×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Microfissure

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.

RE: Microfissure

Were the welds dissimilar metals welds? In weld metal or fusion line? How did they measure so accurately with fiberoptic scopes?

RE: Microfissure

One other question. Was operation base load or intermittant (peaking)?

RE: Microfissure

What was the orientation of the visual indications relative to the weld root?

RE: Microfissure

Also, for a typical tube to header connection for an HRSG, the weld joint is typically a partial penetration weld between the tube and header and visual examination of the weld root would not be possible. Instead, the so called microfissures could be ligament cracks in the header bore hole. This would need to be confirmed by someone.

RE: Microfissure

(OP)
Sorry for the late reply, kinda busy this day.

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

Intergrannular cracking is indicated. It appears to be in both the weld metal and HAZ. Possible environmental cracking. More info is needed. How did you introduce sea water into the boiler feed stream? In this case most likely all of your water treatment is in question - pH, Oxygen content, etc.

RE: Microfissure

(OP)
There was a leak in the surface condenser which caused the seawater ingress.

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

For the new Harp, hydrogen cracking. Inadequate preheating. Delays between weld completion and PWHT. Finally inadequate PWHT and highly dissimilar heating and cooling rates of tube and header.

High temp Creep is intergrannular.

RE: Microfissure

Quote:

How dangerous are the cracks?

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

How was the new harp hydrotested/drained. Water quality, inhibitors added?

RE: Microfissure

Regardless of how these initiated (I would side with EAC) the risk of thermal fatigue causing a failure from these is very high.

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.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Microfissure

Ed,
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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources