API Tubing Specification

API Tubing is the conduit through which oil and gas are brought from the producing formations to the field surface facilities for processing. Tubing must be adequately strong to resist loads and deformations associated with production and workovers. Further, tubing must be sized to support the expected rates of production of oil and gas. Clearly, tubing that is too small restricts production and subsequent economic performance of the well. Tubing that is too large, however, may have an economic impact beyond the cost of the tubing string itself, because the tubing size will influence the overall casing design of the well.

Tubing transports the oil and gas from deep in the well to the surface – the third phase of the wellbore. Oil and gas occasionally rise to the surface on their own; usually, pumps are needed to bring the fluids to the surface.

API Tubing naturally has a smaller diameter than casing, except for the 4 1/2-inch diameter. An outer diameter of 114.3 mm (4 1/2 inches) is considered a threshold and can be either casing or tubing. Anything smaller is called tubing, anything larger is casing.

Casing and Tubing:

Casing and tubing strings are the main parts of the well construction. All wells drilled for the purpose of oil or gas production (or injecting materials into underground formations) must be cased with material with sufficient strength and functionality.

The outer tubes are called casing pipe. Casing lines the wellbore and thus protects the layers of soil and above all the groundwater from being contaminated by the drilling mud or frac fluids. It also stabilizes the wellbore, so casing must be able to withstand especially high loads. The drilling and casing alternate – the drill string is taken out at specific intervals and the wellbore is lined with casing and cemented. Then drilling continues.

API Tubing Specification & Size Chart:

Outside Diameter		Wall Thickness		Weight				Grade and Upset Type*
				Non-Upset T&C		External Upset T&C
in.	mm	in.	mm	lb/ft	kg/m	lb/ft	kg/m	J55	L80	N80	C90	P110
2-3/8	60.32	0.167	4.24	4.00	5.95	-	-	PN	PN	PN	PN	-
		0.190	4.83	4.60	6.85	4.70	6.99	PNU	PNU	PNU	PNU	PNU
		0.254	6.45	5.80	8.63	5.95	8.85	-	PNU	PNU	PNU	PNU
		0.336	8.53	7.35	10.94	7.45	11.09	PU	-	PU	PU	-
2-7/8	73.02	0.217	5.51	6.40	9.52	6.50	9.67	PNU	PNU	PNU	PNU	PNU
		0.276	7.01	7.80	11.61	7.90	11.76	-	PNU	PNU	PNU	PNU
		0.308	7.82	8.60	12.80	8.70	12.95	-	PNU	PNU	PNU	PNU
		0.340	8.64	9.35	13.91	9.45	14.06	-	PU	-	PU	-
		0.440	11.18	11.50	17.11	-	-	N	PN	-	PN	-
3-1/2	88.90	0.216	5.49	7.70	11.46	-	-	PN	PN	PN	PN	-
		0.254	6.45	9.20	13.69	9.30	13.84	PNU	PNU	PNU	PNU	PNU
		0.289	7.34	10.20	15.19	-	-	PN	PN	PN	PN	-
		0.375	9.52	12.70	18.91	12.95	19.27	-	PNU	PNU	PNU	PNU
4	101.60	0.226	5.74	9.50	14.14	-	-	PN	PN	PN	PN	-
		0.262	6.65	-	-	11.00	16.37	PU	PU	PU	PU	-
4-1/2	114.30	0.271	6.88	12.60	18.75	12.75	18.97	PNU	PNU	PNU	PNU	-

* Premium connections are available on request. P - plain end, N - non-upset, E - external upset.

Read more: OCTG Casing Pipe Size Chart or Seamless Casing vs. ERW Casing