Martin: Bonjour monsieur Haris
Haris: Bonjour, Bonjour. Ça va?
Martin: Yeah, excellent, thank you. How are you?
Haris: Excellent, very nice, very good!
Martin: What are we talking about today?
Haris: It is not going to be us talking, it is going to be you talking.
Martin: Oh, excellent, I love that!
Haris: I know you love that, I know you love that. And you deserve that. So, today’s topic is a question coming from our friend Hamidreza Minaiepour, he wants to hear more about varnish. So, the question goes like this, as you can see on the screen: he wants to know about failure modes it causes, he wants to know about symptoms. Then, he wants to see the most appropriate way to detect this problem, especially at early stage. And, of course, as every good Reliability mind he wants to know what he can do proactively to avoid the problem.
Let me expand it on this, because you have 6 minutes to share all your wisdom, so that is more than enough, right?
Martin: Ha, ha, ha!
Haris: I like your smile, and I want to expand it with additional question; I hear this very often … and, is it a fact that some industries and some assets are particularly impacted by this problem?
Martin: Yes, that’s very good point, actually, because you do find that, to some extent, certain territories, certain industry types and certain machine types are more affected. But it’s because, when you look at the typical causes of the varnish that you see why this kind of happens to a degree. So, if we consider thermal decomposition and oxidation of the oil, and we know of course oxidation, it’s the WHAM effect. And I talk about WHAM effect in my training. WHAM, not the music group, but the WATER, the HEAT, the AIR, and the METALS. And, of course, the heat aspect and the thermal decomposition, that is going to be much more prevalent in territories where you’ve got higher ambient temperatures. So, in Middle east region, we have seen lot of this problem happening. But also, where you have got assets like gas turbines for example, where you have got extreme temperatures, such as the bearing housings, again, you see it more, in hydraulic systems, dependant on design of the system, you can get localised hot spots that might be causing some issues… But ultimately what it boils down to is the oil becoming stressed, or even better, think of it as the oil becoming distressed. Now, obviously, oil doesn’t have emotions, but I wish people did treat it as a living thing, but it does get distressed at times and there are number of factors that may drive that, and as I mentioned with WHAM – water, heat … AIR; AIR bubbles in the oil are problematic. Now you can remember, of course, when you had a bicycle pump, you put a finger over the end, and you squeeze the pump, how did your finger feel?
Haris: Hot
Martin: Yes, and just how hot do you think air bubble would be when you squeeze it at 200 bar pressure in a hydraulic system?
Haris: Up to 800 degrees centigrade?
Martin: Exactly! Ideal gas laws, if we use those, the adiabatic compression taking place, is up to 800 degrees centigrade. Now, that can lead to localised hot spots, but also, we term it micro-dieseling, because like a diesel engine the oil can auto-ignite at those temperatures. So, we have the stressing effect that’s causing issues. There is another factor that comes into play and that is the type of the base stock that we are using. Now, those that are familiar with American Petroleum Institute’s group rating for oils, for the base oils, you got your Group 1 – solvent refined, you got your Group 2 and Group 3 – hydrogen processed and hydrocracked, and then of course you’re getting into your Group 4 – Poly alpha olefin. Now, when you’re get into your Group 2, 3 and 4 you are seeing a much more pure base oil, there is a lot less impurity which leads to several problems; it affects the ability of oil to hold its oxidized molecules, often referred to as varnish holding ability, but it also impacts oil’s ability to dissipate energy. So, we do find that even static issues, antistatic issues can come into play. You may have heard users talking about, for example, burn marks on their filter elements, you may hear crackling sound from the filter element. That means that discharge is taking place. I’ve even seen a tank on oil rig where top of tank was bowed as a result of an explosion that took place in the tank. Which have been caused by electrostatic discharge. So that, in effect than, has an issue. So, base oil is one factor but then, of course, there are also additives.
Haris: So, is it correct what I hear very often that sometimes, some brands, are more affected than others? Or some oils seem to be more affected than others.
Martin: Yes, and it is true to say that apart from various regions and various machine types being more associated with a problem, even certain brands seem to be more of an issue. Which was really down to formulation, the PANA-type additives. I don’t want to sound clever here, because I am just reading it from a screen, but PANA-type; phenyl-alpha-naphthylamine, is actually one of the affected types. Now, most of that is now a level playing field in terms of a brands, so brands are not so much an issue any more really, because they’ve understood that problem and it’s much more under control. And so, what it really comes down to is the end user themselves. So, as we said, geographically in terms of ambient temperature, the type of asset, but also, the most important thing of course is additives depletion at the end of the day. Because, additive depletion, loss of additive package from the base oil means that oxidation than starts to take place at a greater rate there isn’t inhibitors and antioxidants that can actually control the oxidation. So, yes, it comes down to the end users and of course that means, following the best practice, to avoid the WHAM effect (the water, the heat, the air, the metal) so we simply want to have good, clean systems, free of wear metals, free of solid particle contaminants that cause wear metals, free of air, free of moisture and kept out of unnecessary heat. And that I want to stress, unnecessary heat, because in places like the Middle East, I often see oil stored outdoors in the middle of summer. And we are not talking of the end user necessarily, sometimes at the actual supplier/distributor. So, some of these oils are being stressed even in storage before they go into the machine. So, I think that would safely conclude our root causes. So, when we talk about failure modes, its causes and symptoms, I think next thing would be probably to try to understand what the varnish actually is, and therefore how it leads to failure modes that it causes.
