Plate & Frame Heat Exchanger - leaks (pin holes)

[cokecp]

Anyone ever experienced pin holes in the exact same location on different plates in a plate & frame heat exhanger? The supplier tried to tell us it was due to a chemical used in our process, but the holes were in the same spot on multiple plates - 141 out of 258 stainless steel plates.
This clearly looks like a mfg defect with the stamping to us???

 

[EdStainless]

What alloy? and What service? What chemical is it that they are taking issue with?
I may be that your service is aggressive enough to attack in crevices and that their design places the tightest crevices in the same place on each plate.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[cokecp]

Thanks for your response. Material = 316SS. Media used for cooling is food grade polypropylene glyclol. Chill from ambient to ~35 deg F. Chemicals used for cleaning are caustic (25%) and paracetic acid (not used at the same time).

 

[IRstuff]

Any corrosion inhibitors in the PG? How long before the leaks developed?

TTFN

FAQ731-376

 

[stanweld]

Have you analysed the flow in the locations corroding (stagnant zones)? Is the corrosion ocurring along welds or at near crevices.

 

[rmw]

Can you give us a description of where on the plate that this pin-holing is occurring? Is it occurring near a contact point (the point on the plate where it contacts an adjoining plate for structural stability) or away from contact (non supported) areas? Is it occurring near the ports? Top half/quarter of the plate, bottom, in the gasket trays, etc.

Give a basic description of the HX, two pass, four pass, more than that pass, simplex, duplex (two services in one frame) type? If it is mechanical and not corrosion, we need to know a lot more about the physical characteristics of the plate. What is the size of the heater, length and width of the plates.

Is there any significant temperature cycling?

Did you get any spare plates (or have any plates from the original plate pack that were pulled out for performance reasons) that you can look at to examine the area in question prior to being in service?

Sorry, but for me if it were chemical attack the chemical wouldn't be selective enough to pick this special point on each plate and ignore all the other crevices and corners and bends and twists and turns and even dead zones like gasket trays unless you had a phase change at the offending point. Right now I am going with mechanical defect or thinning due to rubbing at contact points. But then again, the jury hasn't come back in yet either until we hear from you more about his heater.

rmw

 

[Zoobie]

cokecp:

I have seen pinhole leaks in a plate and frame exchanger occur in the same location. In this case 'same location' meant within the same localized area on different plates. I don't know if that is what you mean by exact same location. This was definitely process related. I also have seen multiple gasket failures through a pack at what I would say is the "exact same location" and again this was definitely process related.

However, if you are dealing with the pinhole occuring quite precisely at the exact same location I would side with rmw.

 

[cokecp]

Sorry for the delayed response - I was waiting on the plates to be analyzed. I have attached photos of the failures. There are multiple plates with failures in the SAME location (not close proximity, but SAME location).
The mfg is saying it is corrosion but as rmw says I can't see how it would be so selective as to fail multiple plates in the same location. Here is some data on the plates:
Material = 316SS (not 316L)
Thickness = .6mm
Plate size - 18" wide x 36" tall
Gasket Material = EPDM
Total Plates = 260 (at least 140 had pin-holes)
Using 30% PG (I am told with a corrosion inhibitor)
This is a 2-pass chiller
The exhanger is used for chilling rather than heating. The unit does see 185DEG F for approximately 20 minutes once per week.

http://files.engineering.com/getfil...f78-480e-9c8a-dd16d704521c&file=Corrosion.jpg

http://files.engineering.com/getfile.aspx?folder=eb45f6b8-f8e5-405b-bf99-bb2ddbdba55e&file=Crack.jpg

http://files.engineering.com/getfil...3-4b73-ab38-2bd1286600c4&file=Deformation.jpg

 

[rmw]

When you say "have the plates analyzed" what was the analysis, who did it and what was the result?

I'm not a metallurgist and there are some really good ones that lurk this site, but if this was my plate I'd be sending it out to some metallurgical lab to see if it is what it is said to be.

I would expect chemical attack of the plate to be as EdStainless' signature used to say 'relentless' and to exhibit itself much more wide spread than these locations.

One of the pictures looked more like cavitation than corrosion. I am trying to get my mind around how that could happen at that particular location.

rmw

 

[IRstuff]

Is there some sort of plating on the 316SS?

There does appear to be some sort of consistent mechanical damage. However, you need to look at as-delivered plates versus your failed ones. Are there damage indications on new plates?

Who assembles the plates into the exchanger, you or the supplier? If you, then you need to dismantle a new assembly and see if there's some sort of precursor damage or other feature that you can correlate to the corrosion.

TTFN

FAQ731-376

 

[EdStainless]

Is there any chance for there to be air entrained in your flow? I wonder about surging or pulsing from gas slugging.
Is the damage at points of contact between plates or at gaskets?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[12gauge]

Another thing to note is that 316ss is often passivated in acetic or nitric acid as a final part of the manufacturing process. perhaps the HEX company could look into their passivation process (if they have one) and look for something that could have contributed to your problem.

 

[rustbuster]

You may have a Cl- SCC problem. Had a similar experience with multiple plate failures. Turned out it was from chlorides / Bromides leaching out of the gasket material and or glue.

Check the gaskets and thier curing compounds as well as the type of glue used by the manufacturer.

Good Luck

 

[rmw]

If it was a Cl - SCC problem, why did it pick this consistent location on a lot of plates and not appear randomly on the plates?

I think EdStainless's question bears further investigation. If there is a phase change within the exchanger at a certain point of differential pressure it could explain the area around the pin holes in the first photo.

rmw