Sacrificial Anodes with Deposits at Coolers 2

[Reformator]

Dear all,

During this turnaround we discovered that some coolers had deposits at sacrificial anodes at distribution chamber and some were consumed. Those anodes that had deposits on them didn't have any traces of deposit at the tube bundle. If anybody had an experience on having the same issue could you please advice why it is happening?

 

[MJCronin]

Again, we have zero background information and are expected to perform miracles ...

Seawater service ?... Brackish water ? ... Something else ?

Velocity and operating temperatures ?

Zinc anodes of some type and weight or something else ?

Drawings, areas protected ...other information ?

Dead sea salinity or Baltic ???

Always take a single picture from about 10 meters away .... no sense in wasting your time with close-up pictures ...

MJCronin
Sr. Process Engineer

 

[LittleInch]

That looks to me like someone has thought "Lets stick an anode on this as it prevents corrosion"

Oh wait - It doesn't actually work on a flowing water system inside a pipe.

Note that only the immediate area around the anodes is relatively corrosion free.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Reformator]

Analyzes of treated water from the lake

Total Hardness mg/l CaCO3 max. 1100
Calcium Hardness mg/l CaCO3 max. 550
Organic substances mg/l max 50
Total Iron mg/l max. 2.5
Cooper micro g/l Cu max. 200
Suspensions mg/l max. 50
Sulphates mg/l SO4 max. 650
Silica mg/l SiO2 max. 25
Clorides mg/l Cl max. 350
Sulphur mg/l S to be noted
Conductivity S/cm Max 2500
Orto Phosphat mg/l PO4 2-6
Total Phosphate mg/l PO4 3-8
Total Zinc mg/l Zn 0.25-0.75
pH 7.8-8.3
Alcalinity m mg/l CaCO3 max 200


Generally, operating temperature of water between 18 C(inlet) - 40 C (outlet)
Sacrificial Anode - high purity Zn

I am curious if anyone from here have encountered deposits at sacrificial anodes

 

[TugboatEng]

Can you clarify what deposit at sacrificial anode means? Your image shows a low to moderate amount of corrosion and a normal looking anode.

 

[Reformator]

One question arises more questions

At the picture you can see white powder like substance at sacrificial anode at distribution chamber. From my experience I cannot say that it is low to moderate corrosion and it doesnt actually looks good to me.

 

[EdStainless]

Who did the anode design? With that placement the only thing that could be protected is the plate that it is mounted to and maybe the surface across from it.
If the temp, pH and corrosion potentials are wrong then the anode won't be dissolving much if at all and then minerals and biological films can form.
Straight Zn? why such a high potential?
What is the CI for this water?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[MJCronin]

Was there an electrical check made between the Zinc anode and the carbon steel that was to be protected ?

Based on my evaluation of this single picture (taken at a distance), it looks like the zinc provides zero protection

How is the zinc attached to the structure ? ..... Are there and sketches/drawings that show the attachment method/details ?

Zinc anodes are commonly bolted to the structure to be protected in marine applications .... Whatever you do, DO NOT PROVIDE ANY CLOSE UP PICTURES !!!

A more typical zinc anode has white deposits and the adjacent CS areas have a light oxide coating (No large blisters like you have)

MJCronin
Sr. Process Engineer

 

[LittleInch]

Reformator,

Those anodes are basically useless and you should just rip them off and coat the inner pipe surfaces in something which can actually prevent corrosion.

I don't know enough about water chemistry but they look like calcium deposits to me or maybe a few snails which have got encrusted.

what is this thing anyway?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SJones]

@LI
It is feasible to provide sacrificial anode CP to such areas, but it requires competent design and supervision of installation. EN 12499 has a small section on the subject, but not overly definitive. The designer should have been certificated ISO 15257 Level 4 minimum with sectoral qualification for inner surfaces of metallic structures.

The OP picture appears to be more an issue of biofouling control than CP.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[LittleInch]

Steve,

I was waiting for someone who understands the black arts of CP to join in, but sacrificial anode protection of a steel inlet water pipe is a new one to me.

Given the large are of what appears to be bare metal, I'm far from surprised some anodes have vanished.

I still think the area that you can protect using such internal pipe anodes must be very small and I can't really see how the current path works in a moving fluid?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SJones]

The rule of thumb would be around a length of 2 to 5 pipe diameters as a protection zone with a decently designed and installed system. The conducting electrolyte doesn't have to be stationary - think of ships.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[bimr]

The poster submitted a picture of something that looks like a flow straightener or personnel entry barrier. The application wasn't mentioned so there is little to go on. Zero background information and one is expected to perform miracles.

Based on the water appearing to be brackish, it may be that the sacrificial anodes in static water had deposits from the brackish water and the sacrificial anodes in flowing water may be eroding away.

 

[LittleInch]

Steve,

Thanks for the ROT - I knew there was a good reason no one does this for trying to protect the inside of pipes.

I hadn't really got my head around how the ships thing worked - thought it might have been more for when they are moored up, plus you hope the hull is actually painted at least. The picture of the pipes indicates no internal coating at all.

But as usual we have <5% of the detail, so....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MJCronin]

Like most of the postings from the Third World, the OP has abandoned this thread ...



MJCronin
Sr. Process Engineer