Knowing Your Drill Pipe

Maxi rig HDD contractors are faced with many choices about drill pipe when considering a purchase.  
Among them are these eight considerations: The size of the mid-body tube; the wall thickness(otherwise described as the “weight per foot”); the grade of steel; connection size and type; buying new vs. used pipe and determining the condition of the used pipe; the manufacturer, or source of the pipe; availability or delivery time; and hard band options.

Let’s discuss each of them below as each is important in your decision-making process.

1. Size of the Mid-Body Tube:
There are several reference tables and resources available to show the properties of various sizes of tubes depending on the diameter, wall thickness and grade of steel. Another important consideration that is not commonly discussed is Torsional Stiffness.  This becomes very important while drilling a pilot hole on an extended reach HDD project. For example, 6-5/8 in., 27.70 lbs/ft, S-135 drill pipe, which has a .362-in. wall thickness will have 59 percent less “twist” than 5 in., 19.50 lbs/ft, S-135, which also has a .362-in. wall thickness. This becomes important while trying to maintain “high side” or the clock-face position of the mud motor and drill bit at the end of a 5,000-ft string of pipe.

2. Wall Thickness:
Generally speaking, bigger is stronger. However, it is interesting to note that 5-in., 25.60 lbs/ft, S-135 pipe that has a .500-in. wall thickness is stronger in torsion and tension than 5-1/2 in., 21.90 lbs/ft, S-135 which has a .361-in. wall thickness. However, the torsional stiffness properties of the 5-1/2 in. are better.

3. Grade of Steel:
Most contractors and some engineering firms have determined that S-135 is their preferred grade of drill pipe for maxi rig HDD projects. Modern chemistries of steel used by major drill pipe manufacturers have taken this to a higher standard. The new blends of steel allow for heat treating that makes the pipe “tougher” than found in previous years. The goal is to have the pipe “leak-before break” if a failure is experienced. Other grades of steel such as G-105, which has minimum yield strength of 105,000 psi are primarily manufactured for other applications such as oil and gas drilling where H2S may be encountered.

4. Connections size and type:
Most HDD contractors prefer to use common, field-tested API style connections such as 4-1/2-in. IF, 5-1/2-in. Full Hole, 6-5/8-in. Full Hole or Double Shoulder versions of these connections. These connections are available in their standard form or with a “double shoulder” feature. The double shoulder versions of these connections provide a secondary shoulder at the end of the pin. This adds approximately 30 percent or more strength to the connection and helps prevent over-torque to the connection if downhole make-up torque is experienced.

5. New vs. Used:
Now for the good stuff. Do you want to buy new or used drill pipe? The primary thing to consider is the useful remaining life of used pipe compared to a new pipe. For example, let’s evaluate 6-5/8-in. Full Hole connections on 6-5/8-in., 27.70 lbs/ft S-135 tubes. New pipe can be built with 8-1/2-in. OD tool joints. The minimum OD for this pipe to pass a Premium Class or DS1-CAT5 inspection is 8-in. OD.  New pipe is available for X amount of dollars per foot; therefore, you can calculate the value that you are willing to pay for used pipe based on the remaining useful life before the pipe falls below Premium Class inspection criteria.  
Another very important consideration while evaluating the value of used pipe is the “useable tong space.” This same 6-5/8-in. pipe is typically manufactured with 10-in. Pin Tong Length and 13-in. Box Tong Length.

Some of the tong space may be lost to Hard Banding — since you cannot grip hard banding with the rig vises or jaw dies on tongs. It is important to look at the Useable Tong Length of Pin and Box tool joints when considering buying used pipe. Some pipe may not have enough space to work with certain rig vises.  If there is hard banding on both the Pin and Box tool joints, be sure to see that there is enough area between the hard band surfaces to work on your rig.  For example, if your drilling rig has 5-in. wide vise dies and the distance from the outside of one die to the outside edge of the other die is 14 in., you would not be able to use pipe with 6 in. of useable tong space with hard band on the Pin Tong and Box tong.

6. Pipe Source, aka Manufacturer:
You should consider quality control standards from the manufacturer of new pipe, or inspection standards of used pipe. Modern manufacturing standards have increased the length of the upset on the tube at the weld neck area. The longer transition length will reduce your chances of failure in the field.

7. Availability or Delivery Time:  
Plan your drill pipe purchase to allow for better selection and availability or delivery of new pipe.  Too often a contractor has to make a choice about purchasing pipe that is in stock, ready to ship immediately. In some cases, the contractor may have better selection of pipe, or options such as hard banding if they could wait a week or two to get better pipe.

8. Hard Band Options:
Hard banding can extend the life of drill pipe when used on rock crossings.  Consult with your vendor about the placement and types of hard banding that are available.

There are resources available from your drill pipe vendor or manufacturer to assist with these decisions. T.H. Hill has published inspection criteria that has become an industry standard. Inspection criteria and standards range greatly from Double White Band, API Premium Class, up to DS1-CAT5. Don’t think that all pipe with two white bands meets all of the criteria for Premium Class or DS1-CAT5 inspection.  Those two white bands may just indicate that the Tube meets 80 percent minimum Remaining Body Wall (RBW) criteria.
Your drill pipe vendor or manufacturer should be able to provide reference material, calculations or inspection reports to help you determine which pipe is right for your application.

Jay Miller is president and owner of JT Miller Inc., headquartered in Conroe, Texas.