Rust inside my Jandy DE Filter

[wakerider017]

Well I just did an ascorbic acid treatment on my pool and couldn't believe how clean it made. I didn't realize I had that level of staining. I noticed some slight yellowing the the pebble sheen, but didn't think it was really that bad. What made me do it in the first place was the yellowing on the plastic drains and jets...

Now on to the reason I am actually posting this thread. I've noticed some rusting going on in my Jandy DE filter. It has been there awhile (4.5 yr old pool now) and has progressively gotten worse. I took some ascorbic acid mixed water to it and it really didn't do much.. Then I tried muriatic acid and it took it right off. Looks super clean now, but I have a feeling it is just going to rust again.

Any idea why this metal band is rusting? Anyone else with a similar experience?

 

[HermanTX]

I have a Pentair DE which has a similar metal band. It is not made of full stainless plus it has a weldment on it so expect some corrosion over time. I clean my DE filter annually and I just wipe it down.

 

[JamesW]

It is very common.

Most likely, the steel is damaged as it is heated and formed into the round shape.

Processing can damage the molecular structure.

Getting the proper shape is difficult without damaging the steel.

 

[1poolman1]

Well I just did an ascorbic acid treatment on my pool and couldn't believe how clean it made. I didn't realize I had that level of staining. I noticed some slight yellowing the the pebble sheen, but didn't think it was really that bad. What made me do it in the first place was the yellowing on the plastic drains and jets...

Now on to the reason I am actually posting this thread. I've noticed some rusting going on in my Jandy DE filter. It has been there awhile (4.5 yr old pool now) and has progressively gotten worse. I took some ascorbic acid mixed water to it and it really didn't do much.. Then I tried muriatic acid and it took it right off. Looks super clean now, but I have a feeling it is just going to rust again.

Any idea why this metal band is rusting? Anyone else with a similar experience?

Yes, it is going to rust again. It is not a problem and very normal for all brands of pool filters that have "not so" stainless steel in them. If it concerns you, be sure to keep a sequestering product in the water. Something like GLB "Sequa-Sol" or Natural Chemistry "Metal Free."

What is Sequestering Agent and Why do I need it?

I was looking at my plaster's (Premix Marbletite) chemistry recommendations and here is what they recommend POOL WATER CHEMISTRY WARRANTY CLAIM PROCEDURES It is necessary for the longevity of your pool finish and as a condition of this warranty, that the following chemical guidelines and...

www.troublefreepool.com

 

[JamesW]

High temperatures

A less common form of rusting occurs after the stainless steel has been exposed to very high temperatures in the 750–1550°F range. This type of corrosion is found in welding applications in which stainless steel is heated and then cooled. Sensitization can occur, where the carbon and the chromium bond to form carbides. This causes the grain boundaries to become chromium deficient, and the chromium oxide layer becomes discontinuous. Heat sensitization runs the risk of ruining stainless steel forever.

Stainless Steel Cleaning and Maintenance

Protect stainless steel from rust using proven cleaning methods and passivating treatments.

www.reliance-foundry.com

Chromium carbide is also formed by intergranular corrosion, which occurs when some types of stainless steel are heated to the point where the chromium can bond with carbon atoms. This reduces the amount of chromium and chromium oxide available, which prevents corrosion. This process is known as sensitization. However, when this happens to stabilized grades of stainless steel, it is referred to as a knifeline attack, and in these cases chromium carbide is typically undesirable because it is detrimental to the corrosion resistance of some stainless steels.

What is Chromium Carbide? - Definition from Corrosionpedia

This definition explains the meaning of Chromium Carbide and why it matters.

www.corrosionpedia.com

 

[JamesW]

Take a strong magnet and see if the magnet is attracted to the steel uniformly or if the attraction is different where the steel is rusted.

 

[JamesW]

Stainless contains a minimum of 10.5% chromium.

When oxygen combines with the chromium, it creates a chromium oxide surface layer.

The chromium oxide is known as a passive film which seals the iron in the alloy away from the air and water in the environment.

This film gives stainless its rust-resistance.

There are four main types of stainless steels: austenitic, ferritic, martensitic, and duplex.

Austenitic stainless steel is dominant in industry and comprises over 70% of total stainless steel production.

Its properties include a maximum of 0.15% carbon and a minimum of 16% chromium, yielding very strong protection against rust.

Ferritic stainless steel has reduced corrosion resistance compared to austenitic grades, but fares better than martensitic stainless steel.

Duplex stainless steels have high resistance to localized corrosion particularly pitting, crevice corrosion, and stress corrosion cracking.

Stainless steel rusting occurs when the passive layer is damaged and there is not enough chromium for it to reform.

To clean use a soft cloth to apply an oxalic acid solution or a product like e-nox

E-NOX CLEAN™ – Walter Surface Technologies

Heavy-duty stainless steel cleaner/brightener. Products

www.walter.com

https://documents.walter.com/webform/documents/walter/msds/usa/en/L-59.pdf

Passivation procedure

A stainless steel surface can be damaged through mechanical means, extreme heat or chemical damage.

When this happens, iron is exposed, and the material is once again subject to rusting.

The stainless steel part must be thoroughly cleaned.

Stainless steels cannot be passivated unless the surface is clean and free from contamination and scale.

Passivating treatment

The stainless steel part is immersed in a passivating acid bath.

Any one of three passivating approaches can be used: nitric acid passivation, nitric acid with sodium dichromate passivation, or citric acid passivation.

 

[JamesW]

Most Austenitic Stainless Steels are non-magnetic.

Certain types of stress or heat can damage the steel and make it magnetic and also make is susceptible to corrosion.

Most likely the selection of steel is not correct for the purpose or the machining with heat and stress is causing damage to the steel’s molecular structure.

They might need to change the grade of steel, the processing or maybe do a passivation treatment after the processing is completed.

 

[wakerider017]

Thanks guys. I just wasn't sure if this amount of rust could end up being a problem (source of stain) in a 20K gallon pool or if this is essentially a drop in the bucket and the real culprit for any staining I am seeing is fill water?

 

[DavidArmenB]

Thanks guys. I just wasn't sure if this amount of rust could end up being a problem (source of stain) in a 20K gallon pool or if this is essentially a drop in the bucket and the real culprit for any staining I am seeing is fill water?

As members stated above, this is very common and not just for Jandy. In fact i am sure this issue is more documented for Pentair filters!

Regarding the amount of rust, even though it may look a lot, that is not much rust at all. It removed a negligible amount of material from the steel and it would need much much much longer before it began having any effect on the structural integrity of the band.