Tube to tube sheet welding failure
Tube to tube sheet welding failure
(OP)
We have a Low pressure steam boiler. It operates at around 45 kg/cm.2. Its a kettle type heat exchanger with straight tubes. Recently leakage was observed in the boiler.Inspection reavaled, that 06 tubes failed & many places tube to tube sheet weld leak was observed . The tubes are SA179 tubes. Steam is on shell side & tubes carrying the hot gases. It is importnat to note that All leaks were obserbed on the inlet side lower half (inlet tube sheet temp. is approx 570 Deg. C whereas outlet temp. is around 250 deg c). What could be the reason of this failure ? Inlet side shell support legs are fixed type where as outlet side shell support legs are floating. Upon inspection, it was observed that the tubes are bent along the length. This observation was made while peeping through the tubes.
Necessary repairs have been carried out.
WIll any one share his view about the problem & share the experience.
Necessary repairs have been carried out.
WIll any one share his view about the problem & share the experience.





RE: Tube to tube sheet welding failure
How are the tubes installed into the tubesheet? Rolled and seal welded or strength welded?
Can you explain the type of tube to tubesheet leak - crack or separation or other?
RE: Tube to tube sheet welding failure
The tubes are installed horizontally with a strength weld & the defects were porosities ( in some tubes big poros )
RE: Tube to tube sheet welding failure
This sounds like it was poor workmanship of the tube to tubesheet welds from day 1. How long has this low pressure steam boiler been in service? Is this the first time these weld failures have occurred?
{Sorry for my repeated questions, but sometimes it provides valuable input to others and myself to help you}.
RE: Tube to tube sheet welding failure
RE: Tube to tube sheet welding failure
RE: Tube to tube sheet welding failure
OP
That is why
RE: Tube to tube sheet welding failure
Any new idea please ??
RE: Tube to tube sheet welding failure
Can you post any pictures of the tube to tubesheet failures or provide a better desription other than pores? To a metallurgist, when I hear pores I immediately think of porosity which translates back to poor workmanship. By the way, depending on the welder or welders you could have defects confined to a particular location on the tubesheet, so don't necessarily rule it out.
I only suggested workmanship as a possibility. Without seeing the failure first-hand or reviewing pictures, it certainly could be thermal/mechanical stresses that are attempting to overload the weld joint.
RE: Tube to tube sheet welding failure
RE: Tube to tube sheet welding failure
RE: Tube to tube sheet welding failure
RE: Tube to tube sheet welding failure
I suppose that the tube bending is the result of heat exchanger poor design. Normally kettle type exchanger has a floating head for tube bundle expansion. If the tubes cannot expand the tube welds into tube sheets will be stressed and weld failures will occur. If I were you I will revue exchanger design and strength welds procedures.
luis marques
RE: Tube to tube sheet welding failure
How many cycles has the unit seen. Cylic service at the high temperature gradients can easily lead to leakage at the tube-to-tubesheet joints, especially at pore sites in single pass welds. Were the tube-to-tubesheet weld 2-passes or one? Porosity is also often seen at the tie-in locations; is porosity throughout the weld or localized?
RE: Tube to tube sheet welding failure
Would it be possible that the level control system malfunctioned causing the shell side fluid to evaporate completely while allowing hot tube side gas to flow?
RE: Tube to tube sheet welding failure
Consider posting this question on a more boiler oriented forum:
www.steamforum.com
Let us know about you final decision....
-MJC
RE: Tube to tube sheet welding failure
We have found some indicative history of boiler running with very low water levels in the shell. So as, I am convinced the bent tubes are the result of execssive heating of tubes due to water starvation, This would have caused loading on tube tube sheet joints also, casuing TTS weld failure at many places.
Thank you forum for the support & share