using 18-8 stainless material callout 3

[Tenkan]

I sometimes specify using 18-8 stainless as a material callout where an exact SS is not necessary and I want to give the vendor/machinist options for using material in stock, especially for small qty orders. I realize some of the 18-8's are not as preferred for machining but doable. My logic is if I'm ordering one or two parts why not give the most options for material when possible which the vendor might have in stock as remnants. I understand 18-8 generally applies to 301, 302, 303, 304... any stainless with at least 18% chromium and 8% nickel

This sometimes leads to confusion from vendors with a range of questions from 'which one' to 'can I use 303'...

My question is, is calling out 18-8 material for machined parts bad practice?

 

[MintJulep]

Your logic makes perfect sense to me.

And you seem to be blessed with vendors who will actually call you to clarify.

Another thing you could do is explicitly list them all.

Material: Stainless Steel per ASME 301, 302, 303, 304...

 

[dgallup]

18-8 is only nominally 18% chromium, that is not a minimum. I suppose if your application is that non-critical you can specify anything you want. In general, it is good practice to make material specifications as open as possible as long as it doesn't affect function or safety.

My biggest problem with "18-8" is that it is not a specification at all. Everybody knows what it is but how do you prove what is or is not 18-8? To the best of my knowledge, no standards organization has a precise definition of what is acceptable.

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[ctopher]

You could also make a note "See PO". I have seen this before for parts like this. Add the material that is agreed upon on the PO.

Chris
SolidWorks 11
ctopher's home
SolidWorks Legion

 

[Tenkan]

My biggest problem with "18-8" is that it is not a specification at all. Everybody knows what it is but how do you prove what is or is not 18-8? To the best of my knowledge, no standards organization has a precise definition of what is acceptable.

I think here-in lies the heart of my problem. Without a proper definition it would be bad practice to use this as a callout, but it was always my understanding that 18-8 is used interchangeably when referring to 300 series stainless steel (having approximately 18% chromium and 8% nickel). It is used often in hardware callouts, why would it not be defined somewhere?

And thank you for clarifying 18-8 is a nominal value, not a minimum. (my underscore was not in vain)



lightweight, cheap, strong... pick 2

 

[drawoh]

Koda94,

If you do not care what kind of stainless steel they use, why not just say "STAINLESS STEEL"? If you insist on maximum corrosion resistance, you can say "STAINLESS STEEL AUSTENITIC".

I have just released a drawing specifying "STAINLESS STEEL MAGNETIC". That gives me a ferritic material like 416. I want it to be magnetic. I don't need high strength.

JHG

 

[MechNorth]

Really hate when someone has to go to second or such documentation to figure out part of the product definition, so I never advocate putting "See PO". There's too much opportunity for someone (buyers, being evil buggars that they are) to put in something to save money.

List specific grades that are acceptable on the drawing, or the category such as "Any 300-Series St.St."

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[MintJulep]

but it was always my understanding that 18-8 is used interchangeably when referring to 300 series stainless steel (having approximately 18% chromium and 8% nickel). It is used often in hardware callouts, why would it not be defined somewhere?

18-8 is a colloquial specification.

It's fine for tea kettles and frying pans, but shouldn't be used in engineering call-out where what the material is is important.

18-8 is nominal 18% chromium and 8% nickel. But there is no control at all about what else might be in the mix, or how much of it, and some elements can have undesirable effects if present in more than trace amounts.

 

[Tenkan]

But there is no control at all about what else might be in the mix, or how much of it, and some elements can have undesirable effects if present in more than trace amounts.

This correlates with dgallop's post. it makes sense that 18-8 might be bad practice to use as a material callout.

If you do not care what kind of stainless steel they use, why not just say "STAINLESS STEEL"? If you insist on maximum corrosion resistance, you can say "STAINLESS STEEL AUSTENITIC".

I think this will be the best solution.

To clarify, I'm not getting called every time. I figured that if my callout is questioned at all I should consider if there is a better way to call it out. It doesn't look like 18-8 is a good choice.

lightweight, cheap, strong... pick 2

 

[fcsuper]

I did the research at one time to get all the standards for all the materials my company used, and placed those in the notes. As with the drafting standard itself, any reference to a material should include the national/international standard that defines that material.

Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion

 

[ctopher]

MechNorth,
I agree. I'm not a fan of "see PO", but have seen it done.
In today's world it seems that anything goes. Technical minds don't run a lot of engineering companies anymore.

I prefer to indicate the exact material needed.
The material spec should follow.
If you need 18-8, indicate it. If others are OK, indicated them also as "or".

Chris
SolidWorks 11
ctopher's home
SolidWorks Legion

 

[ewh]

I agree with most here and have often used "300 SERIES STAINLESS" as a callout, leaving it fairly open.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[drawoh]

ctopher,

See Tips on Designing Cost Effective Machined Parts.

The point Joe Osborn make is that when you say just "STAINLES STEEL", he selects the cheapest, easiest to fabricate stainless steel he can find. You both save money.

Insist on specific material only when it matters to you.

This is not just a money saving point. Once it is understood that you are anal retentive about material, it will be assumed that you are always anal retentive. It will be understood that the material can be switched when convenient. The material will be switched when it actually matters to you.

An advantage to being flexible about specifications is that when you aren't, most people will know that you mean it.

JHG

 

[KENAT]

drawoh - we used to just say things like 'STAINLESS STEEL' for situations where there was no load on the part, not particular corrosion concerns etc.

However, purchasing were concerned the machine shop might try using some exotic material they had on the shelf and charge us accordingly so now we spec 303 SST for every non critical situation regardless.

I still find it hard to see purchasing's point but there you go.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ewh]

Once it is understood that you are anal retentive about material, it will be assumed that you are always anal retentive.

Unfortunately, "material" can be substituted with just about any term.
;-)

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[dgallup]

Assuming purchasing did their job and got at least 3 quotes on every job it's hard to see how they could find 3 vendors all trying to gouge you for unobtanium.

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[KENAT]

Ha, ha - 3 quotes. Do they have unicorn parking in your place dgallup;-).

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[dgallup]

Got rid of the unicorns, too impractical. We have flying cars now.

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[btrueblood]

Here's where they dgallup's company sent their now surplus unicorn herds:

http://www.thinkgeek.com/caffeine/wacky-edibles/e5a7/?srp=1

And on a slightly more serious note - the machining cost savings of 303 are more often than not offset by the typically cheaper cost (because I guess so much more of it is used) of 304/304L stock. I usually make the generic stainless callout read "any AISI/SAE type 3xx", or sometimes use "Any UNS S30xxx alloy steel".

 

[ewh]

Oooo, oooo! Soylent Green is back in stock!

Technically, the glass is always full.