09-02-20 Topic — How to determine internal leakage in high-pressure feedstock heat exchangers? Explain the reasons (Participation rewards available)

Please explain the process flow and equipment structure; it seems to be necessary to consider the temperature changes of the hot and cold fluids

It can be determined based on the following points: 1. Judge by the import and export temperatures. 2. Analyze changes in the composition of the medium.

There are too many missing criteria for the topic. Please provide the basic information: 1. Type of heat exchanger: Steam heating? Cooling with cooling water? Import and export pressures? Temperature? 2. Raw material type: Flammable? Non-flammable? How high is the pressure? Basic physicochemical properties? Without these basic conditions, what’s there to discuss? ? ?

It’s better to provide more conditions; generally, when the temperature and pressure on both sides of the heat exchanger change, the color of the shading will also change. :)

Please explain the process flow and equipment structure; it seems to be necessary to consider the temperature changes of the hot and cold fluids

1. Pressure change (if the pressures on both sides are not equal, the pressure change is quite significant) 2. Temperature change 3. Medium change

My design approach is to install a hardware pressure switch on the low-pressure side; if there is a leak on the high-pressure side, the pressure switch on the low-pressure side will activate, thereby providing chain protection for the heat exchanger: victory:

Here is an article: A paper on the analysis of internal leakage in high-pressure threaded locking heat exchangers. High-pressure threaded compression heat exchangers are suitable for high-pressure applications. For example, the high-pressure heat exchangers used in the hydrocracking units of refineries have a design pressure as high as 18 MPa. This heat exchanger is difficult to manufacture and requires high sealing performance. The Hydrogenation Section 2 of the refinery at Daqing Petrochemical Company is equipped with two high-pressure threaded lock-type heat exchangers (designated as E-3101A/B). On September 3, 2004, a leak was detected in one of the high-pressure heat exchangers; on September 9, technicians from the manufacturer tightened the inner bolts to a torque of 1200 N.M, after which no leaks were observed. On December 24, 2004, an emergency shutdown was triggered due to a false indication of the bearing temperature of the hydrocracking cycle hydrogen compressor, which resulted in overheating of the bed at the outlet of the hydrocracking reactor (to 880°C) and an inlet temperature of High Pressure Heat Exchanger A reaching 550°C. On January 14, 2005, after the sulfur content in the tested heavy naphtha was found to be above the acceptable level, the workshop determined that there was an internal leak in the high-pressure heat exchanger, with a nitrogen content of 17 ppm. The workshop promptly contacted the Mechanical Department and Fushun Machinery Manufacturing Co., Ltd. to handle the issue. On January 16, after the personnel from the Fushun manufacturer tightened the bolts on the outer ring of the two heat exchangers, a test showed that the nitrogen content was 11 ppm; however, internal leakage persisted. On January 18, following a decision made by the manufacturer along with the mechanical department and the workshop, the tightening torque was increased to 1250 N.M. Another test then revealed that the nitrogen content in the oil produced was 8.5 ppm. This led to the conclusion that there was damage to the internal components of the heat exchangers, and it was decided to suspend operations for repairs. 1. Equipment Overview: This equipment is manufactured by Fushun Machinery Manufacturing Co., Ltd. Main technical parameters: tube side design pressure 17 MPa, operating pressure 15.6 MPa ； The design temperature for the tube bank is 454°C, and the operating temperature is 415°C℃ ； The tube medium is the reaction product ； The shell side design pressure is 18 MPa, and the operating pressure is 17.1 MPa ； The shell side design temperature is 400°C, and the operating temperature is 373°C℃ ； The shell-side fluid is hydrogenated oil. Heat exchanger structure diagram (see Figure 1). Analysis of the causes of internal leakage. 2.1 Problems identified when the equipment was sent back to Fushun Machinery Manufacturing Co., Ltd. for repair and the methods taken to address them. 2.1.1 After removing the threaded pressure ring, signs of overheating were found in the threaded portion of the tube box (see Figure 2) ； The medium inside the tube is in the form of scale and sand particles (see Figure 3). 2.1.2 The internal and external top pressure bolts show no deformation, and their hardness meets the requirements. 2.1.3 After the sealing disk was removed, it was found to be deformed, but the hardness of its sealing surface still met the requirements specified in the drawings, with no significant decrease in hardness. During this equipment maintenance, all the sealing discs of the two high-exchange units were replaced. The old sealing disc has been sent back to the refinery, but whether it can be reused will have to be determined after further testing. 2.1.3.1 The gaskets used for external sealing have become deformed; new gaskets have been installed in both units. 2.1.3.2 The deformation of the brackets and compression rings was minimal; after cleaning, they were put back into use. The originally planned 2 spare parts have been returned to the refinery. 2.1.3.3 The internal top pressure bolts passed the hardness testing, but several of them had damaged threads; all the removed parts were returned to the refinery, and new ones have been installed on the equipment in their place. 2.1.3.4 The separating ring shows minimal deformation, and the threaded portion can be reused after being re-tapped. 2.1.3.5 The split boxes of both units were deformed; the condition of unit A was more severe, with an ellipticity of 17 mm. Even after repair, it could not be installed in the tube box, so a new split box was installed for unit A, while the old one was sent back to the refinery. 2.1.3.6 All gaskets and sealing strips have been replaced with new ones. Improves the sealing effect. 2.2 Analysis of leakage causes 2.2.1 Sealing principle of high-pressure threaded compression heat exchangers. The outer sealing gasket 1 isolates the medium in the heat exchanger’s tube side from the outside environment; it is compressed by the external compression bolts 2. The pressure from the tube box is transmitted to these compression bolts through the gasket, and from there it is passed on to the large-threaded ring 3. The trapezoidal threads on this ring then transmit the force to the tube box, which is in turn supported by the tube box cylinder. The clamping force of the internal pressure bolt 4 is transmitted via the internal pressure rod 5 → internal pressure ring 6 → inner sleeve in the tube box 7 → tube sheet 8 → to the internal sealing gasket 9, thereby isolating the media on the tube side and the shell side. Heat exchanger sealing structure (see Figure 5). 2.2.2 Cause of leakage: The inlet temperature of the high-pressure heat exchanger reached 550°C, which is well above the design temperature. This over-temperature caused the split-case to deform, resulting in uneven stress on the internal top compression bolts or a decrease in their preload. As a consequence, the gaskets in the shell side were not sealed properly; the graphite layer on the outside of these gaskets was worn away by the action of the fluid, leaving only the wave-shaped gasket material inside. When the external top compression bolts were tightened, without the graphite layer for sealing, proper sealing could not be achieved. 3 Summary: Preventive measures: It is strictly prohibited to operate the equipment at excessive temperatures, and the external top-pressing bolts must be tightened in accordance with regulations. Recommendation: The original gasket for the shell side was a corrugated composite gasket; however, this type of gasket is gradually being replaced by wound gaskets. Such wound gaskets are prone to leakage when the equipment overheats, and if leakage is not detected in time, the graphite surrounding the gasket can be washed away, resulting in a loss of sealing capability. In the case of winding gaskets, since the graphite is enclosed inside, the aforementioned phenomenon does not occur.

This has a lot to do with hot and cold fluid media. It mainly analyzes changes in pressure, temperature, flow rate, as well as changes in the properties of the medium.

1. Monitor the pressure changes on the low-pressure side. 2. Monitor the temperature changes at the ends. 3. Analyze the medium on the low-pressure side

It’s hard to answer when the conditions aren’t complete. It is necessary to specify whether it is for heating or cooling, whether water cooling or steam is used for heating, whether the process medium flows in the shell side or the tube side, and whether the process medium contains acids, is toxic, or flammable. A water-cooled heat exchanger, where the process fluid contains large amounts of acidic gases and the pipelines are under high pressure. The heat exchange tube has ruptured, which is indicated by the acidic nature of the outlet cooling water, with the acidity increasing over time ； Moreover, when the leakage volume is high in later stages, a bubbling sound of gas inside the heat exchanger can be clearly heard.

For internal leaks, it is not easy for operators to detect them directly, but they can be identified by abnormal temperatures, pressures, and flow rates of the medium, as well as unusual noises, vibrations, and other abnormal phenomena. For example, in a fertilizer plant, one of the heat exchangers uses circulating water as the cooling medium, which flows through the tube side, while the shell side is filled with syngas at very high pressure. When there are defects such as perforations in the heat exchange tubes or pores in the welds between the heat exchange tubes and the tube sheet, sampling can be taken from the cooling water inlet and outlet pipes of the heat exchanger for analysis; changes in pH value can then be used to determine whether there is a minor leak. When a leak occurs, the heat exchanger mentioned above will definitely experience large fluctuations in the cooling water pressure. The pipes and equipment produce significant abnormal noises and vibrations, and the explosion-proof plates on the cooling water pipelines may crack and leak, allowing for an immediate identification of a leak in that heat exchanger. If a liquid medium flows through the tube side of the heat exchanger at high pressure, it is also possible to open the drain valve on the gas line; by observing the normal drainage pattern, it is possible to determine whether there is an internal leak in the heat exchanger.

Since it is a high-pressure material, the pressure on the low-pressure side will definitely increase in the event of an internal leak. Also, check for any differences in the heat exchange medium; if there is a significant difference in color, it is possible to make a judgment based on the color. If it’s water, check whether there is oil in it. It depends on the specific circumstances

It is primarily determined by the differences in the state of the substances involved in heat exchange within the heat exchanger, such as temperature differences and concentration differences (which are even more significant when different substances are involved), which give rise to various changes in subsequent stages.

There must be instruments on the equipment; by checking the readings of the pressure gauge, flow meter, etc., it is possible to detect any abnormalities, and the outlet temperature will also change.

A preliminary assessment can be made based on pressure and temperature changes as well as medium analysis

Answer: Methods for detecting internal leakage in a heat exchanger: (1) Check the color of the high-pressure feed fluid; if its color darkens, there may be an internal leakage； ⑵It is possible to determine whether there is an internal leak in the heat exchanger by examining the components of the produced product and its odor. Reason: (1) Corrosion and leakage of heat exchange tubes ； (2). Cracking at the expansion joint (weld) between the heat exchange tube and the tube sheet ； (3) Sealing leakage at the floating head flange of the floating head heat exchanger. Solution: (1) Replace or seal the leaking pipe ； (2) Re-inflation (patch welding) or plugging ； (3) Tighten the bolts or replace the gasket.

How to determine internal leakage in a high-pressure feed heater: 1: Drop in feed pressure; 2: Change in the temperature of the feed at the outlet of the heater; 3: Change in feed flow rate. Last edited by jannes on 2009-2-20 10:55.]

The temperature difference between inlet and outlet, as well as the pressure drop across them, can also be determined based on the properties of the medium; it is necessary to analyze each case on a case-by-case basis.

1. Monitor the pressure changes on the low-pressure side. 2. Monitor the temperature changes at the ends. 3. Analyze the medium on the low-pressure side