Metal gasket for hand hole

The HG/T 20514 standards for manholes and handholes are based on the HG/T 20592–20635 series of standards; the selection of flanges, gaskets, and bolts is carefully matched. As mentioned by the poster, when using HG/T 20530 handholes and metal wound gaskets, this is not appropriate. Please refer to the screenshot: The screenshot is taken from HG/T 20614-2009. The selection of flanges, gaskets, and fasteners should be done in a cost-effective manner.

You’re welcome; let’s learn from each other and improve together.

Hello, I went back and checked 20614 again – it’s on the page right after the one in your screenshot, in the gasket selection table. It says that winding gaskets can be used with SO flanges; isn’t this a bit contradictory from a standard perspective?

This post was last edited by Douwan on 2017-11-13 at 14:44. This is not contradictory. The screenshot in the post refers to the use of flanges with a rating of PN16 or lower, along with metal wound gaskets, etc.; the subsequent screenshot shows the selection of gaskets, and the pressure ratings for the metal wound gaskets listed in the table range from PN16 to 160 (i.e., higher than PN16). In other words, generally speaking, when the pressure is less than or equal to PN16, non-metallic gaskets are usually suitable; whereas when the pressure is greater than PN16, semi-metallic or metallic gaskets are appropriate. You might ask why, for flanges where a metal wound gasket is used and the pressure is ≤ PN16, WN flanges are recommended, while for PN25 flanges, SO flanges can be used with metal wound gaskets This is because pipe flange standards are part of a series of standards, and the underlying principle is versatility. The original poster might want to take a look at small flanges with a pressure rating lower than PN16 (such as DN25, DN50, etc.); although their pressure ratings differ, their dimensions remain the same. This is because the flange is small, the stress is low, and the material is lightweight; there’s no need for such fine distinctions. Therefore, for market versatility, they are all made to the same size, as they all meet the requirements for strength calculations. For pressures higher than PN16, the flange dimensions change due to differences in pressure ratings. In other words, for pressure levels below PN16, SO flanges may not be able to meet the pre-tensioning requirements of metal or semi-metal gaskets (due to limitations in flange size and insufficient stiffness). At pressures above PN16, however, the increase in pressure leads to an increase in flange dimensions, which in turn results in a significant improvement in the flange’s stiffness (as its thickness increases). Therefore, the standards require that when the flange rating is ≤ PN16, WN flanges should be used, primarily to ensure sufficient flange stiffness.

Perhaps the standard wording isn’t clear enough; I always feel that the range of 16–160 should include 16, as PN16 WN flanges can definitely be used with gaskets. So, according to the author’s intention, 16 is indeed included in this range. However, point 9 mentioned earlier states something different. It would be clearer if this information could be included in the notes at the bottom of the table.

There’s no need to stick strictly to the exact wording; understanding the intention is enough. Such regulations and standards are merely suggestions, not mandatory. If you really want to use SO flanges plus wound gaskets, it’s not necessarily impossible. As a designer, you first need to have your own judgment (the distinction between reasonable and more reasonable), rather than focusing on what is correct or incorrect.

Basically, a senior colleague told us a story about a situation where the equipment designed for the client leaked, and efforts were made to find out the cause. The gaskets chosen at that time seemed fine, but since there were no standards or guidelines to refer to, the client tried to shift the blame onto us. We suspected that there might have been problems during manufacturing or installation, but it was difficult to prove that the fault lay with us. So even if we knew everything was fine, we still needed solid evidence before we could use those gaskets

See above, forgot to reply. . This time, I’m worried that if I choose SO paired with a wrapping pad and something goes wrong, it might turn into my problem even though it’s not my fault

I have said a lot, and I made it very clear. I also tried my best to answer your questions. As for how you do it, that’s up to you to decide. You want to use gasketing material, and at the same time you want to find out where to get it; the standards clearly recommend using WN. I’m really at a loss here.