Understanding wall thickness in drill pipe, and the detriment of over sizing.

As a case study for understanding wall thickness, we’ll use a Vermeer 100×120 compatible drill rod to demonstrate the importance of having a proper wall thickness on the tube body. The differences of a regular wall (0.368″) vs a heavy wall (0.449″) 100×120 HDD drill rod are:

Weight per rod
Performance
Maximum pull/push force, and of course…
Cost.

Weight per rod:

The additional metal will add about 15% weight to your rack. A heavier drill string in vertical drilling is beneficial, because it adds weight on the drill bit and makes drilling faster. However, in horizontal drilling, the extra weight only increases the friction between the rods and the bottom wall of the hole, thus increasing wear and power requirements. Additionally, the heavier rod is now adding to the total pull back your machine must contend with. The difference in weight between a heavy wall string and a regular wall string is 3200 lbs (100 piece string). Or, another way to look at this is that you could have an extra 14 pieces (280 ft) of regular wall pipe in the ground for that same weight.

Performance:

The inside diameter (ID) of a heavier wall rod is smaller, thus the cross-sectional area is smaller and mud flow is reduced. If you maintain your flow rate your fluid velocity will increase, due to a smaller orifice. The bend radius (207 ft, with 7% safety factor) is unaffected by changing the wall thickness. Bend radius is a mathematical function of the outside diameter (OD), and since the OD is unchanged on a thicker walled pipe, bending radius is neither increased nor decreased as a result of a thicker wall.

The maximum torque capacity of a heavy walled pipe vs. regular wall is irrelevant. The tool joints on the drill stem are always an order of magnitude weaker than the tube body itself when properly heat treated and free from defects. In this case the tool joints have a torque capacity of 23,150 ft-lbf, with no safety factor, and a make-up torque rating of 13,900 ft-lbf. These values are unaffected by using a heavier wall because the torque ratings are dependent on the shoulders and threads of the machined connection. In other words, if someone wanted to over-torque a drill string to break a tube body, the amount of torque needed to do so, would break the threaded connection long before reaching the yield point of the tube body.

Bending fatigue life of the string is also unaffected by the heavier wall. As discussed with torque capacity, a majority of fatigue is seen in the tool joint, not the tube body. Bending fatigue life for the tube body is increased by a proper heat treat and not the wall thickness. S135 creates a higher threshold for fatigue over P110. It’s for this reason that we heat treat all of our tube bodies and tool joints to S135 (135,000 lbs yield) instead of P110 (110,000 lbs yield).

Maximum push/pull force:

The push/pull capacity is higher for a heavier wall. 580,000 lbf force vs 490,000 lbf force over the 0.368″ wall. This value is called Yield Strength (yield meaning permanent deformation) and is a measurement of the steel’s resistance to deformation without any safety factor. The heavier wall string is 18% stronger in push/pull, than the regular wall. This increase in push/pull strength is the only advantage of the heavier wall… However… Adding an extra 100,000 lbf to the string’s push/pull isn’t the advantage it appears to be. The 0.368” wall pipe is already 5 times stronger than the maximum rated capacity of a Vermeer D100x120 machine (rated at 100,000 lbs pull-back). So, is it absolutely necessary to have a tube body which is 480,000 pounds stronger than a machine, when 390,000 (0.368” WT) pounds stronger is still overkill, and has the benefits of less wear, less power needed to drill with, and better fluid flow? .

Cost:

Steel is purchased in bulk, and by the ton. Knowing now that a heavy wall drill string is 15% heavier, that increase in weight/cost is passed on to you, with no real benefit to the drilling operation. The real reason heavy wall drill pipe is produced for HDD is a simple one… manufacturing. The heavy wall pipe is needed in the forging process to create the mass of steel needed to thread the connection at a better cost per piece. Using a regular wall would incur greater processing costs to those manufacturers who make one-piece forged products. In other words, those manufacturers who make one-piece heavy wall pipe are making their lives easier, not necessarily yours.

At Premier Drill Products, we use the right sized tube body and American Petroleum Institute (API) guidelines to create a product that meets the stringent standards for oilfield drill pipe, for use in HDD. No one drilling in the oil patch would send a one-piece drill pipe 30,000 ft below the ground. Which is why every piece of oilfield drill pipe in North America is Inertia Welded, and regulated by API. Inertia welding done by API standards produces an exceptional product with high tolerances. Premier Drill Products produced one-piece drill rods early in our history. In the end, though, we changed to an all Inertia Welded product for the simple reason of the product’s superiority over one-piece forged rods. Now, at Premier Drill Products, the only thing we forge is the weld area for the inertia weld.

Tejas Tubular, Premier Drill Products’ parent company, is an API certified mill. This is our greatest advantage, and the largest benefit to the HDD driller. Tejas and Premier have the purchasing power to acquire steel tubulars and bar stock at costs that most others can’t achieve. Therefore our reduced overhead on raw materials is the first place we save you money. Our manufacturing process is streamlined and highly efficient, which decreases our manufacturing costs, saving you money. Our 26 years of creating API tubular goods translates into every quality piece that comes off the manufacturing line. And, we manufacture all our drill pipe in-house, something no other major manufacturer can say! We heat treat, forge, inertia weld, normalize, machine, inspect, and design in Texas.

Premier Drill Products offers great value, the best warranty in the industry, exceptional quality, and excellent customer service. Give us a call and you’ll see why we say: Any Machine, Any Ground Anywhere.