Sacrificial Anode on isolated copper alloy pipe

[Ters]

TL;DR Summary

Isolated copper alloy pipe where seawater flows through protected with sacrificial Anode. What reason?

For a seawater cooling system there is a isolated copper alloy pipe where seawater flows through protected with sacrificial Anode.
For galvanic corrosion there needs to be two different metals connected in a presence of an electrolyte, since this isn't the case.
For what kind of corrosion is this anode protecting this pipe?

 

[Baluncore]

Welcome to PF.

TL;DR Summary: Isolated copper alloy pipe where seawater flows through protected with sacrificial Anode. What reason?

For galvanic corrosion there needs to be two different metals connected in a presence of an electrolyte, since this isn't the case.

What is not the case?
Seawater = electrolyte.
Copper alloy pipe is being protected by;
Sacrificial anode, (zinc?).

 

[Ters]

I don't see the reason why this pipe has to be protected, these sacrificial anodes (zinc) are commonly used to prevent galvanic corrosion, but the condition needed for this;

1. Electrochemically dissimilar metals must be present
2. These metals must be in electrical contact, and
3. The metals must be exposed to an electrolyte

are not present. So my question is is there any other way that there can be galvanic corrosion or is this to prevent another type of corrosion?

 

[Baluncore]

What is the sacrificial electrode attached to?
Is there a metal hull, or a propeller nearby?
Why does seawater flow through the pipe? Is there a pump?
What fittings are present at the ends of the copper alloy pipe?
Heating the seawater as it flows through the pipe may change the reactivity.
The two ends of the copper alloy pipe are attached to each other.
There should be a seacock at one or both ends of the pipe. What is the seacock made from?

 

[Ters]

What is the sacrificial electrode attached to?
Is there a metal hull, or a propeller nearby?
Why does seawater flow through the pipe? Is there a pump?
What fittings are present at the ends of the copper alloy pipe?
Heating the seawater as it flows through the pipe may change the reactivity.
The two ends of the copper alloy pipe are attached to each other.

The pipe is used in a seawater cooling system in an engine where the water is pumped, the pipe is connected on both ends with rubber connectors so it is isolated to other metals. The sacrificial zinc anode is placed within the pipe via a tapped hole where the zinc is on the end of a bolt.

 

[Baluncore]

When seawater runs through the copper pipe, I would expect to find more copper in the outflow than in the inflow water. The copper pipe would gradually dissolve in the seawater, but the sacrifice of the zinc will prevent that loss. The outflow will then contain more zinc, not copper.

 

[Ters]

When seawater runs through the copper pipe, I would expect to find more copper in the outflow than in the inflow water. The copper pipe would gradually dissolve in the seawater, but the sacrifice of the zinc will prevent that loss. The outflow will then contain more zinc, not copper.

What kind of process drives this dissolution?

 

[Baluncore]

What kind of process drives this dissolution?

Chemistry. Seawater is NOT saturated with copper.

 

[Dullard]

Learned the hard way:
'Isolated' can be a dangerous assumption. If Isolation is less than perfect... The 'Zincs' won't hurt anything if they aren't required.

 

[Uncanny3]

the process may be called 'electrolysis',
which is driven by electrolytic exchange
-meaning it eats the most readily available metal afaik,
the electricity