leak paths due to excessive inclusion level

[grouse1]

I'm looking for references/information on the impact of non-metallic inclusions on maintaining a hermetic seal. We recently began developing very small leaks in steel fittings (1018)...they are detected after assembly during a helium leak check....post bubble chamber testing shows very slow leaks directly through the fitting. The only difference I note over time appears to be an increase in the density of MnS inclusions. This problem seems to cut across several part numbers from several suppliers. Am I barking up the right tree in thinking that we may need to specify a cleaner steel (lower sulfur) ?? This problem seems to be recent and has me wondering about the steel bar quality in general.

Thanks

Mark

 

[EdStainless]

You are looking at one of the key items. The others involve the amount of cold reduction on the bar in process to break up any semi-continuous inclusions.
I have see this in stainless also. A company had made straight pattern valves for years and they passed He leak testing. One day his long time customer asked for a few angle pattern valves and they all failed. They leaked parallel to the center line of the bar.

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Plymouth Tube

 

[swall]

At one of my previous employers, we used to make diaphragm discs by machining them from Inconel or 304 bar. After several leak instances, we instituted incoming QC on every bar by cutting off a piece and doing a hot HCl etch. One of my first job assignments as the new metallurgist. I've also seen a small 440C shaft leak end to end because centerline carbide segregation.