Dear experts greetings
1. Why this question is important (Stainless Steel + Insulation)
Stainless steel equipment and piping are highly susceptible to:
Chloride Stress Corrosion Cracking (CSCC)
Crevice corrosion
Corrosion Under Insulation (CUI)
Direct contact of aluminium foil or wet insulation with stainless steel can trap moisture and chlorides, leading to premature failure.
2. Correct Insulation Layer Arrangement (Standard Practice)
Typical Correct Layer Sequence
Stainless steel surface
Surface preparation + protective coating / corrosion barrier
Insulation material
Aluminium foil / aluminium cladding (weather & mechanical protection)
3. Is aluminium foil installed before insulation?
General Answer: NO
Aluminium Foil Allowed?
Reason
Directly on SS pipe
Not recommended
Risk of moisture trapping & CSCC
As insulation facing (factory laminated)
Yes (with conditions)
Acts as vapor barrier
Over insulation (outer jacketing)
Yes
Weather & mechanical protection
Removable insulation blankets
Conditional
Must have SS mesh + barrier
4. What should be applied on SS surface before insulation?
Mandatory for Stainless Steel (per standards):
Surface Preparation
SSPC-SP1 / SP2 (cleaning)
Remove grease, oil, chlorides
Corrosion Protection / Barrier
High-temperature epoxy
Silicone aluminum coating
Thermal spray aluminum (TSA) for severe services
Separation Layer (very important)
Glass cloth
PTFE sheet
Chloride-free barrier tape
This prevents direct contact between insulation and stainless steel
5. Role of Aluminium Foil in Insulation Systems
Aluminium Foil is used for:
Vapor barrier (cold insulation)
Reflective heat barrier
Protection against moisture ingress
But only in these positions:
Laminated to insulation (factory applied)
Outside insulation as jacketing
6. Special Case: Cold Insulation (Cryogenic / Sub-ambient)
Layering Example:
Copy code
SS pipe
Anti-corrosion coating
Vapor stop / mastic
Insulation (PIR / PU / Foam glass)
Aluminium foil facing
Aluminium cladding
Here, aluminium foil works as a vapor barrier, not a direct SS contact layer.
7. International Standards & Specifications
Relevant Standards
ASTM C795
Specification for insulation materials in contact with stainless steel
Limits water-soluble chlorides
ASTM C692
Test method for CSCC of stainless steel under insulation
NACE SP0198
Control of Corrosion Under Insulation (CUI)
API RP 583
Best practices for CUI management
ISO 15665
Acoustic & thermal insulation of piping
Shell DEP / Saudi Aramco SAES / ExxonMobil specs
Explicitly prohibit bare aluminium foil contact with SS
8. Best Industry Recommendation (Oil & Gas / Power / Chemical)
DO
Apply protective coating on SS
Use chloride-free insulation
Use aluminium foil only as facing or jacketing
Seal all joints to avoid water ingress
DON'T
Wrap aluminium foil directly on SS
Allow insulation to touch bare stainless steel
Ignore vapor barriers in cold service
9. Final Conclusion
Aluminium foil should NOT be installed directly on stainless steel before insulation.
The correct procedure is: SS surface → protective coating / barrier → insulation → aluminium foil/jacketing.
With best regards
Sampath
On Fri, Jan 23, 2026, 7:00 PM Anish R Kurup <anishkrp4@gmail.com> wrote:
Why Aluminium Foil Is Avoided on SS:Risk of galvanic corrosionTraps moisture → increases CUI riskNot recommended by most standards (e.g., NACE SP0198, ASTM, refinery practices)Recommended Good Practice:Clean SS surfaceApply approved primer or barrier coating if specifiedInstall insulationApply aluminium cladding as outer weather protectionFollow project specification and service conditionsWith Regards
Anish R Kurup--On Fri, 23 Jan, 2026, 6:43 pm nandakumar pandit, <panditns1@gmail.com> wrote:Yes,this is to prevent corrosion of the SS surface by chlorides present in insulation material as the aluminium works as sacrificial material.--On Thu, Jan 22, 2026 at 10:37 PM Sanga Girivardhana Reddy <girisanga@gmail.com> wrote:Whether aluminium foil is to be installed before applying the insulation materials on stainless steel pipe/equipment surface?--
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