Question about 304SS job and material movement

[eKretz]

So I got a job to quote. Part is spec'd as made from 304SS pipe, 5" SCH 80 welded pipe. That's 5.06" OD and 4.81" ID. Pipe is about 41" long, gets two stub ends welded in. They want it finished at 5.000" +.001"/-0 so only 1/32" per side stock to start as fabbed! I'm worried about movement during the cutting of that OD. 304 always moves quite a bit in my experience. So I would generally expect to solve that problem with thermal stress relief. But then I may end up with a warped part that needs straightening. Which will add stress back in that may get relieved when that outside surface is removed. Ugh. Should have been designed with a thicker wall pipe to start. Oh, and they also want to spin it at 1200 RPM. This is not going to work out well. For their price I mean. Maybe I need to ring them up. What are your thoughts?

 

[Bobw]

Isn't the OD on 5" pipe, 5.56"?

 

[mhajicek]

What are your thoughts?

I'm glad I'm not in your position...

 

[eKretz]

Isn't the OD on 5" pipe, 5.56"?

SCH 80 table I looked at said 5.06" OD 4.81" ID. That does sound awfully thin walled. If that's a typo then I will be much happier. Time to look at another table!

Edit: yep, should have just looked in the handbook rather than using the internet. Dope slap for me. Thanks for pointing that out, Bob.

 

[MrWhoopee]

Yes, 5.56" is the OD.

Stress-relieving will not help with 304. I believe the stresses are due to the very nature of the lattice and the only way to remove them is heat it high enough to allow the nickel and chromium to migrate within the lattice, removing the stainless properties. It will always move, and rarely the way you want or expect.

My experience with this type of roller is that, if you get partial cleanup on the first pass, the pipe will bow towards the cut. Then the next pass takes more off the side that you've already cut and still no cleanup on the other side, causing it to bow more. It can get ugly fast. My best advice is to use oversize shaft, make sure the roll is indicated as true as the pipe will allow, center drill the shaft, turn the OD then turn the shaft.

Good luck.

 

[eKretz]

Yes, 5.56" is the OD.

Stress-relieving will not help with 304. I believe the stresses are due to the very nature of the lattice and the only way to remove them is heat it high enough to allow the nickel and chromium to migrate within the lattice, removing the stainless properties. It will always move, and rarely the way you want or expect.

My experience with this type of roller is that, if you get partial cleanup on the first pass, the pipe will bow towards the cut. Then the next pass takes more off the side that you've already cut and still no cleanup on the other side, causing it to bow more. It can get ugly fast. My best advice is to use oversize shaft, make sure the roll is indicated as true as the pipe will allow, center drill the shaft, turn the OD then turn the shaft.

Good luck.

Yeah I've had the same results. Don't like these longer stainless tubing/pipe jobs but they can usually be done without too much trouble at smaller diameters. Big diameter with this wall thickness would be a nightmare. I have had stress relief work well for 304 but it has to be higher than the normal temp. As I recall there's a low temp and a high temp stress relief. There is a temp range in the middle that needs to be steered clear of IIRC due to likelihood of subsequent stress cracking.

 

[Milland]

Tell them they'll need a way to balance this assembly before spinning it at 1200rpm. It's very likely the ID will not be totally round or concentric with the OD, so unless you're boring the ID round then centering it prior to turning the OD there will be material displacement leading to imbalance.

Good luck...

 

[eKretz]

Yes we'll have to get it balanced.

 

[memphisjed]

4 1/2 " pipe is 5.03 or 5 depending on which chart I look at. sch 80 is 3/8 or .355 wall - again chart dependent. Not that it helps to get true 5 od. Pipe is never round in machinist terms. 5" xxs pipe is 5 9/16 with 3/8- this one I have in my coper list so I am confident that it is a good average.
Dom would be expensive, and not sure what sizes you can get, but the stress will lean linear and not radial.

 

[dian]

maybe use 304L (less corrosion sensitivity)? for dimensional stability my source sais low temp anneal and slow cool. <500°c.

 

[Bobw]

Pipe is never round in machinist terms.

Its barely round by pottery standards.

A roughing carpenter might call it round.. Because its EXACTLY 5 and 9/16".

 

[Bobw]

re-reading this.

Its a conveyor roller isn't it?

There are places that make those day in and day out. You can
even get custom sized rollers at McMaster Carr. Not quite
5" ones, but you can get them.

A 41" long 5" stainless roller is going to be a big nut.

They want to see if you can do it cheaper, and then they toss
on a +1 -0 tolerance. Because tight tolerances prove what good
train drivers they are.

Actually, the tight tolerance is to keep it tracking straight.
Its one of those where the actual dimension could be all over
the place as long as its the same along the roller.

Over here we tend to taper the ends to help center the conveyor,
and then just use the raw pipe OD. And they adjust to get the
conveyor centered, since each end of the roller is independently
adjustable with a take up. Also not running 1200 rpms, maybe 500
on the high end.

 

[eKretz]

No, it's some sort of rotary brush mandrel I believe. Definitely not a conveyor roller. The stubbed ends are completely different and have bronze bushings pressed into bores in the ends.

 

[BT Fabrication]

pipe like that is never round, always oblong. unless you turn the outer diameter first.

have had 2" pipe sch 40 that is anywhere from 0.015" to 0.027" out of round 90 degrees from each other.

good luck to his pocket book.


5.563-0.375-0.375 =
so about 0.093" wall thickness left over?

 

[Bobw]

pipe like that is never round, always oblong. unless you turn the outer diameter first.

have had 2" pipe sch 40 that is anywhere from 0.015" to 0.027" out of round 90 degrees from each other.

good luck to his pocket book.


5.563-0.375-0.375 =
so about 0.093" wall thickness left over?

And it just get worse, and worse, and worse..

I didn't even catch that..

Might as well just send them a roll of Reynold's Wrap and a bill.

 

[eKretz]

Yep, went with a no-quote.

 

[MrWhoopee]

Yep, went with a no-quote.

Know when to walk away, preferably before the job has gone to sh*t.

 

[Bobw]

Yep, went with a no-quote.

Hi Purchasing Agent...

HAHAHAHAHAHAHAHAHAAHAHAHAHAHAHAHAHAHHHHHAAAAAA!!!!!!!!!!!!!

NO!!!!!!

Thanx
Ekretz.

 

[72bwhite]

Tell us what you really think of 304 pipe Bob

 

[eKretz]

Tell us what you really think of 304 pipe Bob

Thin-walled 304 pipe. We feel much the same way about it, apparently.