Request for Technical Opinion – Leakage in SS 316L Schedule 10S Line After 4 Months of Service

[Karuppa Samy]

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

[Bhavani Prasad Emani]

Hi Karupa samy,

Yes — the pattern you described strongly suggests a post-hydrotest localized corrosion problem rather than a simple pressure-test failure, especially because the line held during hydrotest and leaked only after months in service.

Most likely reasons

Residual hydrotest water left inside the line. Stainless steel systems can fail weeks or months later if test water is not fully drained and dried, especially in low points, dead legs, and crevices.

Chloride pitting / crevice corrosion. Chlorides in hydrotest water, cleaning water, or trapped contamination can break down the passive film and create pinhole leaks, often first seen at welds and local stagnation points.

MIC after stagnant water retention. If untreated/raw water remained trapped after hydrotest and the line sat idle before/after commissioning, microbiologically influenced corrosion can produce pitting and leakage within weeks to months.

Weld-affected zones are more vulnerable. Weld toes, heat-affected zones, root side defects, heat tint, and incomplete post-weld cleaning/pickling are common initiation sites for pitting and SCC.

Stress corrosion cracking, if temperature/chlorides/stress were unfavorable. Austenitic stainless steels can crack under tensile stress in chloride-containing environments, with weld residual stress making joints especially susceptible.

Fabrication defects exposed later in service. Small lack of fusion, porosity, undercut, or incomplete penetration may survive hydrotest but open up after thermal cycling, vibration, or pressure cycling during operation.

Thanking you,

With best regards,                                            

           

Bhavani Prasad Emani,
Associated Engineering Services
#3-5-944/205-206 & 220-221,
2nd Floor, Panchavati Mall,
Narayanaguda, Hyderabad, India.
Mob.No: +91 9032585485
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[Jenish Mistry]

Hi Krupa ,

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

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[vishal Bhansali Metals]

The Primary Cause for failure shall be Chloride-Induced Stress Corrosion Cracking (SCC).

Contributing Factors:

  - Post-Hydrotest Preservation: Evidence suggests improper or missing preservation procedures following the hydrotest.
  - Weld Integrity: Residual stresses remaining in the welds.
  - Contamination: Likely chloride contamination during or after testing.

Required Preventive Measures:

  - Water Quality: Utilize low-chloride hydrotest water, ideally maintaining levels <50 ppm Cl⁻.
  - Post-Test Protocol: Ensure immediate draining followed by thorough drying using air blowing or nitrogen.
  - Surface Treatment: Apply a formal passivation treatment and ensure all weld heat tint is removed via pickling and passivation.
  - Material Specifications: Evaluate the use of SCC-resistant materials, such as Duplex SS, for critical service components.
  - Documentation: Maintain strict preservation records for all future assets.

Regards,

 

Sushil Bhansali – (+91) – 9082159270 / 9870846831

Pioneer Steel And Engineering

Mumbai,India

Email:vis...@bhansalimetals.com

Web: www.wirestainless.com

[Karuppa Samy]

Dear Jenish Mistry,

Utility water service

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K. Karuppasamy

[Muhammed Sharafudeen.C.H.]

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

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[sridhar cn]

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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[Karuppa Samy]

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

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K. Karuppasamy

[Marco Nunes]

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

M Nunes

Senior Materials Engineer 

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[Muhammed Sharafudeen.C.H.]

Dear all,

Kindly advise on the appropriate repair method for the corroded pipe spools.

Specifically, please confirm whether the following repair options are acceptable:

Can the corroded bottom portion of the pipe spool be cut out and replaced with a new section of the same material, using the approved WPS and qualified welding procedure?

Alternatively, is it acceptable to insert a pipe of the same diameter inside the corroded section and perform internal fillet welds as a repair method?

As I am not a welding specialist, I would appreciate your technical guidance on the most suitable repair approach. Please also provide a detailed repair procedure, including inspection and testing requirements, so that the repaired spool can be accepted and handed over to the client.

Since this project is located at a major airport, the repair method must comply with the international procedures, and relevant codes and standards.

Warm Regards...

Mohamed Sharafudeen C.H

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[sridhar cn]

 Dear Mr. Sharafudden,

You have not mentioned the type of material used, its thickness, application, Standards followed and other details. 

In our view, repair should comply with internationally accepted practices such as ASME B31.3 (Process Piping).

Cut out the defective portion and replace it with a new pipe. Inserting a new pipe within the existing pipe and

fillet welding is not a good idea, as it may create stress concentration. Also, cannot be accepted as a permanent 

repair process under the code. Hence,

• a.   Identify and mark the defective areas by VT, and UT (if possible) for pipe thickness measurement.

b.  If pitting extends beyond the visible leak, extend the cut until only unaffected material remains.

c.  Fabricate a new replacement section after PMI, and use a suitable welding process.

d.  Prepare a repair WPS, and make sure that the weld meets the WPS norms and the welder is qualified. If it is SS, 

     maintain  the interpass temp. and strictly control the heat input. Perform100% VT and RT.

e.  Have a check on the hydor-test water for its chemistry, Chloride, Sulphur, iron content, and pH factor before using it.

f.  Post hydro test, drain all the standing water fully with dry (oil free) compressed air.

g. Complete the weld map, weld records including, base and filler materials. batch certificates, fit up, weld and NDT 

    report, pressure test etc. 

h. Make sure that everything is in order.

Trust above info. will be of help to you to make a start to repair the defects and overcome the issues.

C Sridhar.

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[Mohd Siraj]

1. DSS and SS lines are susceptible to SSC and chloride pitting.

2. After hydrotesting with DM water, maintain a nitrogen atmosphere if the line will not be used.

3. Perform adequate pickling and passivation.

4. Review MOC compatibility, chemical treatment, corrosion risks, and monitoring measures.

[nagendran natarajan]

Dear Mr.Karuppa samy  ,

Pls share us the Reports so that everyone will be enlightened..

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With Regards

Nagendran Natarajan