API 5DP Drill Pipe Grade Selection compares E75, X95, G105 and S135 by strength level, load condition and drill string performance. E75 starts at 75 ksi minimum yield strength, X95 at 95 ksi, G105 at 105 ksi and S135 at 135 ksi, but grade selection should not move upward only because the number is higher. E75 is normally reviewed for moderate tensile and torque demand, X95 for added load margin, G105 for deeper or directional drilling, and S135 for high hook load, long horizontal sections or higher torque conditions. The correct grade should match the full load path, including dogleg severity, fatigue exposure, OD / wall thickness, upset type, tool joint condition, connection capacity and traceable inspection records.
API 5DP Drill Pipe Grades and Mechanical Properties
API 5DP Drill Pipe Grades should be read as the mechanical acceptance baseline for the pipe body, not as a complete drill string selection result. The strength window of each grade needs to be checked together with pipe size, wall thickness, upset geometry, weld zone, tool joint configuration, connection type, hardness / impact requirements where applicable, and traceable inspection records. This approach keeps the grade comparison tied to real drill pipe performance rather than only to yield-strength numbers.
| API 5DP Grade | Minimum Yield Strength | Maximum Yield Strength | Minimum Tensile Strength |
|---|---|---|---|
| E75 | 75 ksi / 517 MPa | 105 ksi / 724 MPa | 100 ksi / 689 MPa |
| X95 | 95 ksi / 655 MPa | 125 ksi / 862 MPa | 105 ksi / 724 MPa |
| G105 | 105 ksi / 724 MPa | 135 ksi / 931 MPa | 115 ksi / 793 MPa |
| S135 | 135 ksi / 931 MPa | 165 ksi / 1138 MPa | 145 ksi / 1000 MPa |
From E75 to S135, the yield-strength window increases, but the grade should still be reviewed against the complete drill pipe assembly. For G105 and S135, higher pipe body strength can shift the limiting point toward the upset transition, thread area, tool joint shoulder or connection-side fatigue.
E75 vs X95 vs G105 vs S135 Drill Pipe Grade Selection Comparison
| API 5DP Grade | Typical Review Condition | Main Control Point | Next Review Step |
|---|---|---|---|
| E75 Drill Pipe | Conventional vertical wells, moderate tensile load and normal rotary torque | Hook load, OD / wall thickness, connection match and basic inspection records | Review X95 when tensile margin becomes limited or directional load increases |
| X95 Drill Pipe | Medium-depth wells, controlled directional sections and moderate torque increase | Tensile margin, torque demand, bending load and connection compatibility | Review G105 when X95 no longer provides enough load margin |
| G105 Drill Pipe | Deeper wells, directional drilling, controlled horizontal sections and higher combined load | Torque-drag, dogleg severity, cyclic bending, tool joint strength and connection review | Review S135 when hook load, long horizontal rotation or bending fatigue approaches the G105 margin |
| S135 Drill Pipe | Deep wells, high hook load, long horizontal sections, ERD or high-torque drilling | Fatigue exposure, connection torque, shoulder contact, tool joint matching and hardness / toughness review | Review a special material route when sour service, low-temperature toughness or severe fatigue controls the design |
E75, X95, G105 and S135 each have a suitable review range, and the final grade should match the well profile, fatigue exposure, connection capacity and inspection evidence.
E75 Drill Pipe: Baseline Grade for Moderate Drilling Load
E75 Drill Pipe provides the baseline API 5DP strength level, with 75 ksi / 517 MPa minimum yield strength, 105 ksi / 724 MPa maximum yield strength and 100 ksi / 689 MPa minimum tensile strength. It is reviewed for drilling programs where tensile load, torque, bending cycle and connection demand remain within a moderate range. Its role is not to compete with G105 or S135 in high-load sections, but to provide a stable grade basis where the well profile, OD / wall thickness, upset type and connection have enough design margin.
E75 is more suitable when:
- the well is vertical or only moderately directional
- hook load and torque remain within a controlled range
- dogleg severity is not a major fatigue driver
- no severe sour-service or low-temperature toughness requirement controls the design
- the selected size, wall thickness and connection provide enough design margin
E75 becomes less suitable when the well moves toward higher tensile load, longer directional sections, higher torque or repeated bending conditions. In that case, the grade review usually moves toward X95, G105 or S135.
X95 Drill Pipe: Intermediate Strength Between E75 and G105
X95 Drill Pipe provides an intermediate API 5DP strength level, with 95 ksi / 655 MPa minimum yield strength, 125 ksi / 862 MPa maximum yield strength and 105 ksi / 724 MPa minimum tensile strength. It is selected when E75 does not provide enough tensile-load margin, but the well profile still does not require G105 or S135. The review should focus on medium-depth drilling, controlled directional sections, increased torque demand and limited fatigue exposure.
X95 is commonly reviewed for:
- medium-depth wells with higher tension than E75 can comfortably support
- controlled directional wells
- drilling sections with increased torque but limited severe fatigue exposure
- applications where G105 or S135 may be more strength than the load case requires
- drill strings where connection compatibility and inspection records still support standard API grade review
The difference between X95 and G105 is not only a 10 ksi minimum yield-strength increase. The review should also consider whether the extra strength is needed for the actual load path. If the limiting factor is connection torque, dogleg fatigue or tool joint condition, moving to a higher pipe body grade alone may not solve the problem.
G105 Drill Pipe: Higher Strength for Deeper or Directional Wells
G105 Drill Pipe provides 105 ksi / 724 MPa minimum yield strength, 135 ksi / 931 MPa maximum yield strength and 115 ksi / 793 MPa minimum tensile strength. It offers a higher strength window than X95, but remains below S135, making it suitable for medium-to-deep directional wells, controlled horizontal sections and drilling intervals where torque, tension and cyclic bending increase but a high-strength S135 route is not yet required.
G105 grade review should include:
- tensile-load margin under planned well depth
- torque and drag along the directional section
- tool joint size, connection type and shoulder contact
- pipe marking, MTC and heat number traceability
A G105 Drill Pipe selection is usually reasonable when the main requirement is higher pipe body strength, while fatigue, connection and service-environment risks remain controlled. If the well profile includes long lateral rotation, high torque, severe dogleg or sour-service exposure, G105 still needs a deeper performance review instead of being selected by grade name alone.
S135 Drill Pipe: High-Strength API Grade for Higher Load Conditions
S135 Drill Pipe provides the common high-strength API baseline in this grade group. With a 135 ksi minimum yield-strength level, it is normally reviewed for deep wells, high hook load, long horizontal sections and drilling programs where the drill string needs a larger tensile-strength margin.
S135 is important because it expands the available strength window beyond E75, X95 and G105. But it should not be treated as the automatic best answer. Higher strength also makes toughness, hardness, fatigue-sensitive geometry and connection-side performance more important.
S135 should be reviewed carefully when:
- hook load approaches the practical margin of G105
- long horizontal or ERD sections increase torque and drag
- high dogleg severity creates repeated bending stress
- high make-up torque requires stronger connection review
- tool joint matching becomes critical to drill string performance
- hardness, toughness or cracking risk may control the service condition
For sour-service or H2S-containing environments, S135 should not be selected only because it has high strength. Sour-service use requires separate qualification logic, hardness control, cracking-risk review and project-specific acceptance requirements. A high-strength grade without the right service basis can create risk rather than solve it.
G105 vs S135 Drill Pipe: Strength Difference and Selection Logic
G105 vs S135 Drill Pipe is one of the most important comparisons in API 5DP grade selection. S135 has a higher minimum yield strength than G105, but this does not mean S135 is always the better choice.
The correct grade is determined by the limiting load path. G105 is usually enough when hook load, torque-drag, dogleg severity and connection capacity remain within the reviewed margin. S135 becomes more relevant when long horizontal rotation, high hook load or severe bending increases fatigue exposure near the upset transition, tool joint or thread shoulder. If the limiting point is connection torque, shoulder contact, impact toughness or service condition, increasing pipe body yield strength alone does not improve the actual drill string selection.
| Review Item | G105 Selection Basis | S135 Selection Basis |
|---|---|---|
| Tensile load | G105 provides enough design margin for the planned hook load and drill string weight. | Hook load approaches or exceeds the practical margin of G105. |
| Well profile | Directional sections are controlled, and dogleg severity remains moderate. | Long horizontal, ERD or severe dogleg sections increase bending and fatigue exposure. |
| Torque demand | Connection and tool joint capacity remain within the reviewed torque range. | High torque, shoulder loading or repeated make-up makes connection review critical. |
| Fatigue risk | Rotation and bending cycles remain within normal grade review. | Repeated bending near the upset transition or tool joint area becomes a key control point. |
| Service condition | No severe sour-service, low-temperature or special toughness requirement controls the grade. | Hardness, toughness, cracking resistance or service qualification requires stricter review. |
| Inspection evidence | Standard API grade records support the selected size, grade and connection. | Additional review of toughness, hardness, tool joint matching and traceability records is required. |
G105 is often a higher-strength working grade for deeper or directional drilling, while S135 is reviewed when the load case needs a high-strength API grade. Neither grade should be selected without checking the connection, fatigue exposure and inspection evidence.
Grade Selection by Drilling Condition
Before selecting E75, X95, G105 or S135, the review should separate load demand from failure risk. Vertical wells are mainly controlled by tensile load and normal torque, while long horizontal or ERD wells are controlled by torque-drag, cyclic bending and connection-side fatigue. Sour-service or low-temperature drilling requires hardness, impact toughness and cracking-resistance review beyond yield strength.
| Drilling Condition | Common Grade Review | Key Control Point |
|---|---|---|
| Conventional vertical well | E75 / X95 | Tensile load, normal torque, basic inspection records |
| Medium-depth directional well | X95 / G105 | Torque, bending load, connection compatibility |
| Deep well | G105 / S135 | Hook load, tensile margin, tool joint strength |
| Long horizontal well | G105 / S135 | Torque-drag, fatigue, dogleg severity |
| ERD well | S135 or special route review | Combined tension, torque, drag and fatigue |
| High-torque drilling | G105 / S135 | Make-up torque, shoulder contact, thread condition |
| Sour-service or H2S exposure | Sour-service route review | Hardness, SSC risk and service qualification basis |
| Low-temperature drilling | Grade plus toughness review | Charpy test temperature and absorbed energy requirement |
G105 is generally reviewed for deep or directional sections with controlled hook load, rotary torque and dogleg-related bending. S135 is more suitable when long lateral rotation, ERD torque-drag, high hook load or repeated bending near the upset transition and tool joint creates higher fatigue exposure and connection-side demand.The grade ranges in this table should be treated as engineering review boundaries rather than fixed selection rules. G105 Drill Pipe can be enough for a deep or directional well when tensile margin, dogleg severity and connection capacity remain controlled. S135 Drill Pipe becomes more relevant when high hook load, long horizontal rotation, ERD torque-drag or severe bending makes G105 margin insufficient.
Grade Selection Must Match Size, Upset Type and Connection
API 5DP grade selection should be checked together with the physical drill pipe design, not only the steel strength level. Even when the pipe body meets G105 or S135 strength, the final drill string performance can still be limited by wall thickness, internal clearance after upset, tool joint bore, connection torque capacity, shoulder contact or fatigue concentration near the upset transition.
| Review Area | Why It Matters |
|---|---|
| OD / wall thickness / nominal weight | Affects tensile capacity, internal clearance, handling weight and drill string design. |
| IU / EU / IEU upset type | Changes the transition geometry and internal or external clearance near the pipe end. |
| Tool joint OD / ID | Controls connection strength, bore clearance and torque-transfer capability. |
| Connection and shoulder contact | Determines make-up torque, thread engagement and load transfer. |
| Weld zone and transition area | Needs review because fatigue often concentrates near geometry changes. |
For G105 Drill Pipe and S135 Drill Pipe, the review should identify the first mechanical limit in the complete drill pipe assembly. Increasing the pipe-body grade improves tensile margin, but the operating load still passes through the upset transition, weld zone, tool joint bore, thread profile and shoulder face. If wall thickness, internal clearance, shoulder contact or tool joint dimensions are not matched to the same load case, the selected grade only strengthens the pipe body while the connection area remains the controlling risk point.
Inspection Records for API 5DP Drill Pipe Grade Acceptance
API 5DP drill pipe grade acceptance should be verified through a traceable record chain, not only by the grade marking on the pipe. The selected grade must be linked to the pipe identity, heat number, MTC, mechanical test results, dimensional inspection and tool joint / thread inspection. This ensures that E75, X95, G105 or S135 is supported by measurable test evidence and that the pipe body, connection and release documents refer to the same delivered drill pipe.
| Record Item | Why It Matters |
|---|---|
| Pipe marking | Confirms grade, size, connection and product identity. |
| Heat number | Links the pipe body and test data to the production heat. |
| MTC | Shows chemical composition and mechanical property basis. |
| Tensile test | Verifies yield strength, tensile strength and elongation. |
| Charpy impact test | Supports toughness review where required by grade, PSL or project specification. |
| Hardness record | Important for high-strength grade review, sour-service control or cracking-risk evaluation. |
| NDT report | Supports pipe body, weld zone and defect control. |
| Dimensional inspection | Confirms OD, wall thickness, length, straightness and upset area. |
| Tool joint inspection | Confirms tool joint dimensions, thread condition and shoulder quality. |
| Final release record | Connects the inspected product with the required grade and specification basis. |
A clear record chain should connect each inspection item in order:
Pipe marking → Heat number → MTC → Mechanical test report → Charpy impact test where required → Hardness record where required → NDT report → Dimensional inspection report → Tool joint and thread inspection → Final release record.
When API 5DP Grades Are Not Enough
Most drilling programs can be reviewed within the API 5DP Drill Pipe Grades system when the selected grade, size, connection and inspection records support the calculated load path. The limitation appears when the controlling factor is no longer basic yield strength, but cracking risk, low-temperature toughness, fatigue accumulation or connection-side performance.
A standard API grade becomes insufficient when the controlling factor is:
- severe sour-service or H2S exposure
- low-temperature impact toughness
- very long horizontal rotation
- severe dogleg fatigue
- high torque beyond normal connection review
- special connection or tool joint matching
- tighter hardness or microstructure control
- controlled yield-strength window requirement
When the limiting factor moves beyond standard grade strength, the review shifts from API 5DP Drill Pipe Grades to a Special Material Drill Pipe route, where chemistry, heat treatment, hardness, impact toughness, fatigue-sensitive geometry, tool joint matching and traceability records become the main control points.
FAQ
F1:What is the difference between E75, X95, G105 and S135 drill pipe?
Q1:The main difference is the API 5DP strength level. E75 Drill Pipe starts at 75 ksi minimum yield strength, X95 at 95 ksi, G105 at 105 ksi and S135 at 135 ksi. The grade should not be selected by yield strength alone. Well depth, hook load, torque, dogleg severity, fatigue exposure, upset type, tool joint condition and inspection records should be reviewed together.
F2:Is S135 Drill Pipe always better than G105 Drill Pipe?
Q2:No. S135 Drill Pipe has a higher strength level than G105 Drill Pipe, but it is not automatically the better grade. If G105 provides enough tensile margin and the connection, dogleg severity, torque and fatigue exposure remain controlled, G105 can be the more suitable API 5DP grade. S135 becomes more relevant when high hook load, long horizontal rotation or severe bending makes the G105 margin insufficient.
F3:How should API 5DP drill pipe grade be selected for deep or horizontal wells?
Q3:For deep or horizontal wells, API 5DP drill pipe grade selection should start with hook load and tensile margin, then move to torque-drag, dogleg severity, cyclic bending and connection capacity. G105 Drill Pipe is often reviewed for deeper or directional sections with controlled fatigue exposure. S135 Drill Pipe is reviewed when higher hook load, long lateral rotation or high torque makes the drill string load path more demanding.
F4:What records verify API 5DP Drill Pipe Grades?
Q4:API 5DP grade verification should be supported by a traceable record chain, not only by pipe marking. The key records include heat number, MTC, tensile test, Charpy impact test where required, hardness record where required, NDT report, dimensional inspection, tool joint inspection and thread inspection. These records confirm whether E75, X95, G105 or S135 is supported by actual test evidence for the delivered drill pipe.
