Re: [MW:36089] Request for Technical Opinion – Leakage in SS 316L Schedule 10S Line After 4 Months of Service
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
Website: www.aesinspections.in,
Email: info@aesinspections.in
Associated Engineering Services
#3-5-944/205-206 & 220-221,
2nd Floor, Panchavati Mall,
Narayanaguda, Hyderabad, India.
Mob.No: +91 9032585485
Website: www.aesinspections.in,
Email: info@aesinspections.in
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On Friday, June 26, 2026 at 01:13:46 PM GMT+5:30, 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:
- Weld joints
- 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
https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
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