Publié le 2020-02-13
Every time the defective drill sections had to be removed for repair in a specialized machine shop, the company incurred additional costs for labor, shipping and reloading the damaged threads, experienced production downtime and also lost critical sections for a week.
Each stainless steel section of the Noble rotary drilling systems is secured with either 114mm or 168mm API threaded connections. These critical connections are tightened to standard torque values of 32,000 and 62,000 foot-pounds (43,400 and 84,400 Nm, respectively).
Customer: Noble Drilling Corporation, Sugar Land, Texas, USA, is a world leader in oil drilling technology.
Challenge: Prevent cold welding, seizing and failure of stainless steel threaded connections tightened to extremely high torque levels.
Solution: Replace a traditional anti-seize paste, which was pressed out of the high-torque connections and caused thread failures, with an extremely pure solid lubricant that is free of metals, lead, chlorine and fluorine.
Product: Molykote P-37 anti-seize paste
As Noble Drilling prepared to launch its latest generation of rotary directional drilling systems, one of its design teams worked with DuPont's lubricant specialists to identify possible causes of thread deterioration and connection failures. At that time, high-torque connections were made with a traditional anti-seize paste, which facilitated the assembly of many other threaded connections. But this paste was apparently compressed by the extremely high clamping forces.
The problem seemed to centre on the traditional non-stick paste containing various solid metal-based lubricants, such as chrome, copper, nickel and molybdenum. Stainless steel also contains molybdenum, chromium and nickel. These do not react well with oxygen, so only very thin layers of metal oxide have formed on the threaded connections.
If the rust layer is damaged by abrasion, during clamping, the abrasive particles will build up and the rust-free metal will freeze under extreme pressure. The resulting obstructed threads then prevent easy disassembly of the couplings, which has been identified as the main cause of bolt failure.
Another cause is that many common anti-seize pastes contain compounds based on sulphur, phosphorus, zinc and lead. This might cause stress corrosion cracking and thread brittleness. Both conditions can result in grain boundary cracks in metal fasteners and screw threads that propagate until bolt failure occurs. According to Noble, their bolt failure rate has reached 25%.
Molykote's lubrication specialists and Noble Drilling's engineers worked together to develop the criteria needed to reduce the unacceptable bolt failure rate.
First, the anti-seize paste had to provide superior adhesion to stainless steel components. It must also maintain an effective lubricating film despite the loads, contaminants and high temperatures of an oil drilling environment.
In addition, the formulation must be low in sulfur and halogen, with a minimum of phosphorus, zinc, lead and other metals that can cause stress cracking or brittleness of metals.
The solution chosen was Molykote P-37 anti-seize paste, a high-purity, metal-free solid lubricant specially designed for stainless steel threaded connections. The high viscosity paste forms a continuous lubricating film with strong contact adhesion that withstands the extreme forces of drilling applications. It stays in place under extremely high clamping forces, provides excellent sealing and facilitates component removal without thread deformation.
Noble Drilling has replaced its traditional non-stick paste with Molykote P-37 in the critical stainless steel sections of its rotary swivel drilling equipment. This efficient solution made a big difference in increasing system reliability, reducing costs and maintaining production schedules. Noble reported an immediate decrease of more than 50% in wire-related connection failures.
The paste chosen to solve the problems of thread seizure has an excellent load capacity over a wide temperature range of -40°C to 1400°C. It contains solid metal-free lubricants that provide exceptional protection against seizure, even in difficult oil drilling conditions.
Molykote P-37 paste is also used in threaded connections of power plant turbines (available in PMUC version) and in steam valves, making lubrication difficult.
Molykote P-37 paste has a total halogen content (including chlorine, fluorine and bromine) of less than 200 ppm and a sulphur content of less than 250 ppm. Its high-purity, metal-free solid lubricants protect against cold welding, scraping and brittleness, allowing for non-destructive disassembly.
The odourless grey paste is extremely stable and has excellent durability. It is not classified as hazardous waste when disposed of and presents no known health or environmental hazards during transportation or use.
Molykote P-37 is available in :
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Source : www.dge-europe.com
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