×
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

Water boiler tube burst

Water boiler tube burst

Water boiler tube burst

(OP)
Some days ago we have had a water boiler tube burst. Burst location was in a radiant rear water tube at the top convection zone on an almost horizontal part of the tube, about 1,5 m from the top water tubes header. First visual inspection of damaged tube was a typical failure of a "thin-lipped" burst of the boiler tube. This type of failure results in a ductile rupture of the tube metal and is normally characterized by the classic “fish mouth” opening in the tube where the fracture surface is a thin edge.
 After a closer microscopic microanalysis of the thin edge and good tube zones we didn’t found any differences in the microstructures between thin edge and adjacent good tube zones. No evident distortion of ferrite and perlite was seen.
 For that reason we think the failure has occurred well below the lower critical transformation temperature with no evident distortion of ferrite and perlite.

Adjacent tubes don’t reveal any plastic distortion or diameter tube growth. After digital Rx examinations we found that adjacent tubes of boiler tube burst showed great thinning on top of part of the tubes at 12 o’clock location, the thinning was about 250mm long. Nominal tubes thickness is 5.6mm and thinner point in 250mm length was 1.5mm.Thickness of bottom part of the tubes were ok.

Due to the facts my conclusion is: tube failure cannot be explained by a short term overheating.

My question is can we explain the thinning on top of the tubes by cyclic turbulent erosion of wet drops of steam?

Tube goes 15m in a vertical run and then it turns almost horizontal within 2m after connecting with the upper water boiler header. On the vertical part of the tubes there is a equilibrium between water and diffused steam bubbles, but on the horizontal part of the tubes about 1m of the turn bend, by differences of densities the water runs on the lower part of the pipe and the drops of wet steam run turbulently above the water inducing high erosion on that 12 o’clock location of the tubes.

My intention is to warning other operators for this kind of failures and to have comments from the forum on my conclusions.

Tanks

Luis Marques

RE: Water boiler tube burst

This sounds like internal wastage caused by a steam blanketing effect during flow conditions through the horizontal boiler tube. This is a damage mechanism I have seen in horizontal roof tubes in a power boiler. The wastage occurs along a narrow band along the top of the horizontal oriented tube.

RE: Water boiler tube burst

I don't think the steam is the source of your failure.

Fly ash erosion?  Is it a coal boiler?

Reducing environment?  Could this area of the boiler be more starved for oxygen?

Gene Grindle PE

RE: Water boiler tube burst

I believe the wastage is from the ID side of the tube.

RE: Water boiler tube burst

(OP)
Thank you for your answers!

metengr

I totally agree with you our tubes internal wastage is occurring exactly in a narrow 12 o’clock band on row tubes adjacent to the burst one.

ggrindle

The wastage is internal (water side of tubes) so it cannot be attributed to fly ash erosion.

Boiler burns fuel or fuel gas

Regards

Luis Marques

RE: Water boiler tube burst

aaaaaahhh

did not get that it was internal ID that was wasting away.

I have no first hand experience with that mode of failure.

If indeed you do have 2 phase flow in this area, that might explain it.  

good luck.

RE: Water boiler tube burst

0707

I have a question
when did tube rupture?

operiting or start-up


RE: Water boiler tube burst

What is the boiler rated for Lbs/hr and what is your actual peak firing rate?

could it be erosion due to over-firing?

RE: Water boiler tube burst

I agree with metengr's post of 6/26.  You can correct this by using rifled tubing in these areas to increase the turbulence through the tube.

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