Porosity Acceptance Criteria

[Ripz]

Using ASME B31.3 as a reference; why is surface porosity always unacceptable regardless of size, while internal porosity has an acceptance criteria.

Let's assume both are the same size, why does the fact that it's on the surface make it unacceptable?

 

[DekDee]

Ripz,
Have a look at Table 341.3.2 Note 5,
Regards,
DD

 

[Ripz]

DekDee, I saw this note but it confuses me even more.

(5) These imperfections are evaluated only for welds ≤ 5 mm (3⁄16 in.) in nominal thickness.

I assume it means that for welds below 5mm thick are evaluated. But for welds thicker than 5mm are not evaluated? Does that mean all surface porosity is acceptable or not?

 

[EdStainless]

What I was always told was that you removed surface porosity, and if you still met the thickness criteria then you were fine.

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Plymouth Tube

 

[metengr]

Because surface porosity can result in lower fatigue properties since stresses are highest at a free surface. Also, surface porosity will interfere with surface NDT interpretation.

 

[weldstan]

Surface porosity is acceptable for T > 5mm under B31.3. Whether it should be acceptable is a matter for the Owner to include in its specifications. Porosity in thin welds may reduce the supporting ligament to such an extent where in service leakage could occur and there is plenty of emperical evidence to support such failure. As T increases, the deleterious effect of porosity on the strength of the material to resist leakage during service greatly deminishes. No surface porosity is permitted for High Pressure Piping (K pipe)

 

[Ripz]

Weldstan:

You said "Porosity in thin welds may reduce the supporting ligament to such an extent where in service leakage could occur and there is plenty of emperical evidence to support such failure. "

But this condition would occur for both internal and external porosity. it doesn't give me a reason which explains the difference in acceptability.

metengr,

"Because surface porosity can result in lower fatigue properties since stresses are highest at a free surface"
You said "it can", tehn that to be should have allowed some to be acceptable and then you should have an acceptance criteria?

 

[Ripz]

metengr,

"Because surface porosity can result in lower fatigue properties since stresses are highest at a free surface"

You said "it can", then some sized porosity on some thickness weld should have allowed some to be acceptable and then you should have an acceptance criteria?

 

[Ripz]

Let's say, for example, we have a 2 mm diameter pore, with a visible depth of 1 mm. How can ASME now give a blanket statement that ALL surface porosity is unacceptable? Now the contractor will have to repair this innocuous pore, because of this.

I don't agree that porosity can obscure the interpretation of surface NDT, as a trained NDT Professional's job is to interpret discontinuities.

 

[weldstan]

Ripz,
Review comments regarding fatigue and corrosion (add corrosion fatigue) at surfaces (internal or external) exposed to corrodants.

 

[metengr]

Ripz;

You said "it can", tehn that to be should have allowed some to be acceptable and then you should have an acceptance criteria?

.

Reply; No.

Here is a tip, if you have a problem/issue/concern with the code, either attend a code meeting and voice your concern or more important submit an inquiry.