304 or 316 stainless steel

[Peter]

Looking to get a gantry and a few bits made for the boat. The fabricator I getting prices off has quoted 304 marine grade S/S as its cheaper than 316S/S. My understanding was that for saltwater use you should use 316 S/S. What are the issues in using 304S/S as opposed to 316S/S.

Peter

 

[PCUK]

304 is fine above the water-line.

 

[kieronriley]

not on my boat !316 all the time

 

[jimbaerselman]

Although written for the pharmaceutical industry, you may find this link informative.

 

[maxi77]

I am thinking of having a gantry made, can you give some idea of the costs you have been given.

Thanks

 

[PCUK]

kieron, feel free to waste money!!!

 

[MapisM]

How much cheaper?
I'd expect the finishing alternatives (mirror-like polished/rough/painted) to be more relevant costwise than the raw material as such.
Besides, in applications where some flexibility is required (e.g. coils) 304 is even better than 316.

 

[Graham_Wright]

The price of stainless steel is increasing all the time.

I buy 303, 304 and 316 for my business.

For a non-marine application, I paid £3.95 per metre dated 27 June 2008 for 304 hygenic, welded polished 25mm OD X 1.5 wall.

I have just asked my supplied for a comparison, and like for like, they have quoted £5.93 per metre for 316 and £4.07 for 304. This was for 1" diameter tube which is more readily available than 25mm.

In my book, the material cost is likely to become insignificant compared with the cost of labour.

I would suggest you ask for a competitive quote from DC Welding (01531 640779, Richard) who only use 316 and produce high quality work. (No connection, just a satisfied customer).

 

[chrishelen]

I read somewhere that Stainless should never be used below the waterline because it needs air to keep its special properties.

 

[Graham_Wright]

If his gantry's below the waterline, he's got bigger problems!

 

[npf1]

Got both on my boat. After a transat, many of the stanchion bases in 304 were rust stained (which did polish off but left some pitting), whilst stuff in 316 attached to them was not. Sure, this might also be due to the quality surface finish, but if it were my boat I'd pay the extra. Plus much less polishing required to keep it looking good.

 

[rogerthebodger]

I have made lots of stainless for my boat and only use 316. Yes 304 is cheaper but I don't wont to remake any items a second time !!

 

[timtap]

See ? There's the answer.... Buy the Tig welder,Pipe bender and a few power tools , Get a bucket of stainless offcuts and lock yourself away for a couple of days and learn how to do it yourself..... There is only one problem and thats fighting other people off, co's once you have mastered it you will have a queue of fellow boat owners at the door wanting all manner of additions to their boats.
I bought a cheap welder and for under a couple of hundred pounds and it paid for itself almost immediately.

 

[kieronriley]

as has been stated the price is in the labour the difference between a part made in 316 and 304 is not as significant as some seem to think and in my book buy once(the best) and save on the re purchace ,if thats wasting money then bring it on

 

[Alcyone]

Mate of mine has a stainless steel riser chain on his mooring in West Wales. It has been there for three years now and, although there is a slight staining of rust, it is fine, and weed free. He didn't buy it, you understand, it acquired him.

 

[chrishelen]

/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

 

[tobble]

As others have pointed out 316 is more corrosion resistant, but 304 has (I think) a higher unltimate tensile strength, but more importantly is less prone to work hardening.

If you try putting in a stainless screw with torque control on your power screw driver, you will shear the head off quite easily, especially true of 316.

If you have a lot of weight on the gantry it'll bend a little everytime the boat pitches... having said that I've never heard of anything like that failing.

 

[pyrojames]

Not true I am afraid. 316 has both a higher UTS and YS than 304. It has however a lower strain to failure than 304, which may be taken as a work hardening problem, depending on operation parameters. As long as working loads are kept below 50% YS cyclic failure is extremely unlikely, so in that case, 316 will prove more resistent to higher cyclic loads. However, if you have a situation where the materials cycle is strain limited (rigging is typical) then the 316 will work harden and fail more readily. The process of work hardening is actually where the YS increases with cycles until it appraoches the UTS and then failure occurs.

 

[Graham66]

I have some safety rails manufactured from 304 stainless and it certainly does the job strength wise but not so good on the cosmetic front.
the draw back being that you have to keep it polished otherwise rust staining can occur on the GRP

 

[William_H]

Hi Alcyone.. I now have an almost all stainless steel swing mooring.

It started when we were supplied obligatory buoys for the moorings with SS swivel built in. The ss has been known to fail so the swivel is now bypassed. The iron to SS meant that the iron corroded rapidly.
Later I was given enough stainless steel chain for the riser.
It is of an unknown material but came from inside a furnace.
I connected it with iron shackles and found that the iron disappeared rather rapidly. due to different metals. I have now gone for s/s swivels and shackles and am hoping for a long life from the mooring.

At the bottom there is inevitably a ss to iron shackle join but this is in area where there is little movement and so it seems to be surviving. I have now another lump of SS chain to add at the bottom which will total a huge SS chain to drag if the iron shackle does give way.

It is all still a bit of a worry. There seems to be lots of advice that SS is no good under water but I really think it is all going to last much longer than iron. It is grossly over sized for the boat size.

The main saving grace is that I tend to look at all the mooring very often when snorkelling ie every few weeks so can pick up excess corrosion. So time will tell if it is all a good idea. The first SS chain has been on about 4 years. olewill