Microfissure
Microfissure
(OP)
Good Day!
I am working in a Power Plant and as we have conducted an in-service Borescope inspection in the tube to header connection, some discontinuity was observed. The HRSG was operating for more than 2 years now.
As per our clients report based on the photos taken during the inspection, they have mentioned that there were microfissure on the root weld measuring 0.2mm
The materials are P91, P22, P11
I would like to ask:
1) What causes microfissure?
2) Which reference can I read in order to understand microfissure?
3) How do we measure microfissure and what method or procedure?
Thank you very much.
I am working in a Power Plant and as we have conducted an in-service Borescope inspection in the tube to header connection, some discontinuity was observed. The HRSG was operating for more than 2 years now.
As per our clients report based on the photos taken during the inspection, they have mentioned that there were microfissure on the root weld measuring 0.2mm
The materials are P91, P22, P11
I would like to ask:
1) What causes microfissure?
2) Which reference can I read in order to understand microfissure?
3) How do we measure microfissure and what method or procedure?
Thank you very much.





RE: Microfissure
RE: Microfissure
RE: Microfissure
RE: Microfissure
RE: Microfissure
Material: same material was used, P22, in this particular issue of microfissure.
Operation: base load
Visual indication:on the weld root
With regards to the measurement, they just sent us the report that the microfissure measures 0.2mm but not mentioned how they came up with that measurement.
History:
There has been a contamination of seawater which causes the refurbishment. During the inspection of the headers (using borescope,)it was found that there where lack of root fusion, incomplete penetration, cracks and excess filler cuts.
Due to the discovery of the these flaws/discontinuities, all of the 8 HRSG units where scheduled for tube-to-header borescope inspection.
Sample photo is attached for reference.
As per ASME Section I, there is no mandatory visual inspection for tube-to-header connection and therefore the is no acceptance criteria.
Regards,
AWeld1
RE: Microfissure
RE: Microfissure
How dangerous is these intergranular cracks?
Another information is that these intergranular cracking was also present in the tube-to-header weld in the new harp that will be used as a replacement.
What causes these interganular cracking?
RE: Microfissure
High temp Creep is intergrannular.
RE: Microfissure
Well, at this point corrosion fatigue crack propagation (start-up and shut downs) can drive existing cracks through-wall to produce tube leaks. This will reduce reliability of the HRSG. Are these tube to header weld joints actually full penetration welds?
I agree with weldstan that these cracks probably occurred from environmental-assisted cracking associated with the ingress of seawater.
RE: Microfissure
RE: Microfissure
If you know the stand-off distance on you fiber scope you can calibrate the image magnification.
And what has been done to the condenser?
As someone who sells condenser tubing for a living I am always curious.
Leaks in a seawater condenser? sounds like very poor workmanship. This is serious premature failure.
Condenser life should be in the range of 20-40 years.
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Plymouth Tube
RE: Microfissure
I've seen some major workmanship problems with Condensers in the past two/three years. Owners and their Engineers are often highly remiss in their attention to Supplier surveillance.