clients reject 304 ... 316 must be used, advice needed. 6

[ITownsend]

Hi, I'm hoping that a few of you can provide some insight to why many middle-eastern clients reject the use of 304 (304L etc.) of stainless steel on their sites.
I've witnessed this on a few jobs recently and the only explanation given is that, "in marine atmospheres, 304 is prone to pitting and stress corrosion cracks".

A few questions for thought:
Is this really a massive issue for cold (ethylene) service?
Is the upgrade to 316 a large cost worth undertaking?
Is there any preventative measures against marine environmental corrosion/cracking for 304 over 316 (i.e. fresh water washing/drying, painting etc.)?
Has anyone here successfully pushed through 304 to clients with such demands, where it was clearly the correct material choice?

I hope you can provide a little insight into this...

Many Thanks
IT

 

[stanweld]

Desert marine environments are very severe from a corrosion standpoint. 304 SS has has a historically poor performance (corrosion resistance) record in these environments.

 

[EdStainless]

In many plants the external corrosion risks are worse than the process side issues.
The SCC risk comes about because the process is hot enough to exceed the critical temperatures. But in this case 304 and 316 are virtually identical.

Actually 316 is a huge waste. If the process runs under 600F then these should be built in a lean duplex (2101, 2102, 2003).
You would get pitting resistance at least equal to 316.
They are stronger so you could use less metal.
The SCC resistance is an order of magnitude better than 316.

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Plymouth Tube

 

[blacksmith37]

I would say you are pushing on a rope; The client wants 316, sell him 316.
And, in a cold service ,marine environment (water condensing), 304 would look bad quickly. For specofic corrosion rates there is a lot of data from Kure Beach, published by Inco/ Huntington decades ago. NiDevelopement may still make data available.

 

[mcguire]

I just specified Allegheny's 2003 duplex for a airport roof in Qatar because 316 was inadequate, let alone 304. The Mideast has the world's toughest environment.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[davefitz]

a good comparison of the relative corrosion resistance of modern duplex and SS can be obtained for free from Outokumpu at :

<//

http://www.outokumpu.com/About-us/Business-news/News/Latest/Outokumpu-Stainless-Corrosion-Handbook/>

 

[ITownsend]

Thanks for all of your contributions,
Does anyone have any experience with painting of 304 or 316 for external corrosion issues to mitigate (marine) environmental corrosion? Even if this involves painting a vessel which may be under insulation in service.

I would tend to look towards the suggestion of EdStainless and specify duplex stainless to save costs and reduce vessel/exchanger weights. The issue is that, as blacksmith37 states: Clients always request 316 stainless and changing their mind is very difficult. Even if there are more corrosion resistant or cheaper/lighter materials available, the client won't be deterred.

 

[davefitz]

If the client specifies 316 SS, he has already accepted all liability for corrosion. If you substitute another alloy selection, you are now adopting some or all of the corrosion liabilities.

Also, there are some tricks to using duplex alloys -if you have no experience with the specific duplex in the same application, you will find its not just a simple selection change- design and fabrication details need to be addressed to avoid unintended consequences in the field. Some duplexes may have excellent "general corrosion" characteristics if fabricated and welded to the correct crystal structure and with proper weld "overmatching", but have serious issues with either crevice corrosion or MIC microbiological induced corrosion, as found at coal fired plant WFGD piping. And the assumption of correct crystal structure and weld detail ( espescially on thin components) cannot be taken for granted.

 

[EdStainless]

dave, The duplex issues in FGD are where they were used in place of 6%Mo alloys. This was a big step down and a real risk.

External painting of piping systems is a real pain. It needs to be done in a shop and well inspected. A two coat epoxy is the most common. Then they field patch the welded joints.
I doubt that you can get them to change their mind this time but you might want to put together a package and try to get them thinking this way.
You have three good alloy options, ATI2102, LDX2101, DX2202.
Good luck.

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Plymouth Tube

 

[salmon2]

thank you davefitz. that is a good deal, free book.