How to protect high-pressure heat exchangers during shutdown?
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After being shut down for 6 months, our company’s high-pressure heat exchanger is ready to resume operation. During the hydrostatic test, large-scale leaks were found in the heat exchangers; in two of them, nearly 1/3 of the tube bundles were leaking. During the shutdown, these high-pressure heat exchangers were subjected to purging, displacement, neutralization, and nitrogen protection measures. Since this shutdown is due to technical upgrades, one of them needs to be removed. To prevent fires or explosions during the cutting process, water seals were installed on the inlet and outlet pipelines before cutting; after cutting, the water in these seals was drained, and the pipes were then covered with plastic sheeting until it was time to resume work. But I didn’t expect such a large-scale leak to occur. I would like to ask: What were the shortcomings in the handling of the heat exchanger during this shutdown? 2 How should heat exchangers that have been out of use for a long time be protected?
I’m just waiting for an expert to provide an analysis; I also want to learn* learn*.
This post was last edited by qdxf on 2019-10-25 at 14:12. It is best to use water protection during the shutdown of the high-pressure heater; do not allow the water to drain out and dry it out. Internal corners are difficult to dry. During long-term shutdown, use a sealed system with water to provide protection. While the system is shut down, pay attention to the safety valves on the bypass lines to prevent deformation caused by temperature differences (freezing or thermal expansion). The typical blockage rate for high-pressure pipes is 10% to 15%; at 30%, they need to be replaced. I’ll work on this thing right away; you can contact me if needed.
Protect with water? ? ? ? What water? ? The demineralized water I use is that good.
Was there a leak before parking that went unnoticed?
Secondly, if it is a carbon steel pipe, it must be due to excessive moisture; the wall thickness of the pipe has decreased significantly. Generally, nitrogen sealing provides an excellent pressure retention effect
Gao Huan uses S321 stainless steel pipes, which offer good resistance to hydrogen corrosion as well as general corrosion. If there is a leak before the shutdown, then the high and low pressure heat exchangers will show some reaction, and that’s what confuses me. Work has stopped before as well, but I’ve never encountered such a situation. Because of this, the installation will have to start several months later. The main problem is that I can’t find the cause; I don’t know how to prevent it, which is frustrating.
These are your operating conditions. Material. Properties of shell-and-tube media. There is no information provided regarding the material of the heat exchanger or the design pressure temperature. How was it combined? Service life. There’s nothing. How can I analyze it?
Perhaps I didn’t explain myself clearly enough; let me describe the working environment: it involves heat exchangers in a diesel hydroprocessing unit, with an operating pressure of 7.5–8.2 MPa and temperatures ranging from room temperature to 365°C. The heat exchangers used are high-pressure models manufactured by Fumi. The shell side of the heat exchanger carries the feed oils (E1101 and E1103A/B) as well as the material that has undergone reaction and then passed through the fractionation towers after going through the high/low temperature separation unit and desulfurization tower (E1102), while the tube side carries the material that comes out after the reaction. The raw materials are coker gasoline and diesel, as well as Changchai and catalytic diesel. Room temperature refers to the temperature at the inlet of the raw materials, while 365°C is the temperature of the material as it exits after the reaction. For this technical upgrade, since work involving open flames was required and there was a risk of fire, flash explosion, or hydrogen cracking in the pipe bundles, the passivation process provided by a company in Zibo named Dunhua and Zhonghe was adopted. It is not clear what the raw materials used for the passivators and curing agents are. I’m not sure if this explanation is clear.
Oh, I forgot one thing: the service life is around 5 years. I hope experts can help analyze this. Also, since the heat exchanger is leaking, it will take a few months to get a new one. So what should be done to prevent freezing in winter? ? Thanks first! ! !