Issues regarding the combination of gasket material and bolt material
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Our company uses polytetrafluoroethylene gaskets for the ammonia pipeline systems it designs, along with A2-70 hexagonal bolts. Based on the reactions at the site, there were leaks in some of the projects. Could it be that the PTFE gaskets were too hard while the bolts were too soft, resulting in poor sealing? If that’s the case, are there any specific requirements regarding the combination of gasket material and bolt material? I checked some chemical engineering design manuals but couldn’t find any relevant information.
Bolts can be made of stainless steel; the main thing to consider is the flange. The PTFE gasket should be in good condition as well
CF8 or WCB is used for flanges.
It could be that the tightening force is insufficient, or the flange selection may be incorrect.
The flange is of the plate-type flat weld type, with the RF face. Insufficient tightening force means the bolts aren’t tightened enough? It is said that there were quite a few leaks at the site; it’s unlikely that they weren’t all tightened properly.
This post was last edited by xlxuiin on 2015-6-3 18:58. What is the ammonia concentration? What size pipe? Tetrafluoroplastic gaskets are soft gaskets with cold flow properties; they tend to deform under excessive tightening, resulting in leaks. It is recommended to replace the gasket. Wrapping gasket
The concentration is around 20%, and the pipes are DN50 and DN65. Can a rubber pad be used then?
This post was last edited by zhangjuhua on 2015-6-3 22:32. Is the pressure high? What is the temperature? A2-70 will also work. Since the flange is made of carbon steel, strictly speaking the expansion coefficients of carbon steel and stainless steel are not identical; it might be advisable to use carbon steel instead, along with metal wound gaskets and increased bolt tightening force. The flange itself could also be replaced with one that has better stiffness for better compatibility, or a seal surface of better quality could be considered – M/FM, TG, RTJ?
PN10 is used, at room temperature. It seems there is no such thing as \"PTFE gaskets not being suitable for A2-70 bolts\"; it’s probably due to other reasons.
Our pipes for ammonia water, ammonia gas, liquid ammonia, etc., are made of carbon steel, use WN flange types with wound gaskets, and 35CrMoA/35# bolts, and no problems have ever occurred
We design our liquid ammonia in this way; since the pressure of ammonia solution is low, we don’t do it that way.