Re: [MW:36096] Request for Technical Opinion – Leakage in SS 316L Schedule 10S Line After 4 Months of Service

I agree with the MIC process as the main failure mechanism. 

M Nunes

Senior Materials Engineer 

On Sat, 27 Jun 2026, 3:19 am Karuppa Samy, <samyqc08@gmail.com> wrote:

Dear Sridhar,

Thank you for your kind response and valuable inputs on this matter. We are currently analyzing the root cause of the issue, and your insights will be highly beneficial to our efforts. We truly appreciate the time you have taken to share your thoughts with us.

Thank you once again for your support.

Regards,

K. Karuppasamy

On Fri, Jun 26, 2026 at 9:39 PM sridhar cn <sridharcn305@gmail.com> wrote:

Dear Mr. Karuppasamy.

Please refer to the issues you have faced in your SS 316L pipes both on the weld joints and base pipe.

Since the media is 'utility water', and the leakage occurred after 4 months in service, the probable 

causes could be:

1.  Hydro test / Utility water:

a.  Stagnant hydrotest water / poor preservation, Utility water is often left idle for periods during commissioning. 

b.  If hydrotest water was not completely drained and dried, dissolved oxygen promotes localized corrosion or

     water evaporation concentrates Chlorides.

c.  Pitting initiates beneath deposits or in crevices. Thin schedule 10S pipe can be perforated relatively quickly. 

    This mechanism can affect both welds and parent metal.

2. Microbiologically Influenced Corrosion (MIC):

a.  Utility water is particularly susceptible to MIC if the system remains stagnant.   

b.  The pre-water treatment was not started promptly.

c.  MIC often produces small pinholes and deep pits leading to localised leaks.

c.  A leak after only a few months is entirely consistent with aggressive MIC under its own favorable conditions.

3. Pitting Corrosion due to Chlorides:

a.  Although 316L has good corrosion resistance, it is not immune to high chloride content in utility water.

b.  Deposits on the internal surface and Crevices create oxygen concentration cells.

d.  Since the pipe is thin, even localized pitting can penetrate the pipe within months.

4. Chloride Stress Corrosion Cracking:

a. SCC usually requires, Tensile stress and Chlorides, 

b. If your utility water operates near ambient temperature, SCC becomes less likely.

   If chloride levels are high and residual welding stresses are significant  SCC becomes more likely.

Please check the source of the utility water. Is it a bore, river or treated water? Also check the chloride 

concentration (ppm) in the water used. Was the line completely drained and fully air-blown? These are 

some of the important steps to be considered prior to and after the hydro test.

5. Suggestions:

Please remove one leaking pipe section, including the weld and perform visual examination / PT of both 

internal and external surfaces.

Perform metallographic examination of the leak (weld & pipe) areas.

Further analyze the utility water for Chlorides, dissolved Oxygen, pH factor, and sulphates.

If possible, inspect the internal surface using a borescope to determine whether damage is widespread or localized.

In a nutshell, the reasons could be due to: 

1. Improper post-hydrotest preservation leading to localized corrosion,

2. Microbiologically Influenced Corrosion (MIC),

3. Pitting corrosion due to chlorides in utility water,     (or)

4. Localized corrosion in the crevices or Chloride Stress Corrosion Cracking.

Hope the above info. will help you to analyse and take suitable remedial action.

C Sridhar.

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On Fri, 26 Jun 2026 at 17:24, Muhammed Sharafudeen.C.H. <sharafu.nooru@gmail.com> wrote:

Dear all,

We have similar case in our project where the stagnant water cause 316l fire water utility lines spools inside valve chamber due to MIC. Anyone suggestions how to repair this?

Since these are corroded at bottom portion of SS316l 6" , 12" and 24" buried lines. 

Much appreciated .

Warm Regards...

Mohamed Sharafudeen C.H

On Fri, Jun 26, 2026, 1:52 PM Karuppa Samy <samyqc08@gmail.com> wrote:

Dear Jenish Mistry,

Utility water service

On Fri, Jun 26, 2026 at 2:04 PM Jenish Mistry <jenishmistry1992@gmail.com> wrote:

Hi Krupa ,

Can you share further information regarding which service, the line had been in use for 4 month period ?

On Fri, Jun 26, 2026 at 1:13 PM Karuppa Samy <samyqc08@gmail.com> wrote:

Dear All,

We would appreciate your technical opinion regarding a leakage issue observed in stainless steel piping after several months of operation.

Background:

• Line sizes: 2" and 6" 361L Stainless Steel (Schedule 10S)
• NDT coverage: 10% completed as per project requirements
• Hydrostatic test: Successfully passed without any leakage
• Records related to line preservation after reinstatement are not available, as the system was under the control of the Pre-Commissioning and Commissioning teams
• The line has been in service for approximately 4 months

Issue:
Leakage has recently been observed at several locations, including:

1. Weld joints
2. Pipe body/base material

  Considering that the line successfully passed hydrotesting and has been operating for several months before the leakage occurred ,  

 Could you please share your views on the potential reasons

Thank you in advance for your valuable inputs.

Best Regards,
Karuppasamy

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