[Piercy20]

Good Morning All,

I have be tasked with making some repairs on a cylindrical 4140 P110 part. These parts are used in oil and gas wells. Long story short, there are some protective plates that mount to the outside of the part via threaded holes. These threads have been striped out over repeated assembly. The threads are 3/8"-24 and the stud is 5/8" OD. Thread depth is .4". Some Images should be attached in this post, so hopefully this makes sense.

My intentions are to:
1.) Clean and prep
2.) Fill the threaded holes with Tig
3.) Have the machinist set back up on the parts and drill and tap new holes

I am looking for some guidance on:
-What filler metal to use (I currently have ER70S6 and ER 70S2) I have used these before to preform minor surface repairs on 4140. But I'm not sure if this is the correct filler metal to use.

-Should the part be pre heated to prevent any cracking as the weld cools? I have access to an oven so the parts can be slowly heated and cooled.

-Would it make more since to mill out the existing damaged threads and just fill in the holes this way? This idea makes me think the weld area would be cleaner with just a straight hole instead of dealing with the potential of having contaminants hidden in the thread profile.

Any tip and suggestions are appreciated!

Thanks,
John

[Spartan]

Definitely have those threads milled out if you have easy access to such. They look quite crusty. Milling fresh surfaces will absolutely make your job easier. I weld a lot of 4130, but I don't weld much 4140 at all, so I'll leave the other questions up to more knowledgeable folks.

[Toggatug]

I'd try a helicoil insert on that before I would think about welding it.

Might even be able to get away with a rivet nut depending if the diameters match up etc.

if space allows I would install a stud with red loctite after the repair so that the aluminum doesn't take the abuse as much during re assembly/disassembly

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[Spartan]

I'd try a helicoil insert on that before I would think about welding it.

Might even be able to get away with a rivet nut depending if the diameters match up etc.

if space allows I would install a stud with red loctite after the repair so that the aluminum doesn't take the abuse as much during re assembly/disassembly

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I highly doubt that the customer spec would allow for anything other than welding and remachining to the original spec.

It's possible they would allow it...but those designs typically go through very stringent and lengthy approval processes. Those parts and systems are big $$$$.

[Toggatug]

I'd try a helicoil insert on that before I would think about welding it.

Might even be able to get away with a rivet nut depending if the diameters match up etc.

if space allows I would install a stud with red loctite after the repair so that the aluminum doesn't take the abuse as much during re assembly/disassembly

Sent from my Pixel 3a using Tapatalk

I highly doubt that the customer spec would allow for anything other than welding and remachining to the original spec.

It's possible they would allow it...but those designs typically go through very stringent and lengthy approval processes. Those parts and systems are big $$$$.

Your probably right. I'm just used to make it work by whatever means necessary/able at our shop.

Either way though on that note wouldn't any repair have to be engineered and certified?

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[Spartan]

I'd try a helicoil insert on that before I would think about welding it.

Might even be able to get away with a rivet nut depending if the diameters match up etc.

if space allows I would install a stud with red loctite after the repair so that the aluminum doesn't take the abuse as much during re assembly/disassembly

Sent from my Pixel 3a using Tapatalk

I highly doubt that the customer spec would allow for anything other than welding and remachining to the original spec.

It's possible they would allow it...but those designs typically go through very stringent and lengthy approval processes. Those parts and systems are big $$$$.

Your probably right. I'm just used to make it work by whatever means necessary/able at our shop.

Either way though on that note wouldn't any repair have to be engineered and certified?

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A part like that likely has an approved repair procedure already in place. Many parts such as that are used for years, if not decades, and certain repairs are common and expected. "Recertification" after the repair would likely consist of QA signatures from the people doing the approved repair, and possibly a visual inspection from a QA-type supervisor before the part is put back into service.

[BugHunter]

In some applications, a helicoil is actually stronger than the original thread. For instance, in aircraft engine applications, every hole is helicoiled right from the get-go when brand new. I'm not sure if that applies in a situation where 4140 steel is concerned.

I know if it were an option, I'd go for a Helicoil or Twinsert or whatever brand you like, vs welding. Jmho.

Repairs like this typically call for a lengthy procedure to make the part right, but you'll run into people who've done the repair 100 times who took numerous shortcuts and did just fine, and they'll tell you just weld it up and go. I'll be surprised to hear how welding on 4140 goes, then expecting a machinist to re-drill and tap that hole. I think you'll find that 4140 gets pretty hard near the weld and you're asking a lot to drill and tap it then. I"m not sure how large the part is, but I'd probably make another one before I'd try to repair it.

[Spartan]

For sure there's great benefit in using helicoils to strengthen the threads in some of the softer and/or more brittle metals like AL or some cast iron, but I'm not sure how useful they would be in the higher-grade steels. I don't think I've noticed them being used in that application, but perhaps they are in some industries. Curious if anyone is doing so.

I might be biased, though. I have never liked helicoils and tend to avoid them when I can...even for AL applications. I just tap 2-3x the needed depth if I have the room to make up for the strength and durability loss. For completely non-critical applications, of course...

[Toggatug]

I'm used to heli coil repairs/OE for all sorts of things.

Mount points on the coolers/rads I work on is the most common I see.

I suppose in the high strength steel area it would be of no benefit to use a heli unless it was made of the same or higher grade of steel which I'm not sure if anyone manufactures that.

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[nelson]

Mmmmmmm... helicoil good.

[BugHunter]

I suppose in the high strength steel area it would be of no benefit to use a heli unless it was made of the same or higher grade of steel which I'm not sure if anyone manufactures that.

I'm not trying to say it'll be stronger, just that it will still work.

[BillE.Dee]

piercy, that looks like some type of blind hole insert. What would happen IF you grind down the head and punch it out? I wouldn't think you can't hurt it, it's already broke. You might get it all welded up, send to shop for machining and right in the middle of tapping, the darn thing lets loose. There will be some new vocab used. had a guy up here weld a coil tubing unit reel back together. Can't remember what wire he used but it was stick welded.

[Toggatug]

I suppose in the high strength steel area it would be of no benefit to use a heli unless it was made of the same or higher grade of steel which I'm not sure if anyone manufactures that.

I'm not trying to say it'll be stronger, just that it will still work.

Nah I gotcha. I was just musing that it would be fruitless if those threads see extreme forces which would cause a mild steel insert to rip apart etc.

Like most things in life though we'll never know unless someone does it to see what happens

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