Corrosion thinning of the inner curved surface of elbows
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Generally, corrosion-induced thinning of elbows on pipes occurs mostly on the outer curved surface; however, in some cases, it occurs on the inner curved surface as well. Has anyone encountered such a situation? Could you share it in more detail?
This issue requires specific analysis based on concrete examples. For example, such phenomena may occur in areas that are not used for a long time or where materials have accumulated and settled; this is provided for reference.
This is caused by uneven flow, with variable flow speeds; there are too many impurities in the fluid, as well as excessive air, which leads to erosion and cavitation.
It is recommended to use special materials – it’s worth spending money to avoid hassle: lol
Searchable: “Case Analysis and Control of Tower Top Corrosion in Atmospheric and Vacuum Distillation Units”. Fifteen days after the commissioning of a 10-million-ton atmospheric and vacuum distillation unit at an oil refinery in Qingdao, corrosion-induced perforations occurred on the inner curved surface of the outlet elbow pipe of the atmospheric tower’s naphtha dry air cooler (the tube bundle was made of titanium, while the tube box and elbow pipes were made of carbon steel). Cause analysis: The operation conditions of the electrodesalination unit were unstable. Electrodesalination was put into use 6 days after normal distillation operations began; a demulsifier was added 2 days later, and 3% water (based on the processing volume) was added 4 days later, resulting in an increase in the concentration of the corrosive substance HCl in the condensation system at the top of the tower ； The water injection volume at the top of the atmospheric pressure tower is too low, causing the initial solidification zone to shift towards the bend section of the dry air cooler ； After adding the neutralizing buffer, the pH value of the condensate water is low.
Check what type of elbow it is; if it is an elbow at the junction of horizontal and vertical pipes, and the pipes are not filled with liquid or the fluid is not homogeneous, this can lead to internal arc corrosion
This post was last edited by wswwsw3869 on 2022-11-28 at 12:06; it is related to the installation method of elbows, the properties of the materials, as well as the flow rate. It can’t be generalized. If the stretching surface of the elbow is facing upward, the material contains precipitates and the flow rate is not fast. Then the inner bend generally wears out first. If the elbow is facing upward at the highest point and there is no drainage, the upper wet surface is prone to rotning. ....
There are two reasons: 1. Medium corrosion – this relates to the choice of materials. 2. In cases where there is significant wear in special applications, it might be possible to increase the thickness of the elbows to reduce wear; additionally, it may be necessary to use wear-resistant materials as linings
This post was last edited by Wang Pei_KRYPo on 2022-12-7 08:52, with changes numbered 000