Galling threads 4

[subsearobot]

I am threading an endcap onto a cylinder- it will be a core sampling instrument. The endcap will take a some large impact loads, so needs to be a strong and tough material. The machine will operate in a marine environment, so 17-4-h900 is the preferred material. the cylinder will be 304SS schedule 80 pipe.

Will this combination lead to a galling problem with the threads? The threaded joint will be made and unmade each time a sample is taken.

I have had some serious issues with stainless galling- especially 316 to 316 joints.

thanks in advance!

 

[btrueblood]

"Will this combination lead to a galling problem with the threads? "

Likely yes. The PH alloys don't offer much more gall resistance than the standard 300 series alloys.

A Nitronic alloy, say Nitronic 60 or 32, or similar anti-gall stainless alloys (Carpenter Gall-Tough) might be a better choice for the cylinder than 304. Both alloy types typically use Si additions to create more gall- and wear-resistant alloys. You should be able to Google on some of the above terms and get a plethora, if not a veritable cornucopia of engineering data.

 

[unclesyd]

I'll wholeheartedly second the suggestion by btrueblood especially the galling aspect of the problem.

It has been my experience that your stated MOC has created some terrible galling problems for me to the extent that the components had to be machined apart.

Here is The HP Alloy site one of many sources of information available for N60.
If you download the 40 page brochure there is some very good information of galling of metals.

http://www.hpalloy.com/alloys/descriptions/NITRONIC60.html

 

[saberblue]

If you want to go this way you may want to look at one of the Teflon filled "pipe dope". These and similar compounds provide a barrier that might prevent the galling

 

[subsearobot]

That was my fear- Since this is a science project, the budget is limited; I think using nitronic for 350# of pipe would be nixed by our clients. I may, however be able to fit a coupling of nitronic between the cylinder and the endcap.

Another consideration is to make the endcap of a non stainless steel. It will get bashed up by rocks in the sediment long before it rusts out.

Back to the galling question: will 304 gall with something like 4130?

cheers,

 

[TVP]

Here are a couple of articles about stainless steel fasteners and galling, including a recommendation for a lubricant that may enable you to keep the parts in stainless steel:

http://www.greensladeandcompany.com/pdf/Problem Solving-Stainless Steel Galling Solutions.pdf

http://www.greensladeandcompany.com/pdf/Problem Solving-Stainless Anit-Galling Lubricant.pdf

 

[unclesyd]

Yes they can gall though not as bad as SS on SS. The application of a baked on dry film lubrication will be big help for your post metal combination. There are some brush on lubricants that can also help but if your are sampling I assume you don't want the risk of contamination.
I wouldn't give up on the Nitronics, keep checking around for the availability.
Yes you can add a Nitronic section to 316 SS stock by welding. Just keep the weld joint at least 3 times the length of the threads away from the last thread to retain the antiglling properties of the Nitronic.

 

[redpicker]

If you go with the Low-alloy steel caps, you can improve the galling resistance by having the threads of the cap phosphate coated (either a Zinc or Manganese Phossphate conversion coating, check with paint vendors as this is usually a step in preparing metal surfaces for painting). Lubricate the threads liberally with grease and torque the caps to the stainless body several times. Inspect the threads after for galling (don't worry too much about the phosphate coating at this point as it is there mostly to insure the grease coats the threads without sliding off.)

This will work harden the thread surfaces and make them much more resistant to galling during use. If you do experience galling, you can repair them and repeat, which would be much better than having it happen during use.

rp

 

[CoryPad]

Great post rp.

 

[EdStainless]

The hardness difference will minimize galling, but a good potion may be to Cu plate the 316. It will act as a lube and help minimize issues.
If you roll thread them this will also help minimize galling.
Use a good anti-seize compound designed for stainless.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[sreid]

Kolsterising?

http://www.kolsterising.bodycote.com/

 

[TEV]

Yes, you will have galling. You need to prevent stainless-to-stainless contact to pevent it. This may be accomplished by using teflon pipe tape, plating the mating surfaces with a soft, deformable metal, and/or using a dry film lubricant such as molybdenum disulfide in a polymer.

Critically important, though, is thread form. The threads MUST be designed and manufactured such that there is NO thread crest-to-root interference. This means proper truncation of the thread crest to clear the root. If you have crest-to-root interference, you will have severed galling no matter what other mitigation steps you take.

Kolsterizing will help very little.

 

[Ron]

What thread profile are you using? How about ACME or similar variation? Works well in impact soil samplers.