304 to 316 on pullpit

[John Dickie]

I'm fabricating a pullpit and can't get tight radii in 25mm 316 tube.The options are a mitre or weld in a 304 bend.I'm told it will be fine;I'd just like other opinions.Thanks.

 

[jehardiman]

It will be OK with TIG and the correct filler, just don't use iron/steel tools on it.

 

[fallguy]

I'm fabricating a pullpit and can't get tight radii in 25mm 316 tube.The options are a mitre or weld in a 304 bend.I'm told it will be fine;I'd just like other opinions.Thanks.

I have fab work planned and we are hoping for 3-4.5" radii with 316.

How tight were you trying and failing, if I may?

 

[Barry]

I'm fabricating a pullpit and can't get tight radii in 25mm 316 tube.The options are a mitre or weld in a 304 bend.I'm told it will be fine;I'd just like other opinions.Thanks.

Go with 316 as it has a higher resistance to saltwater corrosion. More expensive of course due to its higher Chromium percentage.
Just Google, Corrosion Resistance Between 304 and 316 Stainless in Saltwater. Lots of articles from layman's terms up to the metallurgy

 

[jehardiman]

Go with 316 as it has a higher resistance to saltwater corrosion. More expensive of course due to its higher Chromium percentage.
Just Google, Corrosion Resistance Between 304 and 316 Stainless in Saltwater. Lots of articles from layman's terms up to the metallurgy

If we where talking about the bolting pads of the pulpit to the deck I would agree for the superior crevice corrosion of 316l or 316 ELI; but for a welded railing tube...not one whit of corrosion difference as long you don't embed iron filings in the stainless. Generally it is the cutting debris that corrode, not the base metal. That's why so many spoons and forks are 8-18, but no knives.

 

[John Dickie]

I have fab work planned and we are hoping for 3-4.5" radii with 316.

How tight were you trying and failing, if I may?

I asked for 3",but when they realised it was 316 they said they would need a "ball mandrel"

 

[fallguy]

If we where talking about the bolting pads of the pulpit to the deck I would agree for the superior crevice corrosion of 316l or 316 ELI; but for a welded railing tube...not one whit of corrosion difference as long you don't embed iron filings in the stainless. Generally it is the cutting debris that corrode, not the base metal. That's why so many spoons and forks are 8-18, but no knives.

I am talking about seamless railing tube.

Figured I need 316 and it is nowhere around these parts.

 

[Rumars]

While I agree that a properly electropolished and passivated 304 bend is no real problem, it's not like the fab shop doesn't have other options if all 316 is desired.
1. Use a solid bar to make the bend and weld it in.
2. Fill tube with dry sand (or wet sand then freeze it), cold bend and weld in.
3. Sand packed hot bending.

 

[jehardiman]

OK, there is a real limit for minimum radius bending hot or cold. 2.5 d pops to mind but I would need to check. Lots of special machines/processes to prevent tearing of the material. No straight answer with the given information.

 

[Rumars]

Sure, but it's not about the minimum radius here, it's about the ball mandrel. If they figure they can bend it cold using one, they can also bend it by using other means of internal support, like sand or ice packing.