Upset: Internal and External Forging of Tubular Ends, EUE Versus NUE Connections, and Tool Joint Weld Strength in WCSB Wells

An upset is the thickened, reinforced section forged at the end of a tubular such as drillpipe, casing, or production tubing, where extra wall thickness and outside diameter are added to compensate for the metal that will be removed when threads are cut or to provide a stronger base for welding a tool joint. When a thread is machined into the end of a plain pipe, it cuts into the wall and weakens the cross-section precisely where the connection must carry tension, torsion, and pressure. Upsetting solves this by hot-forging the pipe end so the steel is locally thicker before the thread is cut, restoring or exceeding the strength of the pipe body at the joint. The forging is done by heating the pipe end and pressing it in a die, displacing metal to increase wall thickness without adding a separate sleeve. There are three geometries. An internal upset, or IU, thickens the wall inward so the outside diameter stays flush while the bore narrows at the end. An external upset, or EU, thickens the wall outward so the bore stays constant while the outside diameter swells. An internal-external upset, or IEU, thickens both directions to obtain the greatest possible wall for a high-strength connection. For drillpipe, the upset provides the robust shoulder onto which a tool joint is friction- or flash-welded; today most drillpipe tube ends are internally and externally upset to give the thickest cross-section for that weld. For production tubing the same idea produces two of the most common API connection families: external-upset-end, or EUE, tubing has an enlarged outside diameter and is the workhorse of WCSB completions because the upset restores full pipe-body joint strength, while non-upset-end, or NUE, tubing has no thickening and therefore a substantially weaker connection that is used only in low-load service. The American Petroleum Institute, through specifications such as API 5CT for casing and tubing and API 5DP for drillpipe, sets the dimensional and metallurgical requirements for upsets on every size and grade. The upset connects directly to the concepts of the tool joint, the drillpipe body, the casing string, and the broader category of OCTG tubular goods, and it is one of the quiet design details that determines whether a string survives the tension and cyclic fatigue of a deep WCSB horizontal.

Internal, External, and Internal-External Geometries

The choice among IU, EU, and IEU upsets is a trade between flush bore and flush outside diameter. An internal upset keeps the OD constant, which matters when the pipe must pass through a tight casing clearance, but it narrows the drift at the connection. An external upset keeps the bore constant, preserving flow area and the ability to pass tools, but the enlarged OD reduces annular clearance. An internal-external upset compromises on both to maximize wall thickness, which is why it dominates high-strength drillpipe. On WCSB tubing, EUE is favoured because the external swell restores joint strength while the bore stays full for rod pumps, plungers, and intervention tools, even though the larger OD slightly reduces casing annulus space.

Forging Process and Fatigue Performance

Upsets are formed by induction or furnace heating the pipe end to forging temperature, then pressing it in a series of dies that displace metal to build the thicker section over a tapered transition back to the pipe body. That taper, sometimes called the upset runout, is a critical fatigue feature: an abrupt change in wall acts as a stress raiser, so API limits the taper geometry to spread bending stress smoothly. In cyclic service such as the rotating bending a drillpipe sees in a high dogleg WCSB horizontal, fatigue cracks tend to initiate at the upset transition or in the tool-joint weld zone. Proper upset taper, heat treatment, and weld quality therefore directly govern drillstring life and the inspection interval for the string.

Related Terms

The upset exists to serve the tool joint, the heavy threaded box and pin welded onto each end of a joint of drillpipe; the upset is the thickened weld base that makes that connection reliable. The same upsetting logic applies across OCTG goods, including casing strings, where connection strength must match the pipe body to survive running loads and pressure testing. Understanding the upset clarifies why some tubing is sold as EUE and some as NUE and why that single letter of difference changes the safe tension rating of an entire completion string.

Real-World WCSB Scenario: Drillstring Selection for a Deep Montney Horizontal

An operator planning a 4,200 m measured-depth Montney horizontal near Dawson Creek must drill through a build section with dogleg severity approaching 9 degrees per 30 m. The drilling engineer specifies premium-class internal-external upset drillpipe with double-shoulder tool joints rather than reusing older internal-upset stock, accepting a rental premium of roughly 14 CAD per metre, about 59,000 CAD over the string, to gain fatigue margin through the doglegs.

The string completes the well without a twist-off, and post-run inspection finds no fatigue indications at the upset transitions. A nearby offset that ran lighter, single-shoulder pipe through a similar build had suffered a washout at an upset runout the prior season, costing about 310,000 CAD in fishing and lost time, validating the heavier upset specification.