1. Size and type
Non-magnetic drill collars may be produced as string-type collars or as bottom-hole-type collars.
String-type non-magnetic drill collars shall be furnished with box-up and pin-down connections in the sizes and styles stipulated for the OD and ID combinations listed in Table 14 or Table 20. The connections shall conform to the dimensional and gauging requirements of API Spec 7.
Bottom-hole non-magnetic drill collars shall be furnished with upper box connections in the sizes and styles stipulated for the OD and ID combinations listed in Table 14 or Table 20 and with lower box connections as listed in Table 19. Both the upper and lower connections shall conform to the dimensional and gauging requirements of API Spec 7.
2. Surface finish
Non-magnetic bars and tubes shall have the outside surface machine-turned or ground to 100 % clean-up. Surface imperfection removal shall comply with Table 16.
3 Dimensional requirements
3.1 Length tolerance
The length tolerance for non-magnetic drill collars shall be +652 mm (+6 in).
3.2 Bore eccentricity
The maximum bore eccentricity shall be 2,39 mm (0.094 in) at the collar ends. The centre eccentricity shall not exceed 6,35 mm (0.250 in).
NOTE The purpose of the eccentricity specification in the centre of a non-magnetic collar is to ensure reasonably accurate alignment of a survey instrument with the drill collar axis. Eccentricity in the centre does not have a significant effect on the torsional or tensile strength of the collar.
4. Mechanical properties
4.1 Tensile requirements
The tensile properties of non-magnetic drill collars shall comply with the requirements of Table 18.
These properties shall be verified by performing a tensile test on one specimen (with properties representative of the end product) for each bar size per heat per heat-treatment lot.
Tensile properties shall be determined by tests on cylindrical specimens conforming to the requirements of ISO 6892, 0,2 % offset method.
NOTE For the purposes of this provision, ASTM A 370 is equivalent to ISO 6892.
The tensile specimen may be taken from either end of the bar or tube. The specimen shall be machined so that the centre point of the gauge area is located a minimum of 100 mm (4 in) from the end of the bar or tube. The tensile specimen shall be oriented in the longitudinal direction with the centreline of the specimen located 25,4 mm (1 in) from the outside surface or mid-wall, whichever is closer to the outside surface.
4.2 Hardness requirements
In addition, a hardness test shall be performed on each drill collar for information only. Correlation between hardness and material strength is not reliable. The hardness test shall be made on the outside diameter of the drill collar (Brinell hardness in accordance with ISO 6506-1 is preferred although Rockwell C hardness is an acceptable alternative).
NOTE For the purposes of this provision, ASTM A 370 is equivalent to ISO 6506-1.
