Kettle reboiler tube box, S30408: crack in the circumferential seam above the partition; the lower part is normal
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This post was last edited by chen3291 on 2018-1-17 at 10:58. The operating conditions are added here: it is a tube sheet for a kettle-type reboiler, with 4 kg of steam flowing in the tube side; the material used is S30408, with a wall thickness of 6 mm. The steam is industrial steam from the factory site. There is another operating condition related to cold materials: in such cases, the factory uses circulation water channel manifolds. This circulation water is very dirty and yellow in color, probably due to rust inside the steel pipes. Now, the circumferential seams above the tube bank partition are cracked, while those below the tube bank partition are not cracked. Analyzing this operating condition, samples have been taken from the circulating water and steam condensate, and it was found that there are significant amounts of chloride ions in the circulating water. Samples taken from the condensate tank also contained high levels of chloride ions. Even if chloride ions cause corrosion, why are there cracks above the partition while there are no cracks below it?
It might be related to temperature; the temperature above the partition is relatively high.
It is corrosion caused by chloride ions; the upper part of the pipe box is severely corroded. The upper part of the pipe box is where the steam enters, and temperature also plays a role in this. Use 22053 material instead
This post was last edited by xlxuiin on 2018-1-18 at 11:01. Someone shared this post a few days ago, but no relevant operational data was available; it has now been supplemented. Firstly, the chloride ion level in conventional circulating water is generally kept quite high (below 1000 ppm). However, many plants’ circulating water systems use stainless steel equipment and components, and no corrosion or damage caused by chloride ions has been observed (such as in plate heat exchangers). Secondly, the factors affecting chloride corrosion include temperature, concentration, pH value, etc. Third, this is a condition of alternating hot and cold temperatures; improper heat treatment of the tube box or incomplete elimination of welding stresses are likely the main causes of fatigue cracking. Fourth, whether the partition has drainage holes; chloride corrosion is not the primary cause. For reference only
It is estimated that the cracking was caused by chloride ions
This circulating water is yellow; there must be a lot of iron ions in it. These iron ions contaminate stainless steel, and it’s possible that this is the reason why a proper passivation layer cannot form on the stainless steel, resulting in a lack of corrosion resistance. Normally, such steam-using tube boxes have been manufactured many times before, and this is the first time I’ve heard of such an issue. The temperature and pressure in these tube boxes aren’t high actually; there are conditions with higher temperatures and pressures as well, but no problems have occurred there
The temperature difference on both sides of the partition for another U-shaped heat exchanger should not be very large; generally, the latent heat of vaporization of steam is utilized for heat exchange, and the temperature of the steam itself should not change much
1. The temperature difference measured last time on the tube bank partition was not significant. 2