Lube Varnish in Hydrogen Seals, What Can We Do?
Varnish exists in all shapes and sizes. Typically, when we think about varnish, our thoughts move towards large pieces of equipment. However, due to the nature of varnish, it usually affects the smaller (or tighter) component clearances first which in turn cause the entire machine to fail. One such component is Hydrogen seals usually found in turbines, generators and lots of other equipment.
Those Hydrogen Seals!
In the past, Hydrogen seals experienced high efficiency losses due to their design. The spring held seals saw higher rates of leakage and led to large cost implications due to this inefficient design. As such, designers wanted a more rigid structure and decided to use bolted seal designs to maintain tighter clearances which should reduce the rate of leakage and increase the efficiency. However, these tighter clearances are more susceptible to varnish! Reduced clearances usually lead to low seal oil flow, increased seal oil temperature and reduced hydrogen consumption. All of these impacts lead to reduce efficiency and possibly loss of production with increased downtime. Seal oils can experience temperatures in excess of 200°F
There are two factors to consider when thinking about varnish control in Hydrogen seals.
We must first think about its proper installation (ensuring that the clearance is adequate) and the second is guaranteeing that the prevention of varnish due to low lube oil quality. If these two can be maintained simultaneously, then we can control the failures of these hydrogen seals. During our investigations, we have found that hydrogen seals have three classifications of varnish. These classifications include; Incipient varnish (the beginning of varnish formation), Propagating varnish (wide spread of varnish) and Critical varnish (where it endangers the reliability of the equipment).
Identifying Varnish in Hydrogen Seals
Let’s talk a bit more about the types of varnish in Hydrogen seals and methods of identifying which type is occurring in your equipment.
This is usually the beginning stages of varnish and the deposits are typically a thin yellow to light brown layer. Even though this is a thin layer, it can significantly impact on the clearances of the seals. This thin layer is not always uniformed hence there will be areas where the flow is disrupted leading to higher and lower flow rates. This can lead to further problems.
The main differentiator of propagating varnish is its darker color with a thicker layer of deposit which disrupts the oil flow. This disruption can lead to cavitation of the seal. Due to the slower oil flow, the temperatures increase quickly as such the deposits formed can be either organic or inorganic. Moreover, the surface of the hydrogen seal usually sees some damage and this can lead to eventual seal failure if not corrected.
The main characteristics of Critical varnish are extensive mechanical damage to the seal and the presence of thermally degraded components. Typically, the thickness, hardness and structure of Critical varnish cause major destruction of the seals. This is mainly attributed to the flow restriction and resulting erosion and wear mechanisms.
Solving the Varnish issue in Hydrogen Seals
It is clear that there has to be a two pronged approach to mitigate the presence of varnish in Hydrogen Seals. Firstly, we need to ensure that the seal clearances are adequate and then we need to guarantee that the oil remains free from deposits. If there are deposits present then this can initiate more deposits to be formed leading to the build-up varnish which in turn affects the clearances of the seals.
One such way of removing deposits is through the use of an ESP (Electrophysical Separation Process). This is a filtration system that uses chemical filtration technology to remove degradation products while not affecting the additive components of the oil. This is used in a kidney system whereby the oil enters the ESP gets filtered and is returned to the system. However, if we treated the oil, such that the solubility of the degradation products increased (stayed in solution), this would lengthen the life of the oil and ensure that the hydrogen seals do not suffer from varnish.
Boost VR+™ (with patent pending Solvancer® technology) is designed to ensure that stubborn deposits get dissolved into the oil and not left behind to form additional deposits. When Boost VR+ is used via Fluitec’s VITA ESP system, it ensures that any deposit stays in the oil (Boost VR+) and then these can be removed using the ESP. Through the removal of the deposits in the oil, this allows more deposits to be dissolved (via the Boost VR+) and then be removed with the VITA ESP system. Thereby, they can remove all the catalytic degradation products in the oil and increase the lifespan of the oil through this cycle.