Case Study: ASTM B994 Nickel-Cobalt vs. Legacy PTFE Blue BoltsMarch 6, 2018
We recently received a report from one of our customers on the performance of our ASTM B994 Nickel-Cobalt bolting that perfectly illustrates both the toughness of our coating and the benefit of painting the exposed sections of the bolting after assembly. This customer decided to replace their previous PTFE blue bolt systems with ASTM B994, and they have since reported superior performance of the Nickel-Cobalt alloy when it is exposed to working conditions.
We wanted to share with you our experience of ASTM B994 coating durability post-disassembly. As you know, the 21st edition of API 6A requires API 20E compliant fasteners for closure bolting. ASTM B994 is certainly a trend in the right direction, as the legacy PTFE would typically chip and get visibly damaged by wrenches and socket torque equipment on the bolt heads and threads. The subsequent exposure of the damaged PTFE to moisture and marine exposure would commence the corrosion process.
The Doxsteel Fasteners that we have used in the shop seem to hold up very well to torquing operations. We did not want to sandblast the bolt heads, so we took the extra time to blast and partially paint the piping components prior to bolting together assemblies for final hydrostatic testing. After hydrotesting, we cleaned off everything and then finalized the intermediate coat and then topcoat. When done this way, the Doxsteel coated bolts didn’t undergo abrasive blasting. This leaves the Nickel-Cobalt coating intact under the topcoat of the painting.
Doxsteel does promote putting a sealer or topcoat over the Nickel-Cobalt coating. You will see partially painted assemblies bolted together with Doxsteel coated bolting in the pictures included. The finished pieces have the topcoat paint sealing the Nickel-Cobalt bolt head. These should hold up very well over time in an offshore environment.
The project team sent some assemblies back to us for modification, and we had to break the assemblies apart to perform the modifications they requested. You can see a picture of the bolt heads below. We had to chip off some of the paint to get the wrenches over the bolt heads, and the Doxsteel coating stayed intact on both the bolt heads and the threads. The threads themselves have shown no signs of damage, whereas the legacy PTFE would usually be damaged or compromised after disassembly.
We are supporters of Doxsteel Fasteners and have included your product as an approved option in our general piping specs from a life cycle justification to date. Not overtapping BSDV bolting is an insurance policy as well, as API 20E compliance is the best practice for high bolting industry integrity.