High alloy lockwire 1

[geesaman.d]

My company supplies components in a variety of alloys. 95% is carbon steel, 304SS, or 316SS. We have 316 SS on hand that we use for lockwiring these.

When we supply higher alloys (C-276, 317L, 904, 2205, 2507, AL-6XN, etc). Getting a small quantity of lockwire is a real pain, often we're left using weld wire that's not formable enough to form quality locking function. Plus many of these materials are still quite hard to form in annealed condition. Hoping to simplify life and stock a very high alloy lockwire material that is soft and workable.

Is there a commonly accepted and available high alloy material for lockwire? Nickel 200 seems promising but appears to be a custom order. Nichrome seems to be very available but I'm not sure if its corrosion-resistance is well documented.

 

[geesaman.d]

does it matter if the lock wire corrodes over time ? inspection reveals lockwire broken, check fasteners and replace lockwire.

Sure there's a production impact, but "surely" you're going into these tanks on a "regular" basis ? Maybe replace lockwire when tank opened ? (in certain severe environments)

Stopping production, clearing toxic vessel, and establishing confined space every few years just to save $50 on lock wire? Let the lock wire corrode and feed down into the downstream pumps and valves? My customers would never consider it, and I would never propose such a thing.

The discussion of crevice corrosion and strain hardening sensitivity is a nice point to help my customers entertain higher alloy options. Odds are good the project managers/project engineers would rather say 'no' and point to the MOC on the equipment datasheet so they can skip having a conversation with their corrosion SME. But if we have a couple of premium alloy options that are more noble than the specified MOC that should hopefully be considered a value-added item.

David

 

[MintJulep]

Then I'll take a step back and ask

What problem are you trying to solve with lock wire?

Because stopping fasteners from getting loose is not something that lock wire does. This is well documented. faq725-1549

Are you trying to keep things from falling off and getting into downstream equipment? If it get's to the point where lock wire is doing this, then something has already failed, and that something really should be fixed.

Wouldn't it be better to look at the design and try to eliminate the failure mode, rather than trying to mitigate the consequences?

 

[rb1957]

lock wire requires a lot of ductility, yes? Are cotter pins more tolerant (to lower ductile alloys) ?

I can see why you wouldn't want corrosion products or bits of wire falling in the process stream (although you didn't specify such).
why not use other locking means ? (like tabbed washers ?)

another day in paradise, or is paradise one day closer ?

 

[TugboatEng]

Tabbed washers are subject to the same failure modes and are a total PITA to install or remove.

All other lock washer types have features that allow the process fluid under the head of the fastener which can lead to seized and broken fasteners in corrosive applications.

As the field guy, adhesive retainers are a major cost burden due to the labor of cleaning up after them.

I have graduated to putting spacers under the heads of problem fasteners.

 

[geesaman.d]

Then I'll take a step back and ask

What problem are you trying to solve with lock wire?

There's not a problem with building our equipment without lock wire. We have durable fastening methods involving oversize hardware with double-nut, Flexloc nut, and/or Loc-tite. Lockwire is an item that some customers require and adding it does not present risk or labor for us, only some cost that the customer covers.

But sometimes we find ourselves scouring the ends of the earth to get a special alloy of lockwire for just one job. This is where it's my job to say "there must be an easier way". The problem is a sourcing / inventory issue with technical factors.

At this point I have no reason to entertain alternate locking methods. If the customer spec says lockwire, I provide it. If it does not, I do not.