Updated July 22, 2026 · By Drillstrings Technical Team
Choosing a drill pipe grade is one of the most consequential decisions in drill-string design. The grade sets how much tension, torque and pressure a given size of pipe can safely carry — which in turn determines how deep you can drill, how much torque you can apply, and what safety margins you keep. This guide explains the standard API grades and how to choose between them.
What “grade” actually means
A drill pipe grade describes the minimum yield strength of the steel, expressed in thousands of pounds per square inch (ksi). The letter identifies the grade family and the number is the minimum yield strength:
- E-75 — 75,000 psi minimum yield
- X-95 — 95,000 psi minimum yield
- G-105 — 105,000 psi minimum yield
- S-135 — 135,000 psi minimum yield
Grade is independent of size (outside diameter) and nominal weight (which reflects wall thickness). A 5” 19.50 lb/ft tube can be supplied in E-75, X-95, G-105 or S-135; the higher the grade, the higher its tensile, torsional and pressure ratings.
The four standard grades in practice
E-75
The baseline grade, suited to shallow and moderate-depth wells with modest loads. E-75 is economical and widely available, but its lower yield strength limits hook load and torque capacity.
X-95 and G-105
Intermediate grades that add meaningful capacity for deeper wells and higher torque without jumping to the highest strength. G-105 in particular is a common choice for directional and workover drilling where extra margin is needed.
S-135
The high-strength standard for deep, high-torque, extended-reach and offshore wells. S-135 is the most common grade for modern horizontal drilling because long laterals demand high torque and tension capacity. Most 5” and 5½” rental strings for unconventional work are S-135.
How grade translates into capacity
Yield strength is not the rating you drill with — it is the input to the ratings you do. For a given size and wall, tensile capacity scales roughly with cross-sectional area times yield, and torsional capacity scales with the section modulus times yield. Doubling from E-75 to S-135 (1.8× the yield) gives you close to 1.8× the tensile and torsional capacity in the same tube. That is why a long, high-torque lateral that would twist off in E-75 runs comfortably in S-135: the same geometry, a stronger steel.
Two other ratings matter and behave differently. Collapse and internal-pressure (burst) ratings depend on wall thickness and diameter as well as grade, so a higher grade helps but a heavier nominal weight (thicker wall) helps more. And fatigue — the slow accumulation of cyclic damage at the tool joints — is barely improved by grade at all; it is governed by dogleg severity, rotating hours and connection condition. A common mistake is to reach for a higher grade to solve a fatigue problem that actually calls for lower dogleg, better inspection, or a premium connection.
Grade and the connection
Grade sets the tube body’s capacity, but the tool joint is a separate design. A high-grade tube is wasted if its connection cannot carry the same torque. Standard API rotary-shouldered connections (NC38, NC46, NC50 and the FH series) suit most drilling; premium double-shoulder connections add torsional capacity and fatigue resistance for high-torque laterals by adding a secondary shoulder that shares the load. When you specify grade, specify the connection alongside it — the string is only as strong as the weaker of the two.
How to choose a grade
Base grade selection on an engineered drill-string design that accounts for:
- Hook load / tension — the buoyed weight of the string plus overpull margins.
- Torque — especially in long laterals and high-friction holes.
- Collapse and internal pressure — relevant in deep and high-pressure wells.
- Fatigue — dogleg severity and rotating hours drive fatigue at connections.
- Sour service — H2S environments may cap the usable strength and require NACE MR0175-compliant material, which can favor controlled-yield grades.
For a quick orientation: shallow vertical wells often run E-75 or X-95; directional and deeper wells lean on G-105; and deep, high-torque or horizontal wells run S-135. This is only a starting point — see how to select drilling tubulars and drill string design fundamentals for the full method.
Grade, inspection class and remaining wall
A grade rating assumes full wall. Used rental pipe has some wall loss from wear and corrosion, so the real capacity of a joint depends on both its grade and its inspection class. DS-1 and API RP 7G-2 define these classes by remaining wall: Premium class requires at least 80% of nominal wall, and Class 2 at least 70%. A Class 2 S-135 joint and a Premium X-95 joint can end up with similar usable capacity — which is why grade and class must be specified together. For high-torque S-135 laterals, ask for Premium-class pipe; a shallow vertical hole may run economically on Class 2. Always have connections gauged and shoulders inspected too, since fatigue failures start there, not in the body.
Sour service and grade limits
In H2S environments, higher is not always better. Very high-strength steels are more susceptible to sulfide stress cracking, so NACE MR0175 may cap the usable yield or require controlled-yield, qualified material rather than the highest plain grade. In practice this can favor a grade like G-105 in a qualified sour variant over a standard S-135. Where a well is sour, the material specification — not just the grade number — governs, and every tube and connection in the string must comply.
Grade and rentals
When you rent drill pipe, specify size, nominal weight, grade, connection and inspection class together — they define the pipe’s real capacity. Our rental fleet spans drill pipe in all four grades with API and premium connections.
Not sure which grade your program needs? Send us your well parameters and we’ll help you match grade, weight and connection to the job.