The importance of material selection cannot be stressed enough.

With the equipment comes the material of the equipment, and every material is prone to corrosion in some way.
For most fields such as defence, oil and gas, automotive, and marine, the qualification tests for the material selection begin and stop with the mechanical properties and composition.
There is not even a mention of the possible corrosion phenomena for that particular material.
This results in ‘surprises’ when there is a serious failure. Only after that are the corrosion investigations carried out and modifications done.
However, by that time, it may be too late for some.
Hence, it is necessary that the concerned personnel in the industries do not cut costs where corrosion is known to be an issue.

What is Corrosion Planning?

It is critical to begin a “CORROSION PLANNING” to ensure that the corrosion risks of every material that is qualified, and every component that is bought are noted BEFOREHAND.

The possible areas of corrosion, environment of exposure, critical mechanisms, past studies, and required non-destructive corrosion testing should be identified. There are terms such as critical reliability variable (CRV) and integrity operating window (IOW), as given in API 584 and 970.
There must be a step where the corrosion risks are listed out for each component, no matter how small. The risks include not just the individual corrosion properties, but also the interaction between the various components.
The possible crevice locations should be mentioned in the print. The issues that may result during exposure to operating medium should be listed.
The types of corrosion seen previously should be mentioned and the risks must be labelled from high to low in the entire component.
A simple example is the corrosion planning for a lead acid battery and aboveground storage tanks.

Further requirements of the planning

Just the plain label of ‘This material has a high corrosion resistance’ is not enough. 

What does it mean? What are its corrosion potential and corrosion current density in the operating medium? What is its mpy in that operating medium?
It is essential to integrate the research aspects with the industrial requirements to arrive at the complete picture, as discussed in this free webinar.
If such aspects are included in the initial stages of material selection and product planning, the industries will be ready for any untoward incident that may happen. 
In most cases, they may even be prevented.
An example of this is API 970 which talks about a corrosion control document for every facility. This includes concepts such as corrosion loops.

Would you like to test your corrosion knowledge now?

Click here for the list of quizzes!

😀Happy learning!😀

Resources for a corrosion beginner

Corrosion is a complex subject. It is difficult to pick and choose the starting point. It is very easy to spiral into a confused state of mind if the right resources are not available.

Hence, I write this blog post to list out a few books which are great if you are a corrosion enthusiast.
Here goes –
1. Corrosion Engineering by Mars. G Fontana
        I love this book and I always refer to it for my work.

2. Peabody’s control of pipeline corrosion – 

3. Corrosion engineering – Principles and practice – Pierre Roberge

The website has a more extensive list of corrosion articles.

Other than that, there are online corrosion magazines which you can access –

1. Materials performance –


3. CORROSION journal –  it has a few open access articles.
Check out these resources as a starting point!

Corrosion rate and pipe design

Corrosion is a serious issue. However, corrosion engineers are rarely asked about it during the designing of components. It is only when the components fail that people remember there are people who have studied corrosion for their whole life and would provide a solution. The design problems are really quite simple, and the loss of money could have been avoided had the company bothered to involve a corrosion engineer in the first place.
Let me illustrate this with an example of a factory near the sea.
Suppose a mild steel pipe is fitted inside the factory to transport 1 wt. % hydrochloric acid. The engineer has a choice between selecting pipes of 5 mm and 10 mm thickness. To save money, they go for the pipe with the 5 mm thickness because it has been ‘successfully used by the other customers’. Over the course of a year, it is seen that the pipe has started leaking at certain places. Further investigation reveals that those sections have thinned to half of their thickness.
Now, a coupon test is carried out to assess the corrosion behaviour. The corrosion rate is calculated to be 2.5 mmpy, which means the alloy was prone to corrode and lose 2.5 mm of its thickness in one year. Hence, the corrosion rate in the design of this pipe should have been crucial in the beginning itself, because now the company has to bear the cost of not just the original pipe, but also the new pipe with greater thickness.
So, the company decides to go for a 10 mm thick pipe for the transportation in the enclosure.
It further decides that it will construct a piping system that enables the loading of the acid from outside the enclosure. Hence, it extends the pipe to the outside of the factory.
Sure enough, they are back to square one within a year, wondering what went wrong with the pipe outside the factory.
The answer was in the extra plans that they made. The recommendation of 10 mm diameter pipe was made for the pipe in the internal environment. The problem was in the extension of the pipe to the exterior.
The exterior of the pipe was exposed to the moisture and ions in the air. The corrosion rate of the steel in air is 2.5 mmpy. So now the pipe was undergoing an internal as well as an external corrosion. As a result, the total corrosion it was experiencing was once again 5 mmpy.
This led to the corrosion of the pipe on the exterior.

The drain mystery

I recently moved to a new house. As expected, there was a lot of cleaning up to do. One of the tasks was the cleaning of the washbasin. Usually, the drain is a circular part with  5 to 6 holes for the water to flow out. What I saw was this –

I have not had a chance to analyse the material of the drain. However, a quick search tells me that this is most probably stainless steel. The water that this drain is exposed to is the bore water. Thus, the drain has encountered a lot of chlorides. There is general as well as localized corrosion.

The damage started off as a simple process of pitting. Pitting due to chlorides is one of the most common headaches for poor stainless steel. They break the passive oxide film, and reach the underlying fresh iron. This iron then reacts with the usual suspects (ions, oxygen, water) and forms what we see as the rust.

As can be seen in the picture, the thin sections of the drain between the holes have disappeared in three places. This may have happened because the pits formed continued to grow through the thickness of the material, which finally gave way and fell down the drain. The shape of the circle to the top left is distorted and we can observe a small nick in the circle. There is also a variation in the widths of each of the sections between the circles – all because of corrosion.

Then, there is the green color. This is the corrosion product ferric chloride. A quick look shows the green formation around the part between two holes at the top right. General corrosion is visible, and there may be pitting going on underneath the corrosion products.

We will have to wait and see if that small section is the next to break off.

UPDATE: It did break off.

Corrosion – the bane of all the industries

Corrosion is the journey of an element from its most active form to its most stable form. 

The birth

At the place of its birth, inside the earth, an element such as iron comes into contact with atmospheric oxygen, chlorides, sulphate, and moisture. and is quite happy to remain in peace with them in the form of Fe2O3, Fe3O4, FeCl3 and such.

The growth

It is then extracted and made to go through a number of processes which separate it from the ions and bring it to its elemental form. It is then put into use to make steel, where it coexists with carbon, manganese, chromium, and other alloying elements.

The interaction

However, iron has three electrons that it desperately need to give away. That is exactly what it does the moment the steel is brought out from the factory and put outside in the shed. Iron is more than happy to reunite with its old buddies – oxygen and moisture. It gladly gives away its electrons to them and returns to its peaceful state of Fe2Oand Fe3O4.

And that is how the corrosion of steel begins.

😀Happy learning!😀