Definition
Yield Strength — Yield strength is the stress at which a steel begins to deform permanently rather than elastically, and its minimum value defines a drill pipe grade — 75,000 psi for E-75 up to 135,000 psi for S-135.
Also known as: yield strength, minimum yield, yield point
What yield strength is
Yield strength is the stress a steel can carry before it starts to deform permanently. Below the yield point, load is elastic and the pipe springs back; above it, the metal takes a permanent set. For drill pipe, the minimum yield strength defines the grade — E-75 has a minimum of 75,000 psi, X-95 is 95,000 psi, G-105 is 105,000 psi, and S-135 is 135,000 psi.
Because string design keeps stresses safely below yield, this value — combined with the pipe’s cross-sectional area — sets the maximum allowable tensile pull and, with the polar section modulus, the torsional capacity.
Why it matters
- Load limits — allowable hook load and make-up torque derive from yield strength.
- Safety factor — operators design to a fraction of yield to leave margin for bending and dynamic loads.
- Environment — in sour service, higher-yield steels face NACE MR0175 hardness limits to avoid sulfide stress cracking.
Renting the right grade
Selecting yield strength (grade) balances load capacity against weight and cost. We rent drill pipe across grades from E-75 to S-135 — contact us with your hook load and torque requirements and we will match the grade.