RE: MIC on Potable Water Piping.

From: <Ahmed>
Date: Tue May 29 2001 - 07:27:00 EDT

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: <a href="/group/PipingDesign/post?postID=KiZdZ_WxZaioZ6KgM8pQcCGrfZOkiHYhowx6k_TLZOfvpPDJASjonZH0nIt3WZIcvQDGT4duI-4pvIfSutkNfY8B">PipingDesign@yahoogroups.com</a> 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 Tue May 29 07:27:00 2001