There is a case regarding internal leakage in a safety valve; I hope **you can help take a look at it
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This post was last edited by qcswfzsdzf on 2017-6-7 09:58. We distribute safety valves of the Xfu brand, sourced through legitimate channels. The customer is a boiler manufacturer; the operating conditions are steam at temperatures not exceeding 180 degrees Celsius, with an operating pressure of around 0.78 MPa. Recently, a strange phenomenon has emerged: although the valves pass all the tests conducted during regular inspections, many of them develop leakage issues at their sealing surfaces after just 1 month of use, or at most 2 to 3 months; in other words, there is internal leakage, and in some cases the valves even start to malfunction prematurely. The explanation given by the factory is usually that the sealing surface is damaged; the valve has been disassembled, and there are indeed some small pits on the sealing surface. Question 1: Does the seal surface leak first and then get damaged, or does it get damaged first and then start leaking? Another detail is that the supply is generally done at a set pressure of 1.0 MPa, with the pressure range being 0.8 to 1.0 MPa. Customers will make appropriate adjustments at the boiler inspection agency based on actual conditions; some adjust it to 0.85, while others adjust it to 0.88, which is roughly 1.1 times the operating pressure. The factory recommends shipping it at the actual set pressure. Question 2: Could adjusting the set pressure within the pressure range specified by the pressure testing institute affect the performance of the valve? Question 3: Are there any practical experiences, whether they are simple methods or crude approaches, to solve this problem? For example, set the pressure value higher, and also report a higher working pressure to the boiler inspection agency? (A suggestion I’ve heard) Thank you so much!
Is there skill involved in knocking? Trying before didn’t work. Is it useful to tap, or is it due to spring offset?
1. If the sealing surface is damaged, the possibility of manufacturing quality defects in the factory should be considered. For example, the thickness of the welded seal surface, and whether there is any mixing of the base material in the weld layer (single-layer welding) can be checked using certain reagents. Under this pressure, even a leak should not cause damage to the sealing surface. 2. The adjustable set pressure range of the safety valve spring should cover the actual operating set pressure of the safety valve; it is generally advisable to set it at the midpoint. For example, if the set pressure is 1.0 MPa, the adjustment range for the spring can be chosen as 0.9–1.2 MPa. The purpose of users increasing the set pressure is, on one hand, to facilitate production management; operating the device at a slightly higher pressure than the designed value may improve production efficiency. The second aspect is to avoid frequent activation of the safety valve, which causes frequent fluctuations in pipeline pressure and affects production. 3. The calibration pressure at the testing institute is set based on the parameters indicated on the product’s nameplate; if the user specifies a higher operating pressure, then the values on the nameplate of the product leaving the factory must also be adjusted. Safety valves are safety accessories for pressure pipelines; altering their design parameters without authorization can create serious safety hazards, making them a source of risk for work-related accidents.
Personally, I think that safety valves used with steam may face issues due to instability in the steam pipeline system, which can result in air currents impacting the sealing surfaces. When pressure drops, water from the saturated steam will precipitate, leading to bubble corrosion at those sealing surfaces.
This post was last edited by CHANGBAISHI on 2017-6-8 at 11:30. The quality of safety valves is ensured by strict manufacturing standards, so quality concerns can be disregarded. The setting of the discharge pressure for the safety valve is determined based on the usage requirements. Within the operating range of the safety valve, data is provided to the relevant testing authorities, who, after adjusting and verifying it using the data you provide, seal it with a label. When in use, it is best to stay away from this starting value; once it starts operating, if it cannot be shut down promptly, the pressure must be reduced to the reset pressure specified by the safety valve in order to shut it down. If it has not been closed yet, it is necessary to take it offline, develop a new valve port, perform pressure testing and leak checking; once it passes these tests, it can then be taken to the relevant departments for final adjustment. Remember, under no circumstances should you adjust or use it without the confirmation of the relevant professional department; otherwise, responsibility will be pursued in case of any issues. (For reference)
I think the valve core should be made of a material that is one grade higher than that of the valve body, with an alloy welded on it
This hard seal is not completely airtight; whenever there is a fluctuation in steam pressure, leakage may occur
Agree with the reason given on floor 5. In your case, it’s best to consult the safety valve drawings and conduct a spectroscopic analysis to determine the material of the sealing surface in the corroded area; if this material differs from what is specified in the drawings, then the manufacturer’s quality control is inadequate. If they match, then upgrade the material. I have never encountered a situation like yours; the sealing surfaces of our safety valves are all made of 316 material, and I have never seen any corrosion on those sealing surfaces
The issue with safety valves cannot be ignored. My workshop also experiences the same problem you described; even after adjusting the set pressure, the valve still trips after some time. The only solution is to replace the valve, as it’s mainly the spring that has become fatigued