EUE vs NUE Tubing Couplings — Upset or Non-Upset Ends

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What the letters describe

EUE and NUE describe how the end of a tubing joint is prepared. In EUE — external upset end — the joint end is the upset (thickened) end form named in the published thread-type list, and the coupling is correspondingly larger in outside diameter. In NUE — non-upset end, also written NU — the thread is cut directly into the plain wall, and the coupling can be smaller. Both forms are standard API practice, both are threaded and gauged to API 5CT and 5B discipline, and both are live options in this factory's coupling family, whose stock size list runs from 1.315 in to 4-1/2 in. Coupling packing is in cartons, wooden cases or pallets, or as agreed. Named stock entries in the family also include BTC and LTC stock couplings alongside J55 casing couplings. A protective coating for the coupling entries is also named in the published text, applied on request where the order states it.

The load side of the decision

A tubing string hangs from its top joint and is worked from its connections, so the loads at the connection are a design case the completion engineer calculates for the chosen end form. EUE's upset is a feature of the form: the end is the thickened form the thread-type list names, and the coupling is correspondingly larger. This site publishes no joint-strength or efficiency comparison between the two forms: which form a string takes is the design's decision, taken against its load and clearance cases. The catalogue's named stock coupling — 2-7/8 in EUE — is an EUE item, which is a stock fact, not a ranking.

The clearance side of the trade

NUE's case is geometric: the form's point is the smaller coupling outside diameter, and clearance is the remainder when that diameter is set against the casing's drift diameter. Special-clearance couplings are also listed in this family, as its reduced-outside-diameter coupling form.

Deciding for a real string

Loads: compute or look up the string's tensile case at the top joint and under pump loads, and check it against the connection the design names. Geometry: the coupling OD, the casing drift figure and every restriction the design names for the string are design figures, stated in the enquiry. Duty cycle: state the pulling frequency in the enquiry together with the finish the specification requires — the family's described finish is phosphating, with magnetic particle inspection and marking to API Spec 5CT, and the catalogue also lists copper-plated couplings in the family. The answers follow the string: a slim or dual completion may answer differently from an open one, correctly. The coupling family's named stock entries include 2-7/8 in EUE couplings held in stock and NU tubing couplings, and the family's thread dimensions and tolerances follow API Spec 5CT and 5B. The tubing sizes named in the catalogue run 1.05, 1.315, 1.66, 2.063, 2-3/8, 2-7/8 and 3-1/2 in. The published end-form vocabulary is the thread-type list's: NUE, EUE and the special-clearance form. The published coupling stock sizes run 1.315, 1.66, 1.9, 2-3/8, 2-7/8, 3-1/2, 4 and 4-1/2 in.

Ordering without ambiguity

The failure mode in this comparison is vocabulary. Tubing couplings alone does not specify a form; 2-7/8 couplings alone does not specify a form; and an order history that says couplings as ordered last time breaks the moment the fleet standard changes. Write the form into every line — 2-7/8 in, L80, EUE — and require the quotation to restate it. The catalogue names both forms in the coupling family: the EUE form carries its own stock anchor, and NU is named as its own coupling entry. However you buy, buy the form by name.

Two scenarios that teach the trade

Consider two specification scenarios. If a string turns out heavier or more frequently worked than its design assumed, the loads and the pulling frequency the design stated no longer describe the string, and the form question has to be reopened with the design office on the corrected figures. This page publishes no service-life prediction for either form in that case, and draws no pattern of wear from an over-design case. In a slim completion the clearance question is the same arithmetic from the other side: the coupling outside diameter is set against the casing's drift diameter, and the clearance is the remainder. Both are specification questions: the trade is quantifiable at design stage, and it is decided by the loads and diameters the design states.

The published thread-type list also names a third form for the tubing side: the special-clearance coupling, the family's reduced-outside-diameter coupling form. The list names the form; which form a string takes is the design's statement for that string. Where a design names the special-clearance form, raise it explicitly in the enquiry: it should be quoted as itself, not approximated by turning down a standard coupling as an improvisation. The catalogue names special-clearance couplings in multiple entries, including a J55 tubing coupling entry described as a stock item.

Whichever form your design names for a size, state it on each enquiry line for that size — spares, pup joint and workover lines included — so the quotation confirms the named form line by line. The company's casing literature states that casing and tubing pup joints of various sizes can be machined to order.

Is one end form stronger than the other?

This site publishes no strength comparison between end forms. The upset is the thickened end form the name describes — that is a fact of the form. Whether a given string takes EUE or NUE is confirmed specification by specification, against the design's load and clearance cases.

Can a fleet standardise on NUE to save money?

This site publishes no price comparison between end forms. A fleet standard follows the completion design — the loads and clearance the design states — not a purchasing default: the form is named on every line, as the ordering section above sets out.