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Re: How overheating can take place in such location?

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Posted by Dave Sawicki on May 14, 2002 at 00:46:35:

In Reply to: How overheating can take place in such location? posted by SOVAN on May 12, 2002 at 00:34:57:

: We have BHEL make VV 40 boiler of 180 T/hr, 96 Kg/cm2 and 510慢 (Natural circulation, corner fired boiler). Recently we have waterwall tube failure of fish mouth opening type. Location of leakage is on the roof tube (riser). At the time of failure boiler was on full load i.e. 185 T/hr, 500慢 and 100kg/cm2 pressure. Drum level was quite normal. Suddenly tube failed and boiler tripped on flame failure and after leakage water level fell down.
: Thicknesses of the surrounding tubes were found normal. Tube failure occurred after 45 days of operation after annual overhauling and inspection.
: How overheating can take place in such location? (Preliminary reason of tube failure was starvation) What are the probable causes of starvation at this location (35th tube out of 83 tubes).
: Will appreciate a reply. Thanks.

I fully concur with Pete - AND the original finding of OVERHEATING. Apparently an object appears to have fallen down that particular tube from the steam drum. Was there any foreign objects found lying anywhere on the firebox floor? A "Thick-Lipped" rupture as you have described occurs from rapid, localized overheating. The item lodged in the tube restricted the volume of "cooling" water flowing through the tube. Given the location of said tube, i.e. a Firebox water wall tube, there is no doubt in the cause of this failure. Had this same failure occurred further back in the main generating bank the results would have been a "Thin-Lipped" rupture caused by prolonged overheating. This causes the tube to first bulge and then rupture. To prevent against such a failure in the future I strongly recommend you implement a new procedure when entering the steam drum for ANY reason. That is simply the the individual/s entering remove ALL items from their person i.e jewelery, coins pens etc. Items required by the entrants should be handed in by the attendent outside and an inventory made of all items which have entered into the boiler. Upon the individuals exit from the drum, ALL items on the list MUST be accounted for. If not, a Tube Search should be conducted, preferably using an electricians wire snake. Happy Steamin' - Dave

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: : We have BHEL make VV 40 boiler of 180 T/hr, 96 Kg/cm2 and 510慢 (Natural circulation, corner fired boiler). Recently we have waterwall tube failure of fish mouth opening type. Location of leakage is on the roof tube (riser). At the time of failure boiler was on full load i.e. 185 T/hr, 500慢 and 100kg/cm2 pressure. Drum level was quite normal. Suddenly tube failed and boiler tripped on flame failure and after leakage water level fell down. : : Thicknesses of the surrounding tubes were found normal. Tube failure occurred after 45 days of operation after annual overhauling and inspection. : : How overheating can take place in such location? (Preliminary reason of tube failure was starvation) What are the probable causes of starvation at this location (35th tube out of 83 tubes). : : Will appreciate a reply. Thanks. : I fully concur with Pete - AND the original finding of OVERHEATING. Apparently an object appears to have fallen down that particular tube from the steam drum. Was there any foreign objects found lying anywhere on the firebox floor? A "Thick-Lipped" rupture as you have described occurs from rapid, localized overheating. The item lodged in the tube restricted the volume of "cooling" water flowing through the tube. Given the location of said tube, i.e. a Firebox water wall tube, there is no doubt in the cause of this failure. Had this same failure occurred further back in the main generating bank the results would have been a "Thin-Lipped" rupture caused by prolonged overheating. This causes the tube to first bulge and then rupture. To prevent against such a failure in the future I strongly recommend you implement a new procedure when entering the steam drum for ANY reason. That is simply the the individual/s entering remove ALL items from their person i.e jewelery, coins pens etc. Items required by the entrants should be handed in by the attendent outside and an inventory made of all items which have entered into the boiler. Upon the individuals exit from the drum, ALL items on the list MUST be accounted for. If not, a Tube Search should be conducted, preferably using an electricians wire snake. Happy Steamin' - Dave

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