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corrosion

Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, carbonate or sulfide. It is the gradual destruction of materials (usually a metal) by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfates. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal and results in a distinctive orange colouration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term "degradation" is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases.
Many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and chromate conversion, can increase a material's corrosion resistance. However, some corrosion mechanisms are less visible and less predictable.
The chemistry of corrosion is complex; it can be considered an electrochemical phenomenon. During corrosion at a particular spot on the surface of an object made of iron, oxidation takes place and that spot behaves as an anode. The electrons released at this anodic spot move through the metal and go to another spot on the metal and reduce oxygen at that spot in presence of H+ (which is believed to be available from H2CO3 formed due to dissolution of carbon dioxide from air into water in moist air condition of atmosphere. Hydrogen ion in water may also be available due to dissolution of other acidic oxides from the atmosphere). This spot behaves as a cathode.

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  1. T

    Corrosion on Pipe / Fittings

    Hi, I am probably being unduly paranoid here but I noticed under our kitchen sink that there is some corrosion evident on a small section of copper pipe between compression fittings on the hot water feed. There are take offs for an outside hot and cold tap together with isolation valves and...
  2. C

    Underfloor copper pipes: corrosion and pin holes

    Bungalow built in 2001. All copper pipework (water and heating) runs in channels of expanded foam polystyrene between a concrete floor and OSB boards. Pipe are lagged in stitched felt and what looks like bubble wrap with sand (?) over the top. During the bathroom refit, I lifted up some of the...
  3. S

    Why has The handle on my hot tap been ‘eaten away’

    The handle on my hot tap has been eaten away. The same thing happened 2 years ago to the same tap. It looks like galvanic corrosion has anyone seen this before. The tap is definitely brass. The top is chrome plated.
  4. P

    AUS Steel galvanised pipes and lead

    Hi there I’m 10 weeks pregnant and found out we have some steel galvanised pipes with corrosion which was causing our tap water to run discoloured for a few seconds when not used for a couple of days. I understand this is from rust but was told lead could also be leaking into our water because...
  5. M

    Power flush & system corrosion

    In December 2022 (i.e. 5 months ago) I had a full system power flush conducted. Now the previously clear UFH flow gauges are black again. Is it possible that enough internal corrosion could have occurred in this time period? I had a separate plumber out a month ago to test some pipework and he...
  6. N

    Basin bottle trap corrosion

    The Basin bottle trap is in bad condition and begin to loose water due to corrosion (I believe it is lead). May I use pattex putty paste or collak as an emergency solution? How can I loosen the bottle trap nuts? They are so rusty and calcified I am afraid they may break if try to unscrew them...
  7. Hayleymariewood

    Corrosion on top of boiler

    Hi, I have a Vaillant boiler 9 years old and the top is showing some corrosion from an outside pipe leaking on top I think. Is this an expensive thing or is it easily fixed? Or do you think I will need new boiler? Thank you so much for reading!
  8. R

    Corrosion on pipe connections.

    Chaps, I'm in Tenerife looking after a few houses. They are only 3-4 years old and this is the second solar tank to fail due to severe corrosion on the collector connection. Has anyone got any ideas why this should happen and both failed on this one connection after such a short time whereas...
  9. B

    Adding corrosion inhibitor

    Hi all, DIYer after some advice. I’ve drained my CH system (combi boiler) to replace a couple of radiators. The new rads have been fitted and I’ve been trying to add inhibitor to the system. I’ve isolated both valves on the radiator, opened the vent and removed the plug. I have a flexible funnel...
  10. S

    Corrosion problem in central heating system with standard plastic piping?

    Five years ago I had a new central heating system installed. The pipework for two of the radiators was done in plastic, running under the floorboards. Although the system was dosed with plenty of Sentinel X100 inhibitor, after about 18 months the water suddenly started to go brown, and I had to...
  11. T

    Best way to get rid off corrosion in CWST on my copper fortic cylinder?

    Hi all just a quick one what would be the best way to get rid off corrosion in my CWST on my copper fortic cylinder?
  12. A

    excessive sludge and corrosion

    I have a vaillant boiler eco plus that came with a 5 year warranty. On the last service no issues were found ( although the chamber wasn't physically opened - not required by the manufacturer as it would then require new seals) A water sample testing came positive and was advised to have the...
  13. siricosm

    How to reduce corrosion in vented heating systems

    Some vented heating systems seem to sludge up, and yet other remain remain remarkably clean after many years service. Why? Corrosion is caused by oxygen. Eliminating leaks and inhibitor helps, but the F&E tank is open to the air, so oxygen can freely get in there. Is it possible to design a...
  14. Sc0tty

    New Build Heating System Worries

    Hi PlumbersForums. I've been having some issues with my central heating system in a 4 year old new build property for over a year now. I have some mental health issues with anxiety so this might be exaggerating the problem somewhat but please bear with me. My issues start with Plumber A doing...
  15. A

    Vaillant ecomax flue corrosion?

    Hi guys, looking at a vaillant and the flue shows signs of corrosion on the air intake, I put my analyser in and o2 was coming back at 20.9% with no co readings so flue integrity is fine. It must be caused by water ingress from rain but wondering if I should at risk it or not.
  16. D

    Unusual Copper Pipe Corrosion

    Hi, I had some of the floorboards up today and I spotted a short section of copper pipe for the heating that is extremely corroded. The copper is flaking away in layers and looks like it should have burst long ago. Not the usual green residue. Does anyone know what may have caused the...
  17. P

    Can I re-use corrosion inhibitor?

    I'm going to attempt some work on my central heating system which will involve partially draining it down, possibly a number of times. I have a small water pump, so in theory I could keep the drained water and pump it back into my system. Then I wouldn't have to worry about replacing the...
  18. SlimD

    Copper pipe corrosion

    Got called to a leaking stopcock recently. Fine jet of water spraying out from compression joint. On closer examination I found the copper had corroded under the olive. Please see photos. Anyone seen this before? Is this pinhole corrosion?
  19. P

    Copper water cylinder needs replacing??

    Our indirect copper water cyclinder has started leaking. Not a flood but enough to wet the whole floor in the airing cupboard. Could not find any obvious leaks from pipe joints, shower pump etc. so called in a plumber. He cut away insulation layer at bottom and found heavy corrosion. He has...
  20. C

    Leaks and corrosion in old kitchen mixer tap - what's required?

    I'm new here - please be gentle with me! Our kitchen tap is leaking, both from the cold tap, and the ‘bottom’ of the mixer spout. Pictures attached. Can anyone tell me what should be present on the mixer spout – i.e. should it be a washer or an O ring? The PTFE tape is only just holding...
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