Stainless steel austenitic grades are susceptible to stress corrosion
cracking because of their Ni% content (range between 10 - 30%). You
should substitute the 304 for a duplex grade (like 2205) or a nickel
alloy, following recommendations of Mrs. Bagchi.
The presence of Cl / F (a few mg / l) will increase the probability of
pitting corrosion mech; These mechanisms (pitting and scc) acting
together represent a very severe operating condition. Molybdenum
alloys have best pitting resistance (eg.: 316L has 2-3% Mo and its
PREN ranges 24 versus 18 of 304).
A think you should check the presence of halogens again.
Note: PREN - Pitting resistance equivalent number (higher is better).
On Dec 21, 3:09 am, snbag...@aol.in wrote:
> Dear
> ENG. Ryiad Alzoubi
> A simpler and cost effective solution could be to electro-plate or (better) clad the inside surface of the bellows with nickel or clad with Monel/Inconel type corrosion resistant alloys. For more options and details, you can contact me at snbag...@ymail.com.
>
> Regards,
> S.N.Bagchi.
>
> -----Original Message-----
> From: Tirumala B N Tagore <tagore....@gmail.com>
> To: materials-welding@googlegroups.com
> Sent: Sun, 20 Dec 2009 11:26 pm
> Subject: Re: [MW:3856] Stress Corrosion Cracking in expansion joints
>
> 1.Expansion joints lateral deflections are to be verified whether they are in range. Axial expansions are normally catered. Lateral deflections do have confined limitations.
> In the first stage you need to examine at least one expansion joint for metallurgical evaluation.
>
> 2.since the failure is noticed from inside to outside, please look in to steam being handled (inside fluid) whether it has some traces of Chloride as well as sulphur compounds.
>
> 3.Normally expansion joints can have some condensates collected during turn arounds and / or during some process upsets and this collected condensate , if with chloride / sulphide , then you have this problem . However you can suspect this if failure is at bottom portion on horizontal lines.If this is the case, you may mitigate the next failure if drain connections are provided.
>
> 4. SS duplex or Incoloy Expansion bellows to be choosen , when you can replace in stages. for duplex, you MUST establish that the root cause is stress corrosion cracking only.
> Tagore
>
> On Sun, Dec 20, 2009 at 4:45 AM, rzoubi <rzo...@just.edu.jo> wrote:
>
> Dear Forum Members,
>
> We have consructed a high temperature hot water disrict heating system early in the year 2000,the initial insallation of the system was not so good -there were some axial and lateral deflection in the system- .The expansion joints are made fromS.S304,after 3 to 4 years of operation ,we noticed cracks in the bellows ,starting from inside to outside the layers(9 layers).When refering this prblem to some experts in our country, they called it stress corrosion cracking related to chloride content in the sarrounding envr..W e asked an expert to ckeck the presence of chloride in the envr., he found no traces of this gas.As we have no budget to replace all the expansion joints in the future,we are obliged to replace the defected exp.joint when the joint starts to leak.In order to vercome this problem we are thinking to paint these joints with a high temp. resisiting paint up to 200degree c,as the max.operating temp. is 150degree.(the operating pressure is around 20 bar).
> Plase advise whether this idea is right,if not please give us another solution.
>
> Thank you in advance
> ENG.RIYAD ALZOUBI
>
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