Stainless Steel Properties

This would depend on whether the purchaser or specifier of the valve will allow 304SS. 304 and 316 are similar BUT NOT identical stainless products, and may not be interchangable for the end user.

I would be very cautious on changing the material.

That's true. However if the grade of stainless steel has never been specified then it can be left up to the manufacturer to decide.

I would imagine the reason for this question is because of the price instability from the fluctuation in the cost of nickel.

If that is the case and 304 is acceptible then if it is available in his area he might as well go to 201 SS.

201 has less nickel and has the same corrosion resistance as 304. It handles the same as 304 and is stronger in tensil strength. Its advantage is that because it has less nickel it is more stable in price.

201 is also USDA Food grade certified. Much of your food processing surfaces are 201 SS.

There is a lot of interest generated in 201 because of this.

I'm not familiar with patroleum product processing. I don't think it would be that corrosive. The company I work for manufactures machinery used in produce packinghouses and tomatos have a high acidic content that requires stainless steel machines. We use 304 primarily. 201 isn't available on the west coast yet. We also have some material that is 316 but that is because some forms of SS is restricted to that particular grade. Such as 416 SS can only be obtained in sheets.

When in doubt, contact the customer and ask them. Check the contract and see if there is any stipulation about grade. When ever I subcontract a part I always specify the material in my quote request, even though the drawing has a material listed and I tell them to pay attention to what is in my request not on the drawing.

"201 is also USDA Food grade certified. Much of your food processing surfaces are 201 SS."

201 SS is slightly less corrosion resistance than 304 SS, also it may be USDA approved for food grade, I'll have to check to see if its 3A approved for food grade.

My standards book is not readily available to me right now.

(USDA 3A are actually 2 organizations) they work together as well as against each other. ...... bureaucracy.

Inspectors that inspect equipment for manufacturing dairy foods they use 3A standards and what 3A does'nt cover they use USDA standards. While my experience California USDA 3A inspectors tends to use FDA standards at least the inspector I dealt with.

The choice of materials is completely and always decided by your end user.Never should you substitute any other spec, material, or change what the customer specifies.304 SS is used, but never use 304SS if the job calls for 316SS.Also 316SS has a higher nickel content and is higher quality SS.

SS 316 is superior to 304 and 304 can not replace 316. 316 is better in severe service conditions. Their chem composition is also different.

HI All

I Really Agree With you.I am Really Dealing With Valves & Fittings.SS 316 is better in different Services.It is Preferred in RO Systems.I Mean in Water Treatment Systems.Moreover SS 316 can hold till 290 bar but its problem is that it corrodes.

Thanks

Dania MJ

SS 316 contains Cr - 19 % Ni -13 % Mo - 2.5 % compared to SS 304 which has Cr - 18 % & Ni - 8 %. ( on average). The addition of Mo in 316 gives good creep resistance at high (elevated) temperature service compared to 304 type material. Apart from it the corrosion factor is also to be looked into.

Hence designer would have specified taking all these aspects into consideration while specifying the material usage. Please check and change the material if it is not a factor in your applications.

SRIDHAR.

I have some what must be 304 ss fittings on my mast and they started corroding afer 3-4 months. Now after a year and a half they look pretty terrible. I will be replacing them with 316 ss the next time I unstep my mast. I would hesitate trying to sell your customer on metals that are so likely to exhibit surface corrosion. It'll make your job look like crap.

Is your boat on salt water? Is the stainless steel pieces in contact with any mild steel, like bolts or fitting associated with block and tackle? Mild steel in contact with stainless steel will cause the stainless steel to corrode. You can also reduce the corrosion by keeping the stainless steel shined.

Even though the stainless steel is 304, depending on where it was manufactured, can have other impurities still in the metal.

We use stainless steel and mild steel. We have to keep the grinding wheels used on the mild steel separate from those used on stainless because if you use them on stainless it will cause the stainless to rust. Sometimes you can find streaks of rust in new stainless because it was bought from someplace that produces inferior grade of stainless.

You can also compare by using a magnet. Some 304 is magnetic enough to hold a magnet to it. Whereas some 304 doesn't.

Even mild steel submerged in saltwater can have any corrosion almost eliminated by having a piece of magnesium attached to it. Magnesium will pull the corroding properties in the water to it and away from the mild steel.

Thanks for the comments. It's not immersed in saltwater, being on the mast or if it was immersed in salt water being on my mast corrosion would be the least of my problems. Like you mentioned...severe polishing I was advised, then to flush with nitric acid to clean any impurities off the surface.

You might instead want to consider Monel (nickel-copper alloy) instead of 316 SS for your mast fittings. It will be MUCH more expensive, given the cost of nickel these days, but it will be even less prone to corrosion than 316.

The designer has to be consulted before a decision is made to change the material of some part.

Regarding the specific subject of changing ss304 to ss 316:

One of the main differences between them is that (Mo) is added to the ss316, which increases the pitting resistance & reserves the strengh at high operating temperatures.

Hi,

To my understanding, SS 304 and SS316 are stainless steel of different grades, you can find their properties under Wikipedia Encyclopedia website(http://en.wikipedia.org/wiki/Main_Page), this website will show you the differences. I do not know how the grade will affect your application. Another thing is the cost difference, if I remember correctly, SS316 is more expensive than SS304 due to its better properties than SS304.

Yes they are different grades.

If the application is using 316 in the first place there is probably a reason for it because cost would have had them decide on 304 if it wasn't.

Nickel is the cost driver for stainless steel.

You might think that 416 is a better grade then 316 but it's not. 416 ss has mild steel sandwiched between and has a mirror finish.

201 has way less nickel and is more stable in price and has the same handling properties and corrosion reistance as 304 and has a higher tensil strength then 304 and is being given serious consideration as a replacement for 304.

So if you're considering using 304 as an alternate for 316 you might as well look into 201.

We're talking about replacing a component for an oil processing plant.

What's the corrosion properties that are present in this environment. Someone stated that the heat factor might be what's the determinant. Where I work we use a lot of 304 and we also deal with products with a high acidic content.

I don't know what factors come into play when you determine between 304 or 316, so I would ask that of the company and let them determine if 304 would be a reasonalbe alternative to 316.

If 316 is in the scope of the contract then switching to 304 would be a factor in renegotiating the contract.

If denying SS access to oxygen causes a breakdown in the natural protective oxide layer of SS then what happens when you put antifouling paint on underwater SS surfaces like the propeller shaft or in some cases a SS prop? Doesn't that deny access to oxygen? Will corrosion occur under the paint?

If only talk about corrosion under the paint? The answer is yes, it happened as the air with some moisture trapped underneath the paint coating applied and especially the surface are not really taking care off prior painting after blasting. it is often noticed that blister occur after sometime of services and due to the changes of weather and temperature and the chemical reaction.

Painting stainless steel requires that the surface of the stainless steel be roughed up. In a wet environment like that which a boat is exposed it is best to primer the surface.

Since you're painting the surface you really don't need stainless steel. Mild steel is fine since paint is your preservative. You could take the peices that get painted and send them out to be powdercoated. Powdercoating costs fifty cents a pound. Powdercoating is much more durable then painting. This includes epoxy type paints as well.