Before commissioning, do you do chemical cleaning on the pipelines to remove the annealing color from the HAZ area???............. Maybe around the HAZ area, there are a lot of oxidize carbon which can affected the corrosion resistance of the stainless steel.
> Ahmed
> er-308L tig welding used on 300 joints - butt weld. the whole works
related
> to NDE was observed. attack was observed only at the bottom ( 6 oclock)
all
> withihn the HAZ. schedule 40S pipe. not only was TDS and pH check, but an
> EDS exam of the residue was also performed by Nalco.Main consitutents on
the
> pits is carbon,hence the microbes. To quote nalco " the most likely cause
> for this perforation is microbiologically influenced corrosion involving
> acid producing bacteria". sample of the potable water indicated a 15 ppm
> choloride.
>
> we are near the red sea which is considered severe environment. Outside of
> pipe looks OK. failure initiated form the inside. i must add that it took
> perhaps 2-3 weeks before the hydro test water was drain. layup procedure
was
> not observed during this particular period.
>
> -----Original Message-----
> From: Ahmed Vawda [mailto:avawda@aksugar.co.ae]
> Sent: 29 May, 2001 2:28 PM
> To: 'PipingDesign@yahoogroups.com'
> Subject: RE: [PipingDesign] MIC on Potable Water Piping.
>
>
> Ralph
>
> Firstly, I assume that you have considered and buried the possibility of
any
> galvanic corrosion between the weld material and the SS304?
>
> This is the first microbe that I have heard of that can withstand a shock
> dose of chlorine. Chlorine, being an oxidising biocide is usually
recognised
> to kill all known microbes, given a minimum concentration of about 2 ppm.
> Perhaps the time and exposure of the microbe to Chlorine is too short.
> Some anaerobic bacteria are known to produce slime or cysts and hide
behind
> these. The trick in aseptic piping is to ensure no crevices exist in the
> first place, which is where these bugs will first squat.
>
> Chlorine on the other hand, is also well known to cause stress corrosion
in
> stainless steel, SS304 included. So I wouldn't rule chloride induced
> corrosion just yet. Why only at the weld? Maybe its the weakest link in
the
> corrosion chain, or is galvanically assisted.
>
> What is the thickness of the welded butt and pipe thickness.
> What is the colour of the affected joints?
> What is the recorded TDS, temp and pH of this water?
> What is the water source, ground, surface, desalinated?
> Has the lab given a name to these bugs?
>
> Perhaps if the water is aerated, these bugs will just die.
>
> Regards
> Ahmed Vawda
> Process Engineer
> Al Khaleej Sugar
> Dubai
>
> -----Original Message-----
> From: SARE, RALPH H. [mailto:SARERH@YANPET.SABIC.com]
> Sent: Tuesday, May 29, 2001 3:03 PM
> To: PipingDesign@yahoogroups.com
> Subject: [PipingDesign] MIC on Potable Water Piping.
>
>
> Contractor has just completed the installion of 6" 304L ss potable water
> piping. After 3 months, 50% of the 300 welding joints has been observed
> leaking . Pitting attack has so far been confined only at the weld
joints..
> No failure was observed in the process ss lines.
>
> Expert from Nalco has been called to assist and identify the cause of
> pitting and weld failure. Nalco says the cause is MIC. No it does not
stand
> for microphone but rather to microbiologically influenced corrosion caused
> by anaerobic acid producing bacteria.
>
> System has been treated with shock dosage of chlorine, but what do you
know.
> Damn MIC can survive in chlorinated water. Its source unknown.
>
> What suprises us is how come this bugger only loves to eat a weld joint ?
> Our lab has also indincated that this bacteria is no health hazard -
system
> is potable water. Meaning its ok to drink the wtaer because the MIC only
> attacks a ss weld joint (the bugger must have hated a human intestine)?
>
> Anybody has any experience on this MIC?
>
> Metallurgist suggestion is top apply a leeve around the weld joint using
> AL-6XN or wrap with fiberglass or compeltely replaced it with galvainzed
cs
> pipe.
>
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Received on Wed May 30 08:04:00 2001
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