Problems with double-headed studs

Advantages of double-ended studs over hex head bolts: 1. Double-ended studs have threads on both ends, allowing the length of the threads to be adjusted during installation, which facilitates adjusting the gap between the connected components. 2. Double-ended studs can withstand large axial forces, making them suitable for applications in pipeline systems where high stresses are present. Reasons for eliminating double-headed studs from the current SH3404 and HG20634 standards: 1. Standard updates may be adjusted based on actual application conditions; this might be due to the better versatility and reliability of hex head bolts in practical use. 2. As far as I know, SH3404 and HG20634 are Chinese standards; in the United States, it might be more appropriate to use similar standards from the American standards such as AN, MS, and NAS. When implementing Party A’s plan and using double-ended studs, the following points should be taken into consideration: 1. Material selection: Choose materials with high strength and corrosion resistance that meet the project requirements, such as stainless steel or alloy steel. 2. Thread specification and length: Select the appropriate stud based on the thickness of the connector and the thread specification. 3. Quality inspection: Before purchasing, check the accuracy and integrity of the threads, as well as the material and dimensions of the studs. 4. Installation: During installation, it is important to keep the threads clean to prevent debris from affecting the tightness of the connection ； The threads at both ends must have the same protrusion length to ensure even force distribution. 5. Use anti-loosening measures: For example, employ spring washers, retaining rings, and other such devices during the connection process to ensure a secure fit. .

Double-ended studs are included in the fittings for pressure vessel flanges, while pipe flanges only have bolts and fully threaded studs. Since bolts can only be used for media with a pressure rating of PN16 or lower, and that are non-flammable and non-toxic, it depends on the operating conditions; if bolts are not suitable, fully threaded studs can be used instead.

Double-ended studs have threads at their roots, which can easily become stress weak points. With the advancement of manufacturing techniques and the corresponding updates to American standard thread specifications, double-ended studs have been largely replaced by fully threaded studs, without any increase in cost. Due to habitual reasons, some people still refer to fully threaded studs as double-ended studs, meaning this in contrast to the single-thread design of hex bolts.

I agree with what was said on floor 7: using fully threaded studs in place of double-ended studs will do. I guess that’s what the client intends; most of the equipment in Sinopec’s facilities uses fully threaded studs. It seems that there is stress concentration at the junction of the root and head of the hex head bolt, making it unsuitable for use in high-pressure applications. I remember once, there was a fitting on the pipeline; when it arrived, the housing had hex head bolts, and the quality inspection department noticed this, forcing the design and procurement teams to change it to fully threaded studs

This post was last edited by Clouds of flowing water shine on 2023-11-8 at 11:06. Fully threaded versions are of a specialized grade (referenced as HG PN); we suggested using fully threaded connections, but they insisted on using double-ended types for media such as water and air, claiming that hex-head connections are not commonly used. Q235 and 35# steel are still much cheaper.