What are the common reasons for tube failures in the water wall of gas boilers?

This is a difficult question to answer. Could you please explain in detail the location of the burst pipes? For example, in the nozzle area? Superheater? Which area again? The reasons for tube bursts may vary in different areas. 1. For gas boilers, there is a high likelihood of a reducing atmosphere existing inside the boiler; it is necessary to check whether there is any reduction corrosion occurring. 2. Analyze the causes of tube failure for different parts of the boiler. 3. Perform metallographic analysis on the damaged tubes to determine the direct cause of the tube failure, and then analyze the combustion and flow issues within the boiler.

There are many reasons for tube rupture. Possibilities: 1. Improper operation led to excessively high local temperatures. 2. Scaling on the pipe wall 3. Failure to perform soot blowing in a timely manner

If the tubes in a boiler’s water wall burst and there is no issue with the material of those tubes, it is usually caused by local overheating. There are various reasons for local overheating; for example, too low a boiler water level can lead to poor water circulation, resulting in a lack of water in some of the water wall tubes. The boiler load is too low, resulting in a slow water circulation. If the gas nozzles are not distributed evenly, the heat distribution within the furnace will also be uneven. Another issue is that the flame from the burner is too long and burns the tubes directly; this is the most common phenomenon. Therefore, during boiler operation, it is required to adjust the burners to operate with multiple burners and short flames.

May I ask if the gas used in your boilers is natural gas? If so, it would be advisable to conduct an analysis of the sulfur content in that natural gas. It’s possible that the sulfur content is high; when sulfur burns, it produces SO2 and SO3, which then react with water vapor – a byproduct of methane combustion – to form sulfuric acid or sulfurous acid. This substance can then corrode the water wall, leading to tube failures. If the boiler is large, the amount of natural gas used is high, and the sulfur content is high, it is possible to consider installing an MEA desulfurization system to reduce the sulfur content in the fuel and extend the service life of the water wall ； Additionally, it is recommended to conduct a thorough non-destructive testing of the water wall in order to assess the extent of its damage and carry out thorough repairs, thereby avoiding frequent shutdowns for maintenance.

(1) Consequences of tube rupture. Tube explosion refers to the rupture of the tubes in the boiler’s evaporation heating surfaces during operation, including the rupture of water wall tubes, convection tube bundle tubes, and flue tubes. When a furnace tube bursts, a blasting sound can often be heard; subsequently, the water level drops, the pressure of steam and feedwater decreases, there is a sound of steam and water spraying out from the furnace or flue, the negative pressure diminishes, the combustion becomes unstable, the feedwater flow rate is significantly higher than the steam flow rate, and sometimes other noticeable symptoms appear as well. (2) Reasons for tube rupture. ①Poor water quality, pipe scaling, and overheating leading to explosion ； ②Water circulation failure ； ③Severe water shortage ； ④Foreign objects such as steel balls and wooden plugs fall into the pipe during manufacturing, transportation, and installation ； ⑤Flue gas erosion causes the tube wall to thin out ； ⑥The tube walls that are in operation or have been shut down down due to corrosion have become thinner ； ⑦Tube expansion is hindered, resulting in cracks due to thermal stress ； ⑧Improper soot blowing leads to thinning of the tube wall ； ⑨Tube tree defects or welding defects develop and expand during operation. (3) Tube burst treatment. When the furnace tube bursts, it is usually necessary to shut down the furnace urgently for repairs. Since there are many reasons that can lead to the explosion of furnace tubes, and accidents often result from the combined effect of several factors, preventing such explosions also requires attention to all aspects such as boiler design, manufacturing, installation, operation management, and inspection.

Regarding the frequent tube ruptures mentioned by the poster, and the fact that there is no issue with water quality, I think the causes can be investigated from the following aspects: 1. Wear caused by flue gas or improper soot blowing, which leads to thinner tube walls and thus tube ruptures. I wonder if the original poster went inside the furnace to check where the tube burst, to see if it was caused by wear that thinned the tube walls and led to the burst ； 2. Has there been frequent starting/stopping or load changes recently? When changing loads, the rate of temperature change should be slow; otherwise, tube rupture is likely to occur, especially in furnaces that have been in operation for a long time. This post was last edited by yi3436 on 2008-10-16 12:29.]

The original poster did not describe the characteristics of the area where the tube burst, such as whether there was any overheating on the surface of the tube, the structure of the boiler, and the exact location of the burst. If overheating occurred, it was likely due to poor water circulation, probably a result of design issues; if corrosion was present as well. Factors such as fuel issues need to be taken into account.

It would be best to send a photo of the area where the pipe burst, so that it can be analyzed more easily. In the case of gas pipes, there is likely no external erosion or dust accumulation; it’s more probable that overheating of the pipe wall due to scaling on the water side caused the pipe to burst.

I guess the boiler is probably of the SZS type. From what the poster has described, the water-cooling system has been experiencing frequent pipe bursts over these months; it’s likely that there isn’t a problem with the pipes themselves, as all materials supplied by the boiler manufacturer go through re-inspection before being used. At most, 1 or 2 pipes might have defects such as sand holes, but this probability is extremely low. It is possible that the water circulation in the boiler is poor, and the ratio of the rising tubes to the descending tubes is not optimal; as a result, the velocity of the homogeneous water is low, leading to the formation of a stratified layer.

Based on what was said above regarding frequent pipe bursts, I believe it is caused by poor quality of water used in the boiler, or rather, by inadequate water treatment. Poor water quality leads to severe scaling, and poor heat conduction can result in pipe bursts in the boiler； Erosive corrosion generally takes a long time to occur; it doesn’t result in pipe failures on a regular basis as the poster mentioned. The material itself should not be the problem either – if there were an issue with the material, there would be pipe failures on a large scale. It is recommended to strengthen water quality monitoring and use better water treatment chemicals.

The water-cooling wall tubes in the rear furnace wall of the gas boiler have burst; there are no signs of corrosion or erosion on the outside of these tubes (as a 3 CM thick fireproof layer made of high-alumina cement was applied to their exterior). The water quality is checked daily and it is within acceptable limits, so there should be no problems. All the recent tube bursts were discovered after the boiler was shut down. Seeking advice from experts