SWG install cancelled because I have a stainless steel filte

[mac4lyfe]

The installer just left without installing my Hayward Swimpure system. He said that they were instructed 6 months ago not to install SWG's with stainless steel filters (I have a nautilus - 48). They have had many reported problems so he said. He said that I would have to replace the filter with another (fiberglass) before they could install.

Has anyone had experience with installing SWG's with Nautilus filters? Do they corrode and fail readily with salt water? It's stainless steel so I don't see how they would corrode. If they do fail does anyone know how long it takes on average? Are we talking a few months and it fails or a few years?

 

[JasonLion]

The answer is mostly that it varies. It depends on the particular grade of stainless steel used in the filter, the salt level, the chlorine level, the condition of the filter, the water temperature, etc In some rare cases the filter can fail in months, years is more likely. Some of them last as long as they would without salt.

The installer don't want to be liable if your filter is one of the ones that fails, so his company won't let him do it.

 

[mac4lyfe]

Thanks Jasonlion... It's a Pentair Nautilus NS-48 stainless steel filter. Now I spoke to the folks at Pentair and they are going to have their tech folks call me back on corrosion. It seems strange that 3000ppm salt would corrode stainless steel. I'm now considering taking the SWG back.

 

[stevenbrla]

I can't answer your question, but one thing that everyone needs to realize is that the term "stainless steel" composes a very large group of alloys. I don't even know if that term has a real definition.

There are probably 100 or more SS "recipes". Some of the most common are 316SS, 410SS, 316L-SS, etc, etc. Unless a previous issue has arisien, you can bet the manufacturer has used the one that his particular vendor could source and work with with the mose ease (least cost.) Only when an issue arises do people (manufacturers) start questoning exactly what they're buying and what might work better in a given application. Then some much smarter metalurgist has to get involved and give a recommendation (or at least someone with a stronger opinion who might seem credible.)

All that said just to make the point that just because it says stainless steel, does not neccesarily mean that its equal to something else called stainless steel.... and there isn't a "best" s.s...... they all have their advantages/disadvantages... just like everything else in life.

Some is softer, some is harder, some is more corrosive resistant, while others are more resistant to errosion, and all have different cost variables.

Yes, I know this from too much experience (not in the pool industry.)

Enough already, huh?

 

[dschlic1]

I don't know about other types of stainless steels, but the 300 series (316, 304 etc) depend on surface passivation. This means that in a oxygen depleted environment, they will "corrode" quite rapidly. One example of this is being submerged continuously. One of the reasons offshore drilling platforms do not use stainless steel on their support legs, they use Monel.

 

[subslug]

You might notice some corrosion but I have a pool with 2 Nautilus FNS SS DE filters with SWGs and it's been working fine for 3 years now.
Our systems run 24/7/365 and I haven't seen anything more than a few surface areas of corrosion and those are generally from a slight o-ring leak during backwash or else an air bleed port leak from time to time.

From the inside of these tanks with the lids off they actually appear fine to me.
You'd have to think Pentair is aware of SWG by now, surely they aren't selling equipment not designed to handle the most popular chlorinating method going.

 

[JasonLion]

You'd have to think Pentair is aware of SWG by now, surely they aren't selling equipment not designed to handle the most popular chlorinating method going.

Absolutely, the new filters are all fine. But older filters, from before SWGs were popular, used varying grades of stainless steel. Some of the older ones fail when a SWG is added.

 

[woollybully]

I've got an older stainless filter (25+ years) and just installed a SWG. Do I just watch for corrosion (rust) starting when I do a filter tear down? I've been in the house about 8 years and there's always been some very slight corrosion on the welds of the filter.

 

[mac4lyfe]

Well I had already put salt in the pool (anticipating the install) so I'm too far in to turn back now. I'll just have to keep a good eye on corrosion.

I went ahead and installed the system myself since they wouldn't and it's been up and running since 10pm last night. So far everything is looking good.

My FC started at 3.5 ppm at 9pm last night (prior to install)
1:30am FC - 4.5 ppm
7:00am FC - 5.5 ppm
5:30pm FC - 5.5 ppm

I'm going to have to keep testing to figure my optimum rate. I'm currently on 50% output with a Hayward Swimpure plus.

 

[mac4lyfe]

You might notice some corrosion but I have a pool with 2 Nautilus FNS SS DE filters with SWGs and it's been working fine for 3 years now.
Our systems run 24/7/365 and I haven't seen anything more than a few surface areas of corrosion and those are generally from a slight o-ring leak during backwash or else an air bleed port leak from time to time.

From the inside of these tanks with the lids off they actually appear fine to me.
You'd have to think Pentair is aware of SWG by now, surely they aren't selling equipment not designed to handle the most popular chlorinating method going.

Well I feel a little better hearing that you have 2 with no problems. I'm not sure what Pentair is stance is. I tried calling them and I'm still waiting to hear from their tech people.

 

[chem geek]

I've got an older stainless filter (25+ years) and just installed a SWG. Do I just watch for corrosion (rust) starting when I do a filter tear down? I've been in the house about 8 years and there's always been some very slight corrosion on the welds of the filter.

There are two kinds of corrosion you might see. One is what you described at welds which is really galvanic corrosion between dissimilar metals. That is standard corrosion that can be alleviated to some degree by electrically connecting a sacrificial anode (which can be zinc unless you have any aluminum attached to the bonding wire in which case you need to use magnesium) to your tank and burying it into moist soil (i.e. ground it).

The other kind of corrosion is specific to stainless steel and with tanks usually results as deep pitting corrosion so won't be easily visible (i.e. there won't be any sort of "rust") until it breaks through at which point you have a visible leak. It's more like a pin-prick or depth crack through the metal. This kind of pitting corrosion occurs not due to the higher conductivity of the salt water, but due to its higher chloride content that inhibits the formation of the passivity layer that protects the underlying steel from corrosion. The sacrificial anode described above might help in this situation as well.

I suspect that even if corrosion is accelerated with the saltier water, the fact that your tank has lasted 25+ years may indicate that it's more robust to begin with. Even non-SWG pools are salty -- just not as much.

Richard

 

[SeanH]

The other kind of corrosion is specific to stainless steel and with tanks usually results as deep pitting corrosion so won't be easily visible (i.e. there won't be any sort of "rust") until it breaks through at which point you have a visible leak. It's more like a pin-prick or depth crack through the metal. This kind of pitting corrosion occurs not due to the higher conductivity of the salt water, but due to its higher chloride content that inhibits the formation of the passivity layer that protects the underlying steel from corrosion. The sacrificial anode described above might help in this situation as well.

I suspect that even if corrosion is accelerated with the saltier water, the fact that your tank has lasted 25+ years may indicate that it's more robust to begin with. Even non-SWG pools are salty -- just not as much.

Richard

I replaced a Nautilus SS DE filter later year for exactly that...a pin prick size hole that leaked. I don't have a SWG.

Sean

 

[mac4lyfe]

Dang, just when I was feeling better Well I guess I'll be checking the system for leaks several times daily.

 

[subslug]

Dang, just when I was feeling better Well I guess I'll be checking the system for leaks several times daily.

:lol:

Relax, if it does happen it's liable to be years down the road. Honestly, like chem geek says you've always had salt in your pool to some degree. I'm always amazed at how little salt we even need in our pools to generate chlorine. It seems so minimal to me.
Plus, if you do get a pin hole the salt build up it leaks out is liable to seal it up for you. :lol:

 

[mac4lyfe]

Hehe... Ye my pool must have had a high level of salt already. I like an idiot didn't measure my salt level before adding salt. Luckily I only added half of the 18 bags of 40lb salt before testing. After only 9 bags I was up to 3400ppm which is ok for my unit. It would have been a big mess if I would have used all 18 bags. I'd probably still be draining as we speak

 

[mac4lyfe]

Update: I'm still using the Nautilus filter but it has developed a couple of pin size holes. I was able to patch them with an epoxy paste but I'm about to replace the filter in the next few weeks because I'm sure more leaks are about to come. BTW: I did not ground it or use a sacrificial anode so I'm not sure if that would have saved it.