Material of the sealing surface for the ammonia stop valve
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I would like to ask fellow sailors for advice: After replacing the globe valves used in our ammonia storage facility, the new valves started leaking internally within less than a month of being installed. I wonder whether it would be better for us to use globe valves of the J41H series, or those of the J41P series, or perhaps those of the J41B series?
? Once a globe valve is in the open position, there is no longer any contact between its seat and the sealing surface of the disc; as a result, mechanical wear on these sealing surfaces is minimal. Moreover, since the seat and disc of most globe valves can be easily repaired or replaced without having to remove the entire valve from the pipeline, this is very useful in situations where the valve is welded to the pipeline. The flow direction of the medium changes as it passes through such valves; therefore, the flow resistance of globe valves is higher than that of other valves. The commonly used globe valves include the following: ?? 1) Angle globe valve ； In angular globe valves, the fluid only needs to change direction once, resulting in a lower pressure drop across the valve compared to globe valves with conventional designs. ?? 2) DC stop valve ； In direct-acting or Y-type globe valves, the flow channel of the valve body forms an angle with the main flow path; as a result, the degree of disruption to the flow pattern is less than that in conventional globe valves, and consequently the pressure loss across the valve is also lower. ?? 3) Plunger-type globe valve: This type of globe valve is a variant of the conventional globe valve. In this valve, the valve disc and seat are typically designed based on the plunger principle. The valve disc is polished to form a plunger that connects with the valve stem, and sealing is achieved through two elastic sealing rings fitted over the plunger. The two elastic sealing rings are separated by a collar, and the sealing rings around the plunger are pressed in place by the load applied to the valve cover by the valve cover nut. The elastic sealing ring can be replaced and is made from a variety of materials. This valve is primarily used for opening or closing, but it also features a special type of plunger or special rings that allow for flow regulation. I’m not an expert, but I hope this text is useful to you.
Reply to 2# woliaibo: Although it didn’t resolve my doubts, I still learned a lot. Thank you very much!
As you mentioned, the sealing surface materials of those globe valves are all of hard-sealing type. The characteristic of hard sealing is that its sealing performance is not as good as that of soft sealing; however, hard sealing can operate at higher temperatures, which is an advantage that soft sealing does not possess. H-seals are generally made of cast steel, P-seals are usually made of stainless steel, and B refers to babbitt alloy. I don’t understand why they are used in ammonia applications; if the temperature isn’t high, why not use J41F, which has a PTFE sealing surface? The sealing performance of this valve is definitely better than that of a hard seal, and that’s the main issue. Pharmaceutical versions can help answer such questions; those in charge of quality control are unable to assist with that, haha!
Ammonia is an alkaline substance; could it have reacted with the valve? I’m not sure what material your valves are made of; could it be a problem with the material?
Copper valves cannot be used with ammonia, as copper reacts with ammonia and causes corrosion. For ordinary ammonia or amines, carbon steel pipes are used, and these do not react with valves.
Reply to 4# nglcx2003cn: Learned something new! I basically know where to look for the problem now!
Product introduction of AJ45F-25 ammonia stop valve: This series of valves designed specifically for ammonia is developed to meet the special requirements associated with the transportation of ammonia and liquid ammonia. It takes into account the actual conditions of valve usage in China, and features innovative sealing methods as well as a reliable sealing structure. This type of valve features stable sealing performance, safe and reliable operation, strong corrosion resistance, no internal or external leakage of the medium, and easy operation. It effectively solves the problems associated with conventional valves used in chemical pipelines, such as poor corrosion resistance, easy perforation of the casing, and inadequate sealing leading to leaks. It is particularly suitable for transporting chlorine and liquid chlorine in the chemical industry, meeting the requirements for long-term reliable use. Its sealing performance, maintainability, safety, etc. Product features of the AJ45F-25 ammonia stop valve: 1. To address the issues of poor corrosion resistance and easy perforation of conventional valves, this valve designed specifically for ammonia uses corrosion-resistant steel in its construction – carbon steel to which corrosion-resistant alloy elements have been added. It can withstand the corrosion caused by ammonia gas and liquid ammonia, and can operate at temperatures as low as -40°C, thus meeting the requirements of various operating conditions to the greatest extent possible. 2. The sealing pair configuration for valves designed for ammonia uses ball or planar types, enabling automatic sealing compensation and thus providing dual protection. The sealing performance is stable, with no adhesion-related wear, effectively addressing the problem of poor sealing performance and frequent leaks in ordinary valves used in chemical pipelines. 3. The flanges in the product utilize a mortise-and-tenon sealing structure, ensuring absolutely reliable sealing of the middle flanges even in the face of fluctuations in pipeline pressure. 4. The upper sealing device uses multi-layer polytetrafluoroethylene sealing material to create a combined seal, ensuring no leakage of fluid from the packing box during the valve’s service life. This eliminates the problem associated with ordinary valves, where the packing box sealing is weak, allowing fluid to leak out and even leading to accidents. Product standard for AJ45F-25 ammonia stop valve ※An enterprise standard formulated on the basis of GB/T12235 standard. The enterprise standards are formulated entirely based on the corrosion characteristics of chlorine and liquid chlorine, as well as the requirements of operating conditions, in terms of material selection and structural design; all technical parameters meet standards that are superior to those set by national standards. http://www.shylfm.com/pic/20122210315014986.jpg
Why doesn’t the original poster consider using a ball valve? Based on personal experience, ball valves are not as good as globe valves for regulating flow, but they are more reliable in terms of sealing than globe valves. Could it be that the valve core of the stop valve wears out easily, causing internal leakage?
It’s better to use 4F for the sealing surface; those with rigid seals are prone to leakage.
We are an ammonia synthesis plant; for ammonia storage tanks, J41B type ammonia valves are generally used. The pressure is above 4.0 MPa, the valve body is made of cast steel, and the sealing gasket is made of PTFE. Notice on the Incident of Liquid Ammonia Valve Failure (Special Circular from the Quality Inspection Office [2007] No. 258): II. For liquid ammonia valves made of gray cast iron and used in pipelines carrying liquid ammonia as a medium (including pipelines using ammonia as a refrigerant), the allowable nominal pressure shall not exceed 1.0 MPa, and the operating temperature shall not be lower than -10 °C. The entities that use pipelines filled with liquid ammonia shall purchase and use valves for such liquid ammonia in accordance with the aforementioned requirements, and the manufacturers of these valves must strictly follow those requirements by using appropriate materials in their production.