Verified gap of socket weld?

Why we need to verify the gap of socket weld?

To permit the thermal expansion of pipe during welding operation.


Thanks and one more questions:

  1. Max. and Min. in mm are allowed?
  2. Which NDT method application to check the gap?

Generally 1.5mm before welding & i dont know in depth.
RT is used for measuring the gap after welding.


Only shot a film to verify the gap, no IQI selection, right?
In this case, we also review the throat thickness of fillet weld.


1/16" before welding (aprox) and what should be done in case after RT “no gap” is verified.
Is it acceptable, It is not, Why?

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Its depends.
The reason behind this gap is to avoid unwanted shear stress in the fillet and possible cracking during operation, especially those high-temperature service when pipe inside the socket will expand to a greater degree than the socket itself.

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I know that, this was not my question.
What should be done in case after RT “no gap” is verified.
Is it acceptable, it is not? Why.

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I consider on fatige cracking during operation due to thermal expansion.


in my opinion, check the gap and throat thickness of fillet weld.
In case of RT films did not find the the gap, it should repair.

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Please share the common acceptance criteria?

Hi @Aravind_km and @dinhhoan05
Any advice for this.

IF you verify the Gap by VT , RT is mandatory?

If visual inspection found the gap, there are no reasion to verify RT film.
But in case of conner joints such elbow, Tee, pipe to valve.

So, following specification are mandatory.

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definitely it is rejected and need to repair