Reasons for the formation of dense cracks on U-shaped heat exchange tubes
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It is a methanol distillation vessel with a U-shaped tube bundle in its lower part; the material used for this bundle is S30408. Saturated steam at 0.5 MPa flows inside the tubes. The equipment has been in use for almost a year, and due to leaks in the heat exchange tubes, it was taken apart and it was found that several of these tubes had dense cracks as shown (while the surface of some other tubes remained smooth). Let’s discuss what could be the cause of this.
Is the cracked pipe near the shell-side inlet? It could be scouring corrosion.
Ordinary air cannot corrode stainless steel
When tubes are cold-drawn or cold-rolled, their surface quality is poor, and surface defects appear as a result of corrosion
Pot-type evaporator, without scouring
Are the finished heat exchange tubes qualified for inspection? Where on the shell side is the faulty heat exchange tube?
On the surface, it appears to be intergranular corrosion
If the temperature exceeds 100°C, corrosion of the equipment becomes severe. Stainless steel has strict requirements regarding halogen elements (Cl, F) in the raw materials, as these elements cause corrosion in stainless steel at any temperature.
When steam condenses into water, fluid shock occurs, generating vibrations that lead to cracks.