I would like to ask about the reasons for leaks in the heat exchange tubes of the waste heat boiler evaporator! ! ! Waiting online
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The image below shows the leakage of the heat exchange tubes in the evaporator of our company’s waste heat boiler. The structure of the evaporator consists of an upper header and a lower header, connected to each other by heat exchange tubes. The heat exchange tube has bends at both the upper and lower parts. The equipment has been in operation for less than two years when leakage occurred at the bent parts of the heat exchange tubes. There are no issues with the straight section of the heat exchange tube (the straight section includes fins). Our company’s analysis of the reasons is as follows: 1. Low-temperature corrosion occurred in the heat exchange tubes, leading to perforations in these tubes and subsequent leaks. 2. There is an issue of external erosion of the heat exchange tubes; the erosion caused by flue gas leads to thinning of these tubes and subsequent leakage. But both of these reasons for analysis seem incorrect. If it’s a problem with corrosion and erosion, why are only the middle heat exchange tubes leaking? The other heat exchange tubes are intact (no signs of corrosion or erosion on their surfaces; they are quite clean). And only the bent parts are corroded. There are no issues with the straight section of the heat exchange tube. The flue gas temperature at the inlet of the waste heat boiler evaporator is less than 300 degrees Celsius. The boiler pressure is 0.8 Mpa. Please help analyze this. Thank you so much
Problem with the leakage site of the heat exchange tube: The wall thickness remains unchanged in the straight section, while it is relatively thinner in the bent section. Location of the leaking heat exchange tube: Check the flow direction of the medium as shown in the diagram; is the flow rate uneven among the heat exchange tubes in different areas, and is the flow rate and velocity higher for the tube that is leaking? With all other conditions being the same, greater flow rate and velocity mean more pronounced erosion and corrosion. It’s just my personal guess; it has no basis at all. ;P;P;P
I have also considered what you mentioned. It’s at the elbow without fins; there are no fins at that elbow, so the resistance is low, and the flow of flue gas creates erosion. What I don’t understand is why only the middle ones are missing. If it is erosion, will the heat exchange tubes at the flue gas inlet be the first to be damaged by erosion?
This post was last edited by pzhmotor on 2024-3-17 at 11:18. It is recommended that the original poster pay close attention to checking for any leaks in the tank and side walls surrounding the area where the waste heat boiler has a leak! Waste heat boilers are usually under negative pressure, and the two leak points found were located near the lower header, not in areas with severe erosion. If the outer wall seal is not proper, air will be drawn in, causing localized low temperatures and leading to dew point corrosion. It is recommended to check whether the series connection is set up as required, and to carry out regular sewage discharge. Check the inner wall of the pipeline; it is recommended to verify whether the feed water meets the requirements for low-pressure boilers. (The key parameters are conductivity, pH, and oxygen content.) If the water quality does not meet the standards, it affects the stability of long-term operation.
The bending process at the elbow section is not carried out properly; the wall thickness reduction exceeds the allowed limits, and the flattening of the elbow is also beyond acceptable levels. This area is subject to high scouring forces and stress concentration, which makes leaks more likely to occur.
Check the feedwater parameters to ensure that the phosphate level is within the range of 10–50 mg/L
Excessive bending leads to reduced wall thickness