Discussion on the discrepancy in the number of flange bolt holes between GB/T9119 and JB/T81 for DN65
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1. Table 5 of the national standard GB/T9119-2010 specifies that plate-type butt-weld flanges with PN1.6 rating and DN65 size have 8 bolt holes； 2. Table 4 of JB/T81-2015 from the Ministry of Machinery also specifies that plate-type butt-weld flanges with PN1.6 rating and DN65 size have 4 bolt holes ； The two are contradictory. Question: (1) Since both of these are **grade standards, why can’t they be unified? When to use 8 and when to use 4? Is there an official statement? (2) Additionally, regarding flexible rubber joints, Clause 5.7 of the national standard GB/T26121-2010 specifies that the standards for metal flanges should be in accordance with GB/T9119. Can it be understood that when a flexible rubber joint is fitted with a steel flange, a PN1.6 DN65 flange should have 8 holes? Why are DN65 rubber joints with 4-hole steel flanges available on the market? (3) At the construction site, flexible rubber joints with PN1.6 rating, DN65 size, and 8-hole steel flanges were installed together with DN65 ductile iron valves of the same pressure rating and specifications (having 4 bolt holes), and there was no issue with installation ； However, since the ductile iron flange has 4 holes, it was considered that the rubber joint with 8 holes was sent by mistake, and thus the order for the DN65 rubber joint with 8 holes was rejected. Is this approach correct? Experts are welcome to share their opinions or suggestions; please send them to RQSS99@ALIYUN.COM. Thank you.
GB/T denotes recommended standards, whereas GB represents mandatory standards that must be followed. It’s normal for standards to differ; what’s the point of coming up with two standards when a complete citation is already available?
In the old standard 9119, there are 4 bolts, while in the 20592 standard there are 8. The notes specify that 4 bolts can also be used. DN65 is a rather awkward size – it’s neither large nor small; simply indicate how many bolt holes are required when placing the order.