Sacrificial Anode on isolated copper alloy pipe

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Discussion Overview

The discussion revolves around the use of a sacrificial anode in an isolated copper alloy pipe within a seawater cooling system. Participants explore the type of corrosion being mitigated by the anode and the conditions under which galvanic corrosion occurs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question the necessity of a sacrificial anode for an isolated copper alloy pipe, noting that galvanic corrosion requires electrochemically dissimilar metals in contact with each other and an electrolyte.
  • Others suggest that the sacrificial anode may protect against other types of corrosion, although they do not specify which types.
  • Participants inquire about the physical setup of the system, including the connections and fittings at the ends of the pipe, and whether there are nearby metal components that could influence corrosion.
  • One participant hypothesizes that the dissolution of copper into the seawater could occur, with the sacrificial zinc anode preventing this loss, leading to a higher concentration of zinc in the outflow.
  • Another participant raises the issue of the assumptions regarding isolation, suggesting that imperfect isolation could lead to unintended corrosion processes.
  • There is mention of electrolysis as a potential process driving the dissolution of metals in the seawater, although the specifics of this process are not fully explored.

Areas of Agreement / Disagreement

Participants express differing views on the role and necessity of the sacrificial anode, with no consensus reached on whether it is needed for galvanic corrosion or another type of corrosion. The discussion remains unresolved regarding the specific corrosion mechanisms at play.

Contextual Notes

Participants highlight the importance of understanding the physical connections and conditions of the system, including the potential effects of heating seawater and the materials used in fittings. There is uncertainty regarding the implications of isolation and the specific processes involved in corrosion.

Ters
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TL;DR
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?
 
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Ters said:
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?).
 
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?
 
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?
 
Baluncore said:
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.
 
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.
 
Baluncore said:
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?
 
Ters said:
What kind of process drives this dissolution?
Chemistry. Seawater is NOT saturated with copper.
 
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.
 
  • #10
the process may be called 'electrolysis',
which is driven by electrolytic exchange
-meaning it eats the most readily available metal afaik,
the electricity
 

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