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API 5DP Drill Pipe Test Items: Tensile, Impact, Hardness, and Nondestructive Testing
Author:
WHH
Source:
LONGWAY
Published:
2026-10-14
Before leaving the factory, drill pipes undergo a series of tests to verify that their mechanical properties, chemical composition, and internal quality meet the required standards. The results of these tests are compiled into an MTC (Mill Test Certificate), which serves as the primary basis for procurement and acceptance. However, many purchasing professionals focus solely on whether the figures in the MTC are within specification, without fully understanding how those values were obtained, how the tests were conducted, or which stages are most prone to issues.
I. Why are factory acceptance tests necessary?
Drill pipe Underground, drill pipes are subjected to tensile, torsional, bending, and fatigue loads; failure may occur if any of these performance criteria are not met. The purpose of factory acceptance testing is to verify, using standardized procedures, that each batch of drill pipe complies with the design requirements of API 5DP.
The test items specified in API 5DP can be classified into three categories:
Material Property Testing: Verification of Chemical Composition and Mechanical Properties
Nondestructive Testing: Verifying Internal and Surface Quality
Process Validation Test: Verifies the quality of welding and heat treatment.
II. Tensile Test
Tensile testing is the most critical test for verifying the strength and ductility of drill pipes.
Test objective: To determine the yield strength, tensile strength, and elongation.
Sampling location: Samples are typically taken from the pipe body or the weld zone. For welded drill pipes, additional samples must also be taken from the weld seam for verification.
Test method:
Machine the specimen into a standard tensile test specimen.
Apply an axial tensile force on the universal testing machine.
Record the stress–strain curve and calculate the yield strength, tensile strength, and elongation.
API 5DP requirements:
| Steel grade | Minimum Yield Strength (psi) | Minimum tensile strength (psi) |
| E75 | 75,000 | 100,000 |
| X95 | 95,000 | 105,000 |
| G105 | 105,000 | 115,000 |
| S135 | 135,000 | 145,000 |
Elongation: API 5DP specifies a minimum elongation requirement, typically not less than 14% (depending on specimen size and gauge length).
Acceptance criteria: The yield strength and tensile strength specified on the MTC must simultaneously meet both the lower and upper limit requirements (with upper limits applicable to certain steel grades), and the elongation shall not be less than the specified minimum value.
III. Impact Test
Impact testing is used to evaluate the toughness of drill pipe materials under low-temperature or dynamic loading conditions, thereby preventing brittle fracture.
Test objective: To determine the Charpy V-notch impact energy (CVN).
Sampling locations: Samples are typically taken from the pipe body, the weld zone, and the heat-affected zone.
Test method:
Machined standard Charpy V-notch specimens
On the impact testing machine, cool the specimen to the specified temperature.
Impact the specimen with a pendulum and record the absorbed energy (in joules or foot-pounds).
API 5DP requirements:
At room temperature (21°C), the average of three impact test specimens shall be ≥16.3 J, with a minimum value of ≥13.6 J.
In low-temperature environments (e.g., −20°C or −40°C), the requirements may be more stringent; specific details shall be in accordance with the contract.
Critical Control Point: The impact test is highly sensitive to temperature. The specimen cooling temperature, holding time, and the interval between removal from the cooling medium and the impact test all influence the results. When placing an order, verify that the test temperature specified on the Material Test Certificate (MTC) complies with the project requirements.
IV. Hardness Test
Hardness testing is a rapid method for verifying the effectiveness of heat treatment and material homogeneity.
Test objective: To determine the Brinell hardness (HB) or the Rockwell hardness (HRC).
Test location:
Tube body
Tool connector
Weld zone
Heat-affected zone
API 5DP requirements:
Tool joint Brinell hardness: 285–341 HB
Weld surface hardness: For E/X/G/S steel grades, ≤ HRC 37; for SS steel grades, ≤ HRC 32.
Tube hardness: Meets the requirements of Table C.18 or D.18.
New requirements for Supplement No. 1 in 2025:
The hardness of the weld in SS sulfur-resistant steel grade shall be ≤ HRC 32.
The hardness test for the tube body is a newly added clause.
Acceptance criteria: Excessive hardness may indicate that the material is either too brittle or too soft. Over‑hardened welds are a common issue; during procurement, the hardness values on the Material Test Certificate (MTC) should be carefully verified.
V. Nondestructive Testing (NDT)
Nondestructive testing is a critical method for verifying the internal and surface quality of drill pipes.
| Detection method | Test subject | Applicable部位 |
| Ultrasonic Testing (UT) | Internal defects (cracks, inclusions) | Thickened transition zone, weld seam, pipe body |
| Magnetic Particle Testing (MT) | Surface and near-surface cracks | Thread, shoulder surface, and clamp‑on area |
| Magnetic Flux Leakage (MFL) Inspection | Tube body corrosion, wall thickness reduction | Overall length of the tube |
API 5DP requirements:
All drill pipes shall undergo full-length inspection to detect longitudinal defects.
The end of the drill pipe shall be inspected for transverse defects.
The weld zone shall undergo 100% UT and MT inspection.
For each batch (not exceeding 400 rods), one rod shall be selected for mechanical property testing.
Acceptance criteria: The MTC shall document the nondestructive testing methods, standards, and results. If the supplier cannot provide a nondestructive testing report, or if the report is overly brief (e.g., merely stating “Pass”), a request for a detailed supplementary report shall be made.
VI. Hydrostatic Test
Hydrostatic testing is used to verify the sealing integrity and strength of drill pipes under high pressure.
Test objective: To determine whether the pipe body or fittings exhibit leakage or deformation under high pressure.
Test method:
Seal both ends of the drill pipe.
Inject water or hydraulic fluid into the pipe and pressurize it to the specified pressure.
Maintain the pressure for a specified duration and observe whether any leakage or pressure drop occurs.
API 5DP requirements: Hydrostatic pressure testing is not a mandatory requirement for all drill pipes; it is typically performed as agreed upon in the purchase order. For high-pressure wells or critical projects, it is recommended to specify hydrostatic pressure testing.
Acceptance criteria: The test pressure, holding time, and leakage condition shall be recorded in the MTC.
VII. Common Issues in Procurement and Acceptance
| Question | Possible causes | Handling Recommendations |
| Tensile strength does not meet the standard. | Material composition deviations and improper heat treatment | Require the supplier to provide a retest report or reject the shipment. |
| Impact energy is relatively low. | Improper tempering temperature and coarse grain structure | Inspect heat treatment records and, if necessary, arrange for third-party re-inspection. |
| Hardness exceeds the standard. | Over-quenching or insufficient tempering | Require the supplier to adjust the process and deliver conforming products. |
| Nondestructive testing report missing | The supplier has not performed or provided it. | Supplementary testing is required, or third-party testing may be commissioned. |
| The furnace number does not match the MTC. | Management chaos or falsification | Reject this batch of products and re-evaluate the supplier. |
VIII. Frequently Asked Questions (FAQ)
Q1: Is the data on the MTC collected for every drill pipe?
No. Destructive tests such as tensile and impact tests are conducted on a lot-by-lot basis, while nondestructive testing is performed on each individual pipe in accordance with the applicable standards. Specific sampling frequencies are specified in API 5DP.
Q2: What role do third-party inspection agencies play in testing?
A third-party organization (SGS/BV/TÜV) may be stationed at the factory to witness the testing process or conduct retesting in a laboratory, and issue an EN 10204 Type 3.2 certificate.
Q3: How is the impact test temperature determined?
Determine based on the ambient operating temperature. For normal‑temperature wells, use 21°C; for low‑temperature environments, follow the project‑specific requirements (e.g., −20°C, −40°C).
Q4: Is a hydrostatic pressure test mandatory?
It is not mandatory, but it is recommended for high-pressure wells. Specific requirements shall be in accordance with the contract.
Q5: How can you determine whether a test report is reliable?
Verify whether the test methods comply with API 5DP, whether the sample‑taking locations are appropriate, whether the data are complete, and whether authorized signatures and the laboratory accreditation mark are present.
IX. Summary
| Test item | Objective | Key Requirements |
| Tensile test | Verification of Strength and Plasticity | Yield strength, tensile strength, and elongation meet the specified requirements. |
| Impact test | Validate resilience | CVN average and minimum values meet the standards. |
| Hardness test | Verify the heat treatment effect | Joint 285–341 HB, weld ≤ HRC 37/32 |
| Nondestructive testing | Verify internal and surface quality | UT+MT, 100% inspection |
| Hydrostatic test | Verify sealing and strength | Perform in accordance with the contract terms. |
Drill pipe factory acceptance testing represents the final safeguard of quality assurance. A clear understanding of the purpose and requirements of each test enables procurement personnel to focus on critical aspects during inspection, thereby avoiding being misled by a seemingly compliant MTC.
Need to learn more about drill pipe testing standards or procure API‑certified drill pipe for your project?
Contact Hebei Longway Petroleum Equipment Co., Ltd.
We supply a full range of API 5DP drill pipes, provide complete MTC reports, and support third-party inspections.
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