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.

 

[TugboatEng]

Monel is standard for both the aviation and marine industries.

 

[EdStainless]

We had a run of AL-6XN wire made, used it for about 8 years while I was still working there.
I think that they had enough to last them about another 20-30 years.
If I was picking an alloy for this it would either by Monel 400 or C276.

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P.E. Metallurgy, consulting work welcomed

 

[MintJulep]

What's the problem with 304 or 316 lock wire that you need to solve?

 

[TheTick]

Why does the lockwire need to be "high alloy"? The physical challenges on the lockwire aren't changing. You only need chemical and environmental compatibility.

 

[TugboatEng]

304 and 316 lock wires can crack if exposed to chlorides.

 

[dik]

I've only encountered monel... I'm not aware of any corrosion issues with it.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[rb1957]

why not use another anti-rotation device ?

is the application so sensitive to loosening that you can't use something as low tech as witness marks ?

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

 

[TugboatEng]

Monel wire isn't expensive, is readily available, and works for almost every exposure type.

 

[geesaman.d]

To answer a few questions:
1) These fasten rotating components that live within a pressure vessel. Our customer specifies the material of construction. Occasionally they request the hardware to be a higher grade than the base components but usually they are the same. Once assembled inside the pressure vessel, it is very costly to manually check the hardware. Our standard design works fine with double-nutting but some customers require lockwire too. I believe one advantage of lockwire is visual inspection at a distance.
2) Monel is a good option, but our customers rarely request it as an overall MOC, so I'm not sure how many will like it for lock wire. I'm not sure if PREN is the right way to compare but it might be a good start. I figured pure nickel would be a very safe material based on formability, heat tolerance, and corrosion resistance.
3) Yes, we need chemical and environmental compatibility. As I mentioned before, the alloy choice comes from the customer. 316 Lock wire works great for applications requiring 316, 304, or carbon steel. The lockwire material in question would only be for higher alloy requirements.

I have to believe my lockwire-loving customers keep spools of it in their warehouse since they aren't buying replacement wire from us. It would likely be a one-size-fits-most material grade. That was my hope for our practice, instead of trying to perfectly MOC of the major components.

 

[TheTick]

In what way is 316 not chemically compatible with high alloy steel or anything else your environment?

Worked at a couple places where the supply chain nerds calculated it was cheaper to stock only higher-grade hardware than to maintain duplicate stocks of lower-grade stuff. Lockwire seems a good candidate for such a scheme. Just buy a big spool of Monel and use it for everything.

 

[TugboatEng]

Tick, for those of us in coastal environments the chlorides can cause issues even with 316ss. As chloride containing droplets evaporate the chlorides become super concentrated which can cause corrosion and cracking. Cold working stainless alloys also reduces their corrosion resistance.

 

[rb1957]

"I believe one advantage of lockwire is visual inspection at a distance." witness marks also permit remote verification.

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

 

[TheTick]

Thanks, Tug.

I'm more curious about this specific use case. It seems the only thing that changed was the hardware grade, not the environment. In that case, high-grade lockwire makes no sense.

 

[geesaman.d]

In what way is 316 not chemically compatible with high alloy steel or anything else your environment?

There is no one environment. 316 SS is the most popular MOC, but some customers have extremely corrosive tank contents. TugboatEng's example is one of many situations where 316SS will not hold up. I've designed equipment in Nickel 200, Monel, C-276, AL-6XN, Titanium, G-30, G-35, Inconel, etc.

Decades ago Monel 400 was a very popular high alloy. I rarely see it requested anymore, probably because customers who develop a process test the palette of modern, less expensive stainless alloys. But that doesn't mean Monel won't work.

 

[EdStainless]

The life of lockwire is more severe than other components in the system.
First the holes for the wire to pass through and the tight twists provide superb crevice corrosion initiation sites.
Secondly portions of the wire and heavily worked and stressed.
Both of these issues make 316 very prone to CSCC or pitting attack.
The duplex alloys are no go because even annealed they are very strong (>65ksi yield) making using them a pain.
The 6%Mo alloys are a little better but still rather strong.
When I was in the wire business, I only recall us making five alloys for lockwire: 409 410 or 420 (used for rural outdoor applications), 316 (80% of use), M400 (marine), 625 (used for high temp), and C276 (usually mixers and valves in chemical service).
The reason that I listed 409 410/420 is that we made lockwire and lashing wire (for bundling communications cables) the same way.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[geesaman.d]

Hi Ed,

Isn't C276 also a pain to use?

 

[EdStainless]

Not as bad as AL-6XN, but it is tougher to work with than 316 or M400.
The aerospace spec for M400 soft wire is AMS 4730.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[rb1957]

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)

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

 

[TugboatEng]

If the conditions require lockwire to prevent bolts from falling into the process, maybe you don't want the wire falling in, either.

The lockwire has very little surface area relative to the rest of the system so it's imperative that it be the most noble alloy. If the lockwire less noble than the rest of the system it will waste and fail quickly by galvanic corrosion.