The above photo is that of an underground pipe carrying a fluid high in chloride concentration.
As can be seen in the photo — there is a big rupture of the pipeline leading to a unwarranted and unplanned plant outage.
What can engineers do about it? The usual way of thinking about is to quickly find a way to monitor the development of such failures in time so as to attend to the problem as quickly as possible with ruthless efficiency.
However, to monitor development of pitting / crevice corrosion – (the failure mode in this case) – is neither easy nor available. And even if there were a technique; its benefit, as in all cases of condition based maintenance of condition monitoring, is at best fundamentally limited in its effectiveness. Why? Simply because it doesn’t help improve the MTBF (Mean Time Between Failures). Without substantial improvement in MTBF, we can hardly expect to improve performance, productivity and profitability through maintenance of plant assets.
Such an approach to maintenance is more in keeping with the present requirements and needs of the industries. Maintenance is not about maintaining and restoring assets to its original condition. In present context, maintenance is directly linked to an organization’s profitability and survival under all economic conditions, at the minimum possible cost.
With this in mind, I invented the IAR (Initiator, Accelerator, Retarder) technique.
It means that for every failure or failure pattern or behavior pattern there would be at least one element in the system that would initiate or start the failure process. Similarly, there would be atleast one element in the system that would accelerate the process. Likewise, there would be atleast one element that would help retard the failure process.
Once these I, A, R elements are identified, the job of prolonging the life of a system at the least cost becomes relatively easy and more effective, which can be stated as follows:
1. Eliminate/Avoid the Initiator (s)
2. Prevent the Accelerator (s) from acting
3. Strengthen the Retarder (s)
The next step is to monitor the presence or development of the I, A , R s — if found contextually appropriate and effective.
Coming back to our case, the IAR s are the following:
Initiator — Material
Accelerator — Lack of cathodic protection
Retarder — Steady process that would prevent sudden increase in chloride concentration.
Therefore the set of solution would be:
Eliminate Initiator — Select material having high PREN (Pitting Resistance Evaluation Number)
Prevent Accelerator — install cathodic protection.
Strengthen Retarder — closely monitor the process to prevent sharp fluctuation of chloride concentration.
The above measures would not only help in preventing pitting/crevice corrosion but also prolong the life of the pipeline — helping the plant to become more productive and remain so for a longer time.
Moreover, it proves to be an effective maintenance planning tool than existing approaches.