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By Phil Grellier, Dow Corning

Failure of stainless steel threaded connections can have massive knock-on consequences. Dow Corning’s Phil Grellier tells O&G how these failures can be reduced by simply choosing the right anti-seize paste.

“Traditional pastes contain sulfur, phosphorous, zinc and lead-based compounds that can cause stress corrosion cracking and embrittlement”
-Phil Grellier, Global Strategic Marketing Manager, Dow Corning

When engineers at an oil drilling company started experiencing unacceptable failure rates in stainless steel threaded connections on its massive oil drilling equipment, the situation created some serious problems. Each time the stainless drill components had to be removed from service for repair at a specialty machine shop offsite, the firm not only incurred the expense of extra labour, shipping and refacing the damaged threads, but it also lost the critical sections for up to a week of field service.

Steerable rotary drilling systems are comprised of multiple segments, with critical sections made of stainless steel. Each stainless component is secured with 4-1/2" or 6-5/8" API threaded connections, tightened to standard torque values of 32,000 and 62,000 lbs- ft or 43,400 and 84,100 Newton metres (Nm) respectively.

As this company moved toward commercializing its newest generation of rotary steerable drilling systems, one of its design teams consulted with Dow Corning to investigate a possible reason for the thread damage: a traditional anti-seize paste appeared to be failing under the immense torque required to assemble the components. The investigation revealed the traditional anti-seize pastes contained a number of different metal-based lubricating solids, including chromium, copper, nickel and molybdenum. Stainless steel also contains molybdenum, chromium and nickel, which do not readily react with oxygen; therefore, only very thin metal-oxide layers are formed. Once the oxide layer is damaged by abrasion the oxide-free metal seizes under extreme pressure.

Additionally, the solid lubricants found in the traditional paste re-form oxide layers, which are again removed during abrasion. This cycle continues in a manner where oxide layers and particles build up, clogging thread clearances so the metal components cannot be disassembled. Also traditional pastes contain sulfur, phosphorous, zinc and lead-based compounds that can cause stress corrosion cracking and embrittlement. Both lead to grain-boundary cracks which propagate until bolt fracture occurs. According to this company’s records, failure rate was around 25 percent.

Finding a Solution

Dow Corning and engineers of this drilling company worked together to develop a list of criteria for the  application. They knew they would need an anti-seize compound formulated to provide adhesion to the stainless steel connections that could create and maintain an effective lubricating film despite the extreme loads, contaminants and temperatures of an oil drilling environment. Further, the formulation should have low sulfur and halogen content, with a minimum of phosphorous, zinc, lead and other metals that can contribute to stress cracking or embrittlement.

The replacement material selected was Molykote P-37 Paste that forms a continuous lubricating film with high contact adhesion that withstands extreme forces of drilling applications, contributing to excellent sealing and facilitating disassembly without thread deformation. In fact, the formulation has proven so successful that the drilling equipment manufacturer reports an immediate drop in thread-related failures of more than 50 percent.

Molykote P-37 achieves excellent load-carrying capacity and temperature range of -40°F to 2550°F (-40°C to 1400°C) by containing a synergistic blend of metal-free solid lubricants delivering outstanding seize protection, even under severe operating conditions. Molykote P-37 is approved for use on threaded connections by power plant turbine and steam valve manufacturers, which are notoriously difficult lubrication applications.

Molykote P-37 Anti-Seize Paste delivers outstanding purity for critical applications, containing less than 200 ppm total halogen content (including chlorine, fluorine and bromine) and less than 500 ppm sulfur content (sulfur contributes to stress corrosion cracking). Additionally, Molykote P-37 Anti-Seize Paste’s high purity metal-free solid lubricants result in better protection from solder embrittlement, making non-destructive disassembly more likely.

The odourless, grey metal-free paste is extremely stable under difficult service conditions, giving it excellent durability. It is not classified as hazardous waste upon disposal, and poses no known health or environmental risks from transportation or use. Standard personal protection (safety glasses at minimum) and industrial housekeeping procedures are recommended.

The result is that Molykote P-37 Anti-Seize Paste has proven its ability to form a durable lubricating film in threaded connections requiring 32,000 and 62,000 lbs- ft or 43,400 and 84,100 Newton meters (Nm) of torque. Drilling engineers have found that the lubricant adheres tenaciously to the stainless steel components, facilitating easy disassembly when required and helping to reduce failures.

Phil Grellier is Global Strategic Marketing Manager for Dow Corning and based in Europe for the MRO Markets, where oil and gas is one focus segment. His is a trained industrial chemist with specific experience in electro-coating metallurgy and corrosion protection and has spent 28 years with Dow Corning working within engineering or maintenance applications of Dow Corning and Molykote products. He has also worked in technical sales, commercial management, strategic marketing and solutions/service development.