Drill Collar

Drill Collars are one of the parts of a drill’s string. Drill for the Collars is meant to provide weight for drilling purposes. The Drill Collars are thick walled tube like pieces that are machined from solid steel bars, although they are often made from plain carbon steel or the non magnetic alloy of copper and steel or other premium alloys that are non magnetic in nature. Drill collars are mainly used to provide drilling pressure to the drill bit during drilling, so that the drill pipe is in a tensile state, and with its greater rigidity, it can straighten the drill bit and maintain the borehole trajectory. Spiral drill collars and non-magnetic drill collars are special drill collars. Spiral drill collars are made by machining three spiral grooves on the cylindrical surface of the drill collar to reduce the contact area with the well wall. Spiral drill collars can effectively prevent pressure difference and drill sticking. Non-magnetic drill collars are mainly used for monitoring during oil drilling.

Drill Collar Performance Specifications

Spiral Grooving
To avoid differential pressure sticking, the surface of the Drill Collar can be spiral grooved, typically with three right hand spirals.
Drill Collar cross sections shown below show the reduced contact area with the wall of the hole.

SPIRAL GROOVED DRILL COLLAR SPECIFICATIONS
Size O.D.	Depth of Cut	Spirals	Direction	Pitch	Type
41/2 - 51/8	7/32 ± 1/32	3	R.H.	38 ± 1	A
57/8 - 63/8	9/32 ± 1/16	3	R.H.	42 ± 1	A
61/2 - 67/8	5/16 ± 1/16	3	R.H.	46 ± 1	A
7	5/16 ± 1/16	3	R.H.	64 ± 1	A
71/8 - 77/8	11/32 ± 1/16	3	R.H.	64 ± 1	B
8 - 87/8	3/8 ± 1/16	3	R.H.	68 ± 1	B
9 - 97/8	13/32 ± 3/32	3	R.H.	72 ± 1	B
10 - 103/8	7/16 ± 3/32	3	R.H.	76 ± 1	B
11 - 12	15/32 ± 3/32	3	R.H.	80 ± 1	B

Hardbanding
Applied by the metal arc gas shielded consumable electrode process, incorporating granular tungsten carbide, fed automatically into the molten weld pool to obtain uniform distribution.
Precisely controlled pre-heating interpass and post weld heat treatment ensure that only weld overlays of optimum integrity are applied. The deposit is made flush to + 1/32 above the O.D. of the collar.

Stress Relief Features
Downhole tools subject to bending and subsequently cyclic fatigue have been shown to have their connections mechanical characteristics improved by the application of A.P.I. Stress Relief Grooves and Bore Backs. As shown in the illustration below Bore Backs and Stress Relief Grooves are machined in accordance with A.P.I. Specification (Latest Edition).

STRESS RELIEF GROOVE FOR CONNECTIONS
Number or Size and Style ofConnection	Length,Shoulder Face to Groove of Box Member, Tol. +0, -1/8 LX	Diameter of Pin Member at Groove, Tol. +0, -1/32 DRG
NC44	41/8	43/16
NC46 (4 IF)	41/8	421/64
NC50 (41/2 IF)	41/8	43/4
NC56	45/8	519/64
NC61	51/8	555/64
NC70	55/8	647/64
NC77	61/8	727/64
41/2 FH	35/8	415/64
51/2 REG	43/8	455/64
65/8 REG	45/8	527/64
75/8 REG	47/8	613/32

Sizes Of Drill Collar

Drill Collars are available in lengths of 5, 10, 15,
20, 30, 31 and 32 feet and in nominal sizes ranging from 3½” to 14”.

Common sizes are listed here. Other sizes are available upon request.

DRILL COLLAR SPECIFICATIONS
SIZE O.D INS.	BORE		CONNE	CTION STYLE AND		SIZE	APPROX WEIGHT (30FT LONG) LB.	APPROX WEIGHT (3FT LONG) LB.
	Standard Ins.	Optional Ins.	Standard Bore		Optional Bore
	Standard Ins.	Optional Ins.	A.P.I.	No. Other	A.P.I.	No. Other
3½	1½		NC26	2⅜ IF	NC26	2⅜ IF	1012	1045
4⅛	2	1¾	NC31	2⅞ IF	NC31	2⅞ IF	1045	1078
4¼	2	1¾	NC31	2⅞ IF	NC31	2⅞ IF	1122	1155
4½	2	1¾	NC31	2⅞ IF	NC31	2⅞ IF	1298	1342
4¾	2¼	2¼	NC35		NC38	3½ IF	1412	1463
5	2¼	2	NC38	3½ IF	NC38	3½ IF	1606	1659
5¼	2¼	2	NC38	3½ IF	NC38	3½ IF	1793	1848
5½	2¼	2	NC38	3½ IF	NC38	3½ IF	2046	2112
5¾	2¼	213/16	NC40	4 FH	4½ FH		2253	2328
6	2¼	213/16	NC44		NC40	4½ FH	2486	2570
6¼	2¼	213/16	NC46	4 IF	NC46	4 IF	2728	2816
6½	2¼	213/16	NC46	4 IF	NC50	4½ IF	2761	2851
6¾	2¼	213/16	NC46	4 IF	NC50	4½ IF	3025	3124
7	213/16	2¼	NC50	4½ IF	NC50	4½ IF	3304	3412
7¼	213/16	3	NC50	4½ IF	5½ FH		3586	3705
7½	213/16	2¾	NC50	4½ IF	5½ REG		3885	4013
7¾	213/16	3	NC56	6⅝ REG	NC56	6⅝ REG	4191	4327
8	213/16	3	NC56	6⅝ REG	NC56	6⅝ REG	4514	4653
8¼	213/16	3	6⅝ REG		6⅝ REG		4840	4990
8½	213/16	3	6⅝ REG		6⅝ REG		5181	5337
8¾	213/16	3	6⅝ REG		6⅝ REG		5416	5577
9	3	213/16	NC61	7⅝ REG	NC61	7⅝ REG	5786	5973
9¼	3	213/16	NC61	7⅝ REG	NC61	7⅝ REG	6182	6369
9½	3	213/16	7⅝ REG		7⅝ REG		6538	6750
9¾	3	213/16	NC70	7⅝ REG	NC70	7⅝ REG	6930	7154
10	3	213/16	NC70	8⅝ REG	NC70	8⅝ REG	7260	7480
11	3	213/16	NC77	8⅝ REG	NC77	8⅝ REG	9020	9295
11¼	3	213/16	NC77	8⅝ REG	NC77	8⅝ REG	9460	9768
12	3	213/16	NC77	8⅝ REG	NC77	8⅝ REG	10868	11187
14	3	213/16	NC77	8⅝ REG	NC77	8⅝ REG	14949	15400
With 2 ends 11¼ O.D.

Drill Collar Material And Manufacturing Process

Drill collars are available in standard lengths of 30 or 31 feet and are classified into smooth and spiral drill collars, depending on the surface treatment process. Smooth drill collars are rolled to give them a high-quality finish. Spiral drill collars have grooves on the outer surface to promote even flow of drilling fluid around the drill collar, thereby balancing pressure during drilling and reducing differential adhesion between the drill collar and the well wall.

The drill collar material is modified AISI 4145H steel and is supplied in a rolled surface finish. The material is drilled and punched and manufactured in strict accordance with API Spec. 7-1. In order to ensure that the mechanical properties meet or exceed the API standard, the drill collar is heat treated throughout its length, and the hardness range of 1 inch below the surface is controlled to 285-341 Brinell hardness, and the minimum impact strength of the Charpy "V" notch at 70°F reaches 40 foot pounds.

Types Of Drill Collars

The drill collar is located at the bottom of the drill string and is the main component of the lower drill assembly. Its main features are large wall thickness (generally 38~53mm, equivalent to 4~6 times the wall thickness of the drill pipe), with greater gravity and rigidity. Drill collars are generally divided into three types: spiral drill collars, non-magnetic drill collars, and integral drill collars.

The spiral drill collar is a special drill collar among drill collars. The spiral drill collar is processed with three or nine right-hand spiral grooves on the cylindrical surface of the integral drill collar to reduce the contact area and rotation resistance of the well wall. The spiral drill collar can effectively prevent pressure difference and stuck drill. Improve drilling efficiency and drilling safety, the specifications and dimensions are the same as ordinary drill collars.

The non-magnetic drill collar is made of a low-carbon high-chromium manganese alloy steel. It is refined after strict chemical composition ratio and forged to achieve its mechanical properties. It has good low magnetic permeability, high-strength mechanical properties, excellent intergranular corrosion cracking resistance and excellent wear resistance. When the magnetic field strength is 1×105/4π A/m, the relative magnetic permeability μr of the non-magnetic drill collar is ≤1.010.

The integral drill collar is a smooth thick-walled round tube with threaded connections at both ends. The integral drill collar is a common and important type of drill collar. It is forged from a single high-strength steel, and the entire structure has no welding or other connection parts, so it is called an "integral" drill collar.

Drill Collars

Drill Collar Connection Features

Phosphate Coating

To improve the anti-seizure capability of the drill collar connection, all connection parts are phosphate coated.

Stress Relief

API pin stress relief groove and API box shaft back hole design can effectively reduce the frequency of fatigue failure. These stress relief features are processed according to API Spec. 7-2 standard, which significantly improves the flexibility of the connection and reduces the high stress concentration that usually occurs near the end of the meshing thread.

Cold Rolling

The thread root of the drill collar is cold rolled. This process can form a compressive stress state at the root of the thread, thereby minimizing the occurrence of cracks and extending the fatigue life of the drill collar.

Our drill collar joints are manufactured strictly according to API Spec. 7/7-1 standard dimensions and follow the relevant guidelines in API RP7G.

The drill collar connections we provide meet the requirements of API Spec. 7-2 standard, including conventional connections, NC connections, H90 connections and PAC connections. In addition, other types of connections can be provided according to customer specific needs. All drill collars are strictly inspected before leaving the factory to ensure that they meet API standards and Grant Prideco specifications. These inspections include visual dimensional inspections and ultrasonic inspections of the entire length to ensure that each drill collar has high-quality performance.