What Is a Drip Ring?
Quick Answer: A drip ring (also called a bleed ring) is a flat, annular metal ring with one or more threaded connections (typically 1/2” or 3/4” NPT) that sits between two pipe flanges. It provides a point to drain, vent, sample, or inject chemicals into a flanged joint without breaking the main flange connection.
Design and Construction
A drip ring is machined from carbon steel, stainless steel, or alloy plate to match the flange bore and bolt circle. It includes a machined groove or channel on its inner face that communicates with the pipe bore, plus one or more radial tapped holes that exit to the outer diameter.
| Feature | Typical Specification |
|---|---|
| Materials | ASTM A105, A182 F304/F316, alloy steel per pipe class |
| Connections | 1/2” or 3/4” NPT (threaded); sometimes socket weld |
| Number of taps | 1, 2, or 4 (depending on application) |
| Thickness | Varies; typically adds 6-12 mm between flanges |
| Gaskets | Requires two gaskets (one on each side of the ring) |
| Flange compatibility | Raised face per ASME B16.5 or B16.47 |
| Stud bolts | Longer stud bolts to accommodate extra thickness |
Applications
Drip rings serve multiple purposes in process piping:
| Application | How the Ring Is Used |
|---|---|
| Draining | Bottom tapped connection drains trapped liquid from the flanged joint |
| Venting | Top connection vents gas or air during filling or hydrostatic testing |
| Sampling | Allows process fluid sampling without opening the flange |
| Chemical injection | Corrosion inhibitor or biocide injection point |
| Pressure testing | Provides isolation test point for hydrostatic or pneumatic tests |
| Leak detection | Monitors for inter-gasket leakage on critical or hazardous services |
Installation Considerations
Because the drip ring adds thickness between flange faces, the standard stud bolts must be replaced with longer ones. Two separate gaskets are required—one between each flange face and the ring. The additional gasket joint introduces a potential leak path, so drip rings should only be specified where functionally required.
Drip Ring vs. Spectacle Blind
A drip ring provides process connections but does not isolate flow. A spectacle blind provides positive isolation by inserting a solid disc into the line. The two serve fundamentally different purposes and should not be confused.
| Feature | Drip Ring | Spectacle Blind |
|---|---|---|
| Primary function | Drain / vent / sample | Positive isolation |
| Flow blocked? | No | Yes (when blind disc is rotated in) |
| Tapped connections | Yes (NPT) | No |
| Added thickness | 6-12 mm | Depends on blind thickness per ASME B16.48 |
Drip rings are specified on the P&ID and included in the material take-off with their associated longer stud bolts and extra gaskets.
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