Project Sales Corp –Product Information Bulletin
An Important Contribution towards Operational Safety in Power Stations
MOLYKOTEP 37 Thread Paste Sets New Standards
With a view towards the greatest possible operational safety, particularly high standards have to be met by the materials used in power stations. These also include lubricants, particularly those for bolted connections.
Bolted connections are in some cases exposed to extreme temperatures, which can reach up to 330°C in plants operated using nuclear power and up to 950°C in gas turbines. Such bolts must therefore be made of heat-resisting and high-temperature steels, for example nickel-based alloys, in order to guarantee adequate strength even at such highoperating temperatures. The surfaces of these steels, as a rule, only develop a very thin oxide film. As a result, cold bonding tends to occur when the bolts are tightened or loosened, and so they must be protected with the help of a special lubricant to separate the surfaces. The coefficient of friction should be approx.0.12 to 0.14 order to permit the required uniform tightness of the bolted connections. This is particularly important with flanged connections in order to avoid leaks.
Bolted connections have to be dismantled during regular power station inspections. This, however, is often not possible if an unsuitable lubricant has been used during assembly. The bolts, or studs, then have to be sawn off and the stubs drilled out of the blind hole.This work can take up a lot of precious time. Even greater problems can arise through bolt fractures, for these can lead to leaks at the connected components; these are notifiable accidents in nuclear power stations. Such fractures may be caused not only by metal fatigue but also by the thread lubricant. If, for example, a lubricant containing low melting point metals like lead, tin or zinc, is used the molten metal can defuse into the grain boundaries of the fastener alloy eventually leading to stress fracture. The suspicion exists that even traces of sulphur can cause corrosion on bolts in presence of water or vapour. Halogens, such as chloride or fluoride, can also lead to corrosion of the bolt which may cause fracture.
For the reasons stated above SIEMENS, the power station construction company, stipulates that high temperature bolt lubricants for use in power stations must not contain lead, tin or zinc in their formulation. Any unavoidable contamination by these materials must not exceed 500 mg per kilogram of lubricant. In the past nickel based pastes were sometimes used in bolted connections exposed to high temperatures. Because of the carcinogenic effects of nickel powder, SIEMENS has removed these pastes from their list of approved products.
In nuclear power stations bolted connections are in some cases exposed to radiation and as a result specific ingredients in the lubricant, for example antimony, canthemselves be transformed into radioactive isotopes and begin to radiate. For this reason high temperature lubricants used for such applications should contain no elements, which can be activated at the reactor operation. For these reasons graphite lubricants have been used in the past mainly onscrews exposed to water or vapour. However, due to the lubricating properties typical for graphite,problems occurred after extended exposure to high temperatures. Sometimes bolts could not be loosened and so had to be drilled out.
In 1992 MOLYKOTE and SIEMENS agreed to a joint development programmeto produce and approve a high temperature thread lubricant for power stations which would overcome existing problems. Product development would be in the hands of MOLYKOTE while SIEMENS took over the responsibility for practical testing.
The following were the bolt materials selected for testing as these alloys were considered to be the most widely used in the industry.
•Nr. 1.7709 (21 CrMo NiV 57)
•Nr. 1.4913 (X19CrMoV Nb N III)
•Nr. 1.4986 (X8 Cr Ni Mo BNb 1616)
•Nr. 1.4952 (Ni Cr 20 Ti AI -Nimonic)
The breakaway torques were measured after high temperature exposure at 300, 600 and 850°C. Finally, within the framework of a complete quantitative analysis, the percentage purity of the paste was determined. After completion of the very thorough practical tests MOLYKOTEP 37 high temperature thread paste, which had been developed by this joint project, was approved by SIEMENS for all types of power stations, in accordance with their TLV9600 02/02, for the lubrication of bolted connections in a dry atmosphere.
At about the same time SIEMENS discovered in the course of extensive autoclave tests that MOLYKOTE P 37 was also suitable for threads which come into contact with water or steam. The new thread lubricant meets fully the requirements of power station manufacturers and operators. Its specification does not include any metals, or sulphur, fluoride or chloride. Any contamination from raw materials is far below laid down limits. This high degree of purity is achieved with the help of a special production plant which is solely used for this one lubricant. As an additional safeguard, each production batch is inspected and tested for purity not only on our own premises but also by an independent institute. A purity certificate is enclosed with each delivery. Despite the importance attached to purity, each batch is also checked for mechanical performance as a thread lubricant on a special bolt testing machine before release
.To sum up, it can be said that the new MOLYKOTEP 37 thread pastemakes an important contribution to operational safety in power stations. Due to its ingredients which are non-reactive with bolt alloys, together with its purity and Carefully adjusted coefficient of friction, it protects against seizure of bolts and allows connections to be dismantled easily, even after long periods at high temperature.
Technical advantages of MOLYKOTEP 37.
Good lubrication properties in bolted connections.
Solid lubricants stable up to temperatures of 1400°C.
Contains no metals whatsoever .
Less than 200ppm of sulphur, chloride and fluoride.
Coefficient of friction within the range of oiled bolts.
Purity certificate enclosed
Also approved by GE, P&W, Westinghouse, BHEL, Rolls Royce, Mitsubishi Heavy Industries Ltd, Daimler-Chrysler Aerospace, US Navy Ship Board Turbines, Nuovo Pignone, MTU, Electricity De France, Thai Petroleum Corporation Limited and many more power stations, refineries, and turbine and engine manufacturers around the world.
Now available in imported brush top tins of 500 grams. The packaging of the thread paste in tins with brushes helps to avoid contamination which could occur through brushes that have been used elsewhere.
Ships for Rs. 3250/-per tin plus taxes, with a purity certificate, off course ! Project Sales Corp, 28 Founta Plaza, Suryabagh, Visakhapatnam 530020, APCall +91-8912564393, Fax +91-891-2590482, Mob +91-98851 49412http://www.projectsalescorp.com
