Time limit b/w welding & hydrotest

[Mahmood Alhinai]

Dear expert,

Kindly what is minimum time limit between completion of welding and the hydrotest?

Thanks

Mahmood

[rehan khan]

No such relationship I read.

Thanks 

Sent from my iPhone

On 19 Jan 2026, at 6:50 PM, Mahmood Alhinai <mahmood....@gmail.com> wrote:



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[venkateswara reddy Desireddy]

Hydrogen cracking will take time like 24 to 48hr. So generally after welding 1 or 2days gap is preferable for hydro test.

To view this discussion visit https://groups.google.com/d/msgid/materials-welding/F3C0BD41-84EE-4868-99B1-9FE16073BB59%40yahoo.co.in.

[indirajith Soundararajan]

Hi

    Immediately you can do hydro if no NDT coverage

Thanks

Regards 

S.Indirajith

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[MADHUSOODHANAN NAIR .G]

  Once the welded joint has cooled and radiographic testing (RT) is accepted, hydrotesting may proceed. Except in cases involving special alloys or stress relieving (SR), a waiting period is required.”  

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[james gerald]

There is no time limit after completion of welding and hydrotest.

Normally after welding the pressure joints, you need to perform NDT and some code specify the time limits between welding completion & NDT& also you perform structural attachments etc..

Thanks & Regards

J.Gerald Jayakumar

0091-8838619635

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[Deerendra Karanth]

The minimum time limit between welding completion and hydro-test is not fixed and ultimately depends upon the specific service content, material type, and the relevant code requirements. These factors dictate the need for any delays for processes like cooling, NDT, or stress relieving before the hydro-test can proceed.

To view this discussion visit https://groups.google.com/d/msgid/materials-welding/2118882983.1252752.1768897077018%40mail.yahoo.com.

[Michel Antony]

Hi,

Hydrostatic test should be preferred only after the risk period for HICC has reasonably passed and all inspections are accepted.

Recommended practice (clear answer)

✅ For Carbon Steel / Low-Alloy Steel

Minimum waiting time: 48 hours after completion of welding

Best practice (critical joints / thick sections): 72 hours

Hydrotest only after:

All welding completed

PWHT completed (if applicable)

VT + required NDT (MT/PT/UT/RT) completed and accepted

Delayed MT/PT after 48–72 hrs shows no cracks

👉 Then proceed with hydrotest

Regards,

MJ

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[Sanga Girivardhana Reddy]

Whether aluminium foil is to be installed before applying the insulation materials on stainless steel pipe/equipment surface?

[DOMINIC V.K]

Dear,

It depends on the paint system applied to the surface. Normally, when a CUI-resistant paint system is applied, aluminum foil wrapping is not required before installing the insulation.However, if a polyurethane-based coating system is used, aluminum foil wrapping may be required, subject to project requirements. Therefore, the requirement for aluminum foil should be confirmed by referring to the project specification or consulting with the painting engineering team.

Best regards,
Dominic V

On Thu, 22 Jan 2026 at 21:07, Sanga Girivardhana Reddy <giri...@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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[Sampath Kumar]

Greetings

No. Aluminium foil (or aluminum jacketing) is not installed directly on bare stainless-steel before insulation.

The correct practice is to apply a corrosion barrier / vapor barrier / separation layer first, then insulation, and aluminium foil or jacketing comes on the outside of the insulation—except in specific cases like removable blankets or internal vapor barriers

Sampath

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[nandakumar pandit]

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 <giri...@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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[Anish R Kurup]

Why Aluminium Foil Is Avoided on SS:

Risk of galvanic corrosion

Traps moisture → increases CUI risk

Not recommended by most standards (e.g., NACE SP0198, ASTM, refinery practices)

Recommended Good Practice:

Clean SS surface

Apply approved primer or barrier coating if specified

Install insulation

Apply aluminium cladding as outer weather protection

Follow project specification and service conditions

With Regards
Anish R Kurup

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[Sampath Kumar]

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

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