By Colin Rice
How are drill rods and drillpipe manufactured, and which grades of steel are used?
This is the third in a series of articles on drill rod manufacturing, and is Part 1 of our Technical Series on Drill Rod Safety. In the previous article, we covered how drill rod tubes are manufactured and the strength characteristics of the steel tubes, and the first article considered the forces and stresses in drill rods. In this article we look at the different ways that drill rods and drillpipe are manufactured, and the grades of steel that are used. Click here for an outline of the entire Technical Series on Drill Rod Safety.
Methods of manufacture of drill rods and drillpipe
Firstly, let us clarify the difference between drill rod and drillpipe.
Drill rods are manufactured by cutting a pin and a box thread directly onto the steel tube – the drill rod is therefore a one-piece construction. All standard wireline drill rod is manufactured in this way.
Drillpipe is a composite construction and is manufactured by welding tools joints onto the end of a tubular mid-body. Drillpipe is therefore a three-piece construction.
All drillpipe used in oil and gas exploration and all rotary percussion and dual-tube reverse circulation drillpipe is manufactured in this way. A range of heavy-duty diamond drill rods are also manufactured in this way.
The tool-joints can be welded to the mid-body in a number of different ways but the two most common are butt-welding and friction welding. We won't be discussing the different welding techniques in this article, but if you're interested in hearing more on welding techniques, please leave us a comment or question at the end of this article.
Grades of steel commonly used in manufacture of drill rod and drillpipe
Until relatively recently, steel mills manufactured only a few grades of steel that were used in the manufacture of drill rod and drillpipe. The most common grade used in the manufacture of diamond core drill rods was what is called SAE 1541 material – this tubing has a Yield Strength of about 620 MPa and a UTS of about 700 MPa.
A lower grade tube, with a Yield Strength of 550 MPa and a UTS of 620 MPa is commonly used to manufacture casing, outer-tubes and inner-tubes.
In recent years, a range of higher strength alloys with Yield strengths of up to 900 MPa have been used to increase the depth capacity of wireline core drill rods.