In heat exchangers and piping, the removable mechanical connection that joins a tube to a tubesheet or fitting using a compressive ring is commonly called a:

Introduction / Context:
Plant equipment uses various mechanical connections to allow assembly, maintenance, and leak-tight service. In small-bore tubing and some exchanger fittings, a compressive ring component is central to a removable, re-makeable joint.

Given Data / Assumptions:

• Removable (non-welded) tube-to-fitting/tubesheet style connection.
• Uses a compressive ring to grip and seal the tube.
• Common terminology in instrumentation and light-duty exchanger applications.

Concept / Approach:
A “ferrule” is the conical or ring-shaped element that compresses onto the tube under nut tightening, biting into or gripping the outside diameter and creating a metal-to-metal seal. While nipples, sockets, saddles, and spigots are standard pipe terms, they do not describe the compressive ring element that makes the removable seal.

Step-by-Step Solution:
Identify the component: a ring compressed by a nut to seal/lock a tube.Match to naming conventions: “ferrule” is the standard name for the ring in compression fittings.Other listed items are different components (threaded short pipe = nipple; socket = coupling; saddle = support/branch).

Verification / Alternative check:
Compression fittings (single- and double-ferrule types) from major vendors universally use the term “ferrule.”

Why Other Options Are Wrong:
(b), (c), and (d) refer to different hardware; (e) “spigot” is a male end, not the compressive ring.

Common Pitfalls:
Confusing ferrule with the nut; assuming welded tube-to-tubesheet joints are removable—they are not.

Final Answer:
Ferrule