tape to secure threaded PVC pipe and fittings or is there a similar product that can withstand the high
acidity^alkalinity and corrosiveness of sodium hypochlorite ?
2. For glue welded connections, is PVC primer and glue, that is typically used for PVC pipes to carry water and waste water strong enough to withstand the corrosiveness of sodium hypochlorite ?
We have noticed that many of our leaks are occurring at the glued joints and sometimes at the threaded joints. Any one in a similar industry ? How do you weld PVC pipe together? We use Sch. 80 PVCDan C wastewater treatment - Brooklyn, New York
A. Hi Dan!
Firstly, please see the fin.com library pages wherein there's an article about Leaking On The Job ... all about PVC cementing.
This doesn't cover threaded connections using TFE tape. Going by memory, we used to dry fit the threaded connection, count the number of 'turns' that were needed till one couldn't turn any more, then add the tape, then add on two (or was it 1-1/2?) more turns.
In Ye Olden Days I recall taping a 1/2" fitting and turning and turning and breaking the female end due to the enormous lubricity that the tape gave ... & that was by hand !
Don't worry about the cement being affected by hypochlorite ... 'tis the procedure that was wrong.
I hope that this will help you ... & let us know if it does.
A. Check this link out. It might help. http://www.finishing.com/library/cementingPVC.html
A. PVC, and the glue used to make joints, can fail after long exposure to highly alkaline chemicals (like hypochlorite, which is alkaline, not acid). You can use polypropylene pipe or tubing, or stainless steel.
Hi again Dan,
What Jeffrey says may be true ... I don't know ... but I do know that PROFESSIONALS, such as we, as top notch thermoplastic fabricators were, never to my knowledge had this problem.
But when we encountered a 'nasty' condition, such as 93% sulphuric or strongish nitric, we would add a weld bead to the joint.
Particularly on larger pipe & fittings, when you cement them, there is a minuscule gap which the cement is supposed to fill. If, after one year, you were to cut open a cemented 10" dia fitting in half, you could see the cemented line ... and with your finger nail, you could indent it very slightly, too ... but that's with large fittings.
The proper PVC cement will fill up the gap successfully.
But Jeffrey, you said use stainless for alkalies. Yuck. Yes, PP would be OK but the cost of buying it and the cost of installing it would be much higher ... and unless UV pigmented, then outdoors it would be nbg.
- White Rock, British Columbia, Canada
A. I've been wrestling with this problem for many years, mostly in trying to fix problems created before I became involved.
The only product I have ever found to be suitable for use with the hypochlorites is IPS Weld-On 724. Last summer I spoke with the folks at Oatey to see if they had anything suitable and they offered 31113, 31114, & 31115. Later, I downloaded the MSD sheet and that document specifically states that the Oatey product is incompatible with "Acids, oxidizing materials, alkalis, chlorinated inorganics (potassium, calcium and sodium hypochlorite), copper or copper alloys."
My understanding is that the problem becomes more apparent on larger diameter pipes because the glues for larger diameter pipes have "inert" filler materials that are intended to fill the (larger) gap on these fittings. Apparently, the chlorinated compounds attack the filler materials leading to joint failure. However, I've seen 1/2" thru 2" pipe fail due to incorrect cement as well.
A. Last summer, I worked with a contractor to salvage a rework project on which they used Oatey 31015, specifically not approved for this service. A contact of mine with a company that makes sodium hypochlorite generation systems steered me to 3M Scotch-Weld Acrylic Structural Plastic, Part Number DP8005 =>
After the joint is made with the wrong sealant, you can place this over the top of the joint and it is supposed to make the joint leak tight. You just clean off the excess primer & glue before applying the 3M product. I haven't checked back with that client to glean how well things are performing, but since they are not calling me, I'd say that bodes well.
3M Acrylic Structural Adhesive
I happen to be looking for alternatives to the IPS product I noted above and this thread caught my eye. I have another project kicking off and I like to have more than one alternative in the specs. If any of you know of anything, please let me know.Damien Stella
- Anchorage, Alaska
A. In my opinion, uPVC Pipe with EPDM rubber ring joint for straight connection and k-Type socket PU coated Ductile Iron Fitting for Bends will solve the problem.
I welcome your opinion on this solution. Classical Solvent Cement Joint cannot easily react with heat expansion and other vibration factors.
- KL, Malaysia
February 26, 2008
A. When dealing with bleach (sodium hypochlorite) of 9-15% concentration its always best practice to follow the manufacturers specific instructions to the letter while making the solvent welded joints to include cure times. When pressurizing the bleach, don't get excessive or you can expect to have many leaks as it will eventually eat the glue. Also, avoid threaded connections like a heart attack! Teflon tape will hold on a no/low pressure threaded connection, but I have found that a simple hobby glue called E-6000 =>
- Burlington, Kansas
April 10, 2009
Q. To Chris Smith in Kansas: Can you provide examples of where you have you used the E6000 adhesive in a 12% hypochlorite application? How long have these systems been in service without leaks? I have a project coming along that will involve trade solution product and I'd like to have some evidence to offer the client before I propose using a product not generally considered for use in this industry.Damien Stella [returning]
- Anchorage, Alaska
April 13, 2009
A. Damien Stella, I work with 10% and 12.5% Bleach solutions on a daily basis doing water treatment for Wolf Creek Nuclear Power Plant. We routinely used E-6000 on all threaded PVC and plastic pipe joints in our old Bromination system as the pressure that we had to over come was approximately 150 PSI. we saw far fewer leaks from the threaded joints using this hobby adhesive than any other thread sealing compound that we could get on the market. we have a newer system installed now that is a low pressure Neat feed system that injects chemical at less than 5 psi and the E-6000 is still in use as we have found it to be the proven to not leak. we also no longer use diaphragm pumps as they would literally hammer the system to a point where it would leak. our new pumps are gear driven PULSAFEEDER Eclipse series pumps.
Also, if money is not an issue with your upcoming project, you might check into socket thermo welded Kynar plastics, the Kynar (PVDF) pipe is currently used on our system for the delivery piping and when thermally welded correctly will not leak because the plastic for both the male and female parts of the joint are melted and then pressed together bonding them permanently. hope this helpsChris Smith [returning]
- Burlington, Kansas
November 1, 2010
Q. Chris Smith, have you actually installed the PVDF systems and placed them in service? A couple of years ago, I read good things about PVDF, then more recently learned of severe failures.
Would appreciate knowing your experience with that.
- Anchorage, Alaska, USA
November 10, 2011
A. Here is my 2 cents worth, my company has been involved with the installation of any number of chemical systems requiring piping fabrication and can advise the following.
If you pipe a Hypochlorite system in metal it is only short term compatible with either Titanium or Tantalum anything else will just dissolve very quickly.
With regards to making a long term strong Solvent Welded joint on PVC-U use a product made by Tangit called Dytex using both the Solvent and Adhesive. We have done many strong Acid & Alkaline systems with excellent results.
The trick is to ensure you follow the process to the letter for the best long term results, we have found that the US grade of schedule 80 pipe and fittings gives the best results over the metric equivalent as this has proven to have some issues.
Hope this helps.
In answer to your query about PVD-F material we use this material extensively and have found it to be utterly reliable. The last major project involved Hydrofluoric acid at 95% concentration to a 10 kl storage tank and then to a distribution mixing tank farm.
This system has been in approximately 5 years with a continuous vacuum alarm system as all the piping runs outside the decanting room are in Double containment.
We perform yearly pressure tests on the outer containment system +GF+ Contain-It Plus and no issues have been detected, this system is in daily use.
We have also just recently completed an UltraPure water system at a NANO facility that uses heat sanitization fully IR Welded fabrication and Triclover joints without any issues.
Again the trick is to follow the process to the letter for the best results, with failures I have been asked to investigate over the years 98% of the time it is Installer error without doubt.
The smallest seemingly insignificant oversight can mean a complete failure of the system as a result; think twice act once is what I always tell my guys.
- Melbourne, Australia
March 3, 2012
Q. Good day to all... can help me to know if possible to glue the PVDF materials. Thank you.Freddie Andico
- Manila, Philippines
March 6, 2012
A. Hi Freddie.
I think the implication of Chris Smith's posting was that thermal socket welding is possible but gluing isn't.
Ted Mooney, P.E. RET
Brick, New Jersey
A. Responding to many of the questions posed about PVC and PVDF used in transport or storage of sodium hypochlorite.
PVC as a material is in fact resistant to high concentrations of NaOCl. Leaks occur at the joints where glue is used. The industry has developed special formulations of glue for use with bleach, but the lifetime expectancy is still low.
Tank fabricators typically do not use glued joints since they are making open top or vented storage tanks out of sheet (like plywood) for bulk storage. The fabricators heat weld the joints using an extrusion gun which is similar to a glue gun; it heats up PVC rod which is fed into the gun, then extruded over the two joining pieces. The thermally fused bond is now resistant. This is not recommended for pipe installations because the cooling time of PVC is too quick and the chlorine gasses that are put off can be hazardous to your health.
PVDF is also a temporary (and costly) solution for transportation of bleach, as the material is broken down by the bleach.
Polyethylene (PE) can be used for such transport. My company manufacturers a PE piping system for transport of high concentrations of sodium hypo. The product is called Chem Proline. Not all PE can be used for NaOCl. Certain resin advances have allowed us to engineer this product specifically for use in bleaching applications. PE pipe is joined similar to PVDF, using heat and not glue.
Thermally fused PE is a fairly inexpensive product. Mechanical joints (threads) should be avoided as well. PVC or PVDF or PE will all tend to leak at the mechanical connections, regardless of how much PTFE tape you use. Permanent installation methods such as heat fusing should be used whenever possible to keep the integrity of the piping system.
- Malden, Mass, USA
March 5, 2013
Q. In reading your responses, do you have a recommendation for a thread sealant. I have a 1" kynar water educator that is connected to a domestic water line. When the domestic line is opened it will suction a 93% sulfuric acid solution into the system to control the ph level. The suction fitting is a Sch. 80 PVC male adapter. We have tried different teflon tapes to wrap the threads, but as soon as the system shuts down a leak occurs at the threaded connection. Any advice?
- Texas USA
A. I installed a T-Chlor system with schedule 80 PVC and called Oatey to ask about what type of cement to use for sodium hypochlorite. They told me to use EP42 (Oatey # O30329 Lovoc Gray Cement).
As a side note I bought a stick of CPVC pipe to use because the plumbing supply place didn't have any schedule 80 PVC. They said it would work with the schedule 80 fittings. I mentioned that to Oatey and they said definitely do not use it with schedule 80 PVC fittings.
- Elk Mountain, Wyoming, USA