Liquid metal embrittlement occurs when extreme high temperatures bring fastener coatings to their melting point. As the coating liquifies, it induces a loss in the bolt’s tensile ductility, causing it to become brittle and highly susceptible to fracture. Fastener embrittlement can occur even when a coating comes close to its melting point, producing a condition known as solid metal embrittlement.
ASTM A194 specifications state that coatings subjected to temperatures higher than one half their melting point are in danger of producing liquid and solid metal embrittlement in the fastener, effectively prohibiting every common and legacy coating system from high temperature bolting operations. As a result, most manufacturers either completely forego coating bolts that are marked for high temperature uses — such as B16 studs that are installed in turbines, manholes, or heat exchangers in refinery and power generation facilities — or they resort to using expensive studs manufactured from Nickel or other exotic metals. Since these high temperature applications are still susceptible to corrosion and seizing, the unprotected bolts have a shorter life cycle than effectively coated bolts in standard conditions, ultimately increasing turnaround frequency and driving up costs from downtime.
If a fastener coating existed that could resist the extreme temperatures that lead to liquid and solid metal embrittlement in legacy coatings, it could greatly reduce the downtime that refineries and power generation facilities experience as a result of fastener turnaround. Such a coating would lead to both significant bolting cost savings for the facility and greater operational efficiency.
Thankfully, such a coating does exist: ASTM B994 SC18 Class 1 Nickel-Cobalt alloy.
Temperature Range Comparison: ASTM B994 vs. Legacy Coating Systems
ASTM B994 SC18 Class 1 Nickel-Cobalt alloy has a melting temperature of 2642°F. Under ASTM A194 specifications, ASTM B994 SC18 Class 1 plated bolts can operate in temperatures ranging from -300°F to 1300°F without compromising their coating. The table below compares these performance statistics with current and legacy coating systems that are still in use for downstream, power generation, and upstream operations. Even the most resilient coating competitor, Zinc-Nickel plating, can withstand only 30% of the temperature range that is possible with ASTM B994 SC18 Class 1 Nickel-Cobalt electroplating.
When compared to other leading coatings with much lower melting points, the difference is clear. ASTM B994 SC18 Class 1 Nickel-Cobalt alloy can go places that legacy coatings cannot. Before ASTM B994, it was preferable to install bolts in high temperature environments without coating protection rather than risk the possibility of liquid and solid metal embrittlement. Now, with ASTM B994 SC18 Class 1, high temperature downstream and power generation operations have a fastener coating system that can protect bolts from extreme temperatures while slowing corrosion rates and maintaining thread engagement, leading to longer turnaround cycles and reduced turnaround times.
Protect Your High Temperature Bolting with Doxsteel Fasteners
In the extreme temperatures that come from downstream and power generation operations such as manholes, turbines, and heat exchangers, Doxsteel Fasteners keep working. Our controlled application of the ASTM B994 SC18 Class 1 coating process produces a bolt that stands up to corrosion and resists seizing longer than any other bolt on the market. Its operational temperature range far exceeds competitor coating systems, and each Doxsteel plated bolt comes with a five year no seize guarantee.
To learn how to protect your bolting from high temperature refinery and power generation environments such as manholes, heat exchangers, and turbines, contact Doxsteel Fasteners today.