Found in drilling operations everywhere, drill pipes are durable, seamless piping designed to withstand high-pressure, corrosive environments. Within a drill column, this pipe helps circulate essential fluid while also enabling the rotation of the drill bit. Drill pipes are used in various operations, including the extraction of gas, oil, water, and other natural resources. 

Classification and Grades Of Drill Pipes

The most prominent specification for this type of piping is API 5DP. This guide provides essential details for the drill pipes, including

  • Technical delivery conditions
  • Pipe size
  • Pipe weight
  • Pipe grade
  • Pipe material properties. 

Drill Pipe Product Specification Levels

Additionally, API 5DP also has provisions for details like inspection and classification requirements. Manufacturers can refer to this guide to get info on the three product specification levels of drill pipes included below 

PSL-1: Specifies a specific material grade's yield strength, wall thickness, and impact strength requirements.

PSL-2: Additional mandatory requirements.

PSL-3: Additional mandatory requirements.

Drill Pipe Grades

Grades for drill pipes are essential as they help define the product's minimum yield strength. For example, markers like X, G, and S demarcate the thigh-strength capability of the drill pipe. Steel with higher grades has more durability be it in terms of 

  • Yield strength
  • Tensile strength
  • Torsional strength
  • Anti-extrusion strength

High Strength Grades

The most commonly used high-strength steel drill pipe grades under API standards are X - 95, S - 135, and G - 105. These pieces are typically used in projects requiring deeper-service pipes, such as offshore gas and oil fields. In addition, grades X - 95, S - 135, and G - 105 are known for superior yield strength. 

  • X-95: Minimum Yield Strength: 95,000 psi
  • G-105:Minimum Yield Strength: 105,000 psi
  • S-135:Minimum Yield Strength: 135,000 psi 

Mild Strength Grades

Compared to high-strength drill pipes, Grade E drill items are used in more environments. These pipes are generally applied in projects with the well depths ranging from 10,000 to 15,000 feet. Also called "mild" steel, Grade E drill pipes have exhibited a low yield strength per unit area with a yield strength averaging 75,000.

However, the advantage of using this tubular is that they are less prone to weathering and fatigue. Because of this quality, Grade E drill pipes can withstand more strain before cracking compared to higher-grade pipes. 

  • E-75: Minimum Yield Strength: 75,000 psi

Drill Pipe Class

Drill pipe class is generally derived by using a spherometer. This tool helps evaluate the pipes' radius and circumference, enabling sellers to categorize the items based on physical conditions like dimension, corrosion, surface weathering, and more. Following are the three main drill pipe types based on their condition 

Class 1 or Class N: This category of drill pipe consists of brand-new items that have never been used. Class 1 items are, therefore, the strongest of the three classes. 

Class 2 or Class P: For any piece to qualify as a Class 2 pipe, it must have at least 70% remaining body wall (RBW). Despite its slight use, Class P items can be efficiently integrated into drilling columns as drill string components. 

Class 3 or Class C: Drill pipes with extensive wear are classified as Class C. These items are the lowest quality tubular for drilling and typically retain only a limited percentage of their original wall thickness. Once Class C drill pipes become obsolete, they are sold for scraps on the basis of their manufacturing material. 

Drill Pipe Components Based on Design/Construction

Regular Drill Pipes

Regular drill pipes are typically around 30 to 33 feet long, with an OD averaging 4.5 inches. Regular lengths like these are usually used in the upper sections of the drill string. However, in other sections of the drilling components, the following pieces may also be used

Tool Joints

Tool Joints are a critical component of a drill string. Compared to a typical drill pipe, these are conduits designed to connect multiple pieces. A tool joint has special threads at its ends that enable drillers to join multiple pipes. Tubular steel conduits like these may be male or female.

Tool joints are an essential aspect of offshore drilling projects. If reserves are over 15,000 feet deep, these tools help connect the surface portion of the drill string with the bottom hole assembly. Tool joints connect to critical equipment like the drill bit and also enable the movement of the lower pipe assembly. 

Drill Collars

Drill collars play an important role in drilling operations. When boring into a reserve, the drill bit must be subject to adequate pressure and weight. Made from heavy, solid steel alloys, drill collars provide just this. These tools are a part of the drill string's bottom half assembly and help weigh down the drill bit. A drill collar is made of heavy, dense steel and has thicker walls than a standard drill pipe. Aside from providing the necessary weight to the drill bit, these tools also help limit excess vibration and rotational impact. 

Heavy Weight Drill Pipes

HWDP or Heavy Weight Drill Pipes are regularly used as connectors between drill collars and thinner drill pipes due to their flexibility of application. These types of tubular pipes work best as transitional pieces because they are stronger than regular drill pipes. Heavy-duty drill pipes are produced to add weight to the required components in the drill string. 

These pieces are designed to withstand high pressure and can thus bear the fatigue and stress required from connecting components. HWDP has to be thicker than regular drill pipes to handle this pressure. Therefore the diameter of these pipes ranges from 3.5 to 6 ⅝ inches. Since heavyweight drill pipes are used to add weight to the drill string, they are also heavier compared to thinner piping. HWDP thus has a higher pound-per-foot weight, with tensile strengths ranging from 200,000 lbs to 1,000,000 lbs.