RB-24 THE ADDITIVE “rb bertomeu” beco F1/ASF AND THE INCREMENT OF THE USEFUL LIFE
OF REFURBISHED EXHAUST VALVES , IN DIESEL ENGINES USING HEAVY FUEL OIL
rb bertomeu, S.L.
Confirming our opinion, written in our previous article published in July-98, (see complete article) about the viability of using refurbished exhaust valves in Diesel engines , with the condition of using heavy fuel oil with a correct anti-corrosion treatment to guarantee that normal TBO (Time Between Overhauls), foreseen by the Maintenance Department, will be reached without problems, we set out the results of a tests carried out in a Deutz engine installed in a power plant, where has been recently demonstrate that even using refurbished exhaust valves (refurbished from 1 to 3 times), the use of a good fuel treatment like the heavy fuel oil additive “rb bertomeu” beco F1/ASF has allowed , not only reach the normal foreseen TBO (which was not possible before using that additive), but DOUBLING it.
Tests for duplication of the normal value of TBO (Time Between Overhauls)
Date of execution : 2000 – 2002
Engine type : Deutz BV 16M 640
Engine power : 6.3 MWhe
Number of valves : 32
Fuel used : Heavy fuel oil
Reconditioned valves installed for the test (1) : 26 (81.25 %)
New valves installed for the test : 6 (18.75 %)
Fuel treatment : “rb bertomeu” beco F1/ASF
Inspections carried out : 2 intermediate random inspections on 2 valves
1 final inspection over all installed valves
Results : Reached TBO : 203 % of Normal TBO
(normal TBO + 103 %)
(normal value of TBO is doubled)
The test was given as concluded when the objective of duplication of normal TBO value was reached, although was evident that should be
possible to increase the TBO still more. See this letter of reference (in Spanish).
Exhaust valves changed due to blow out , before final inspection: 3
1 Valve at 150 % of normal TBO ( B1A )
1 Valve at 180 % of normal TBO ( A8B )
1 Valve at 190 % of normal TBO ( A5B)
Valves B1B and B8B , were also changed , in spite that it was not necessary, before the test conclusion, to made some studies and controls by Deutz.
Reusable valves find in the final
inspection, at the end of the test : 31 (96.8 %) (2)
Non reusable valves find in the final
inspection, at the end of the test : 1 ( A3A ) (3.2 %)
(1) Valves used previously in other engines, with a number of mechanical rectified
variable between 1 and 3.
(2) Among all valves, 28 had some compactation or hammer signals in the seats , which can be eliminated by a slight mechanical rectified. The other 3 valves had very soft corrosion on the surface of seats , which can be also eliminated by a mechanical rectified slightly more deep than in the previous case.
In the next pages you can find the article published in July-1998, titled "Considerations about the installation of reconditioned exhaust valves in a Diesel engine ............. "
DIESEL ENGINE RUNNING ON FUEL OIL, REGARDING THE USE OF ADDITIVES FOR THE FUEL
Exhaust valves consist basically of two different components, the basket and the spindle, with closure seats , male – female type.
The area of the valve seats is made up of a certain thickness of a special alloy designed to withstand their harsh working conditions: percussion between seats, with particles of solid residues on both faces, chemical attack and thermal attack.
Percussion between valve seats is produced each time the valve closes. Given that the stream of exhaust gases contains a high quantity of solid particles, (Sulphates, Vanadates, etc.) formed in combustion from the impurities in the fuel oil, a large proportion of these particles are trapped between the valve seats each time the valve closes. This causes compacting which produces pitting and deformations on the surfaces of the valve seats. If this phenomenon is detected in general overhauls, the valves may be reconditioned by mechanical correction or rectification, and can be re-installed without trouble.
Chemical attack may appear on the seats of baskets and valves, and due to the compounds formed during the combustion of fuel oil from the impurities it contains (principally sulphur, vanadium and sodium). When the attack is severe the seats of the basket and/or the sleeve are perforated (valve blow-out) and the effect of sealing or closure between the two is lost, and thus the only solution is to replace both components with new ones. Valve blow-outs may also occur due to faulty rotocaps, which may cause a “blowing” effect at a particular point.
When the attack on the valves is slight, i.e. the corrosion is superficial, both components are reconditioned in general overhauls by correction or rectification of the seats, and they may be re-installed as in the previous case.
Thermal attack may appear on the flat surface of the sleeves after several thousand hours in operation. On the valves of Deutz engines, this may occur after 12,000 – 15,000 hours in operation. When acute thermal fatigue is detected, the sleeve must be replaced in order to avoid the possibility of its breaking and causing a major breakdown in the engine. Technically, supposing the fuel oil did not contain any corrosive elements, or if it is treated with additives in order to render them harmless, valves should come to the end of their working lives due to thermal fatigue.
On the basis of the information above, it follows that the components of the valve must be discarded and replaced by new ones for one of these three reasons:
- Severe thermal fatigue.
- Severe corrosion or blowout.
- Removal of the special alloy layer on the valve seats (the component does not conform to size) after successive mechanical corrections or rectifications.
When either of the two components is replaced, considering that engine overhauls are performed approximately at intervals of 3,000 – 4,000 hours in operation, it is immaterial wether they are replaced with new or reconditioned components as it is merely a question of being in operation again for a similar period time:
- If the reconditioned sleeves that are installed are not thermally fatigued, the symptoms will not appear until the following overhaul at the earliest.
- If the rectified seats conform to size, this implies that they have sufficient thickness of special alloy and are thus equally resistant to corrosion as the seats of new components.
- Obviously, a rectified seat will survive fewer overhauls, if it has previously been subjected to a greater number of surface corrections, or deeper surface corrections, due to more severe corrosion.
The additive treatment applied to the fuel oil used is fundamental to prolonging the working life of valves, both new and reconditioned ones. In this respect, the additive must ensure that both corrosion and pitting on the valves are minimised so that the corrections performed in general overhauls may be as superficial as possible. This will minimise the reduction of the thickness of the special alloy, and the working life of the valve will be prolonged over many more overhauls.
We are widely experienced in this field. To give the clearest example of this we may quote a co-generation plant equipped with three Deutz engines which has recently undergone its 26,000-hour overhaul and has used fuel oil treated with our products:
- The original valves have been reconditioned and re-installed at each general overhaul.
- Currently, after 26,000 hours in operation, 84% of the original baskets and 60% of the original sleeves have been reconditioned and re-installed, whilst the manufacturer’s figure for their operational life is of 12,000 – 15,000 hours.
- Of the rest, 60% were replaced at the 26,000-hour overhaul and 30% at the 21,000-hour overhaul due to thermal fatigue of the sleeves or seats that did not conform to size after between 8 and 9 general overhauls.
The conclusion is clear: The fuel oil additive must achieve two objectives in relation to the life of the valves, whether they are new or reconditioned,
A) Extend the operational life to the maximum degree.
B) Ensure that breakdowns due to corrosion do not occur between general overhauls.
© rb bertomeu, S.L. - Pol. Ind. Fondo de Llitera, Par. 82-83 - E-22520 Fraga, Huesca (Spain)