S135 Steel: Properties and Key Applications in Drill Pipe

S135 steel, classified as a medium-carbon alloy steel, is primarily used in the manufacturing of drill pipes for the oil and gas industry. This steel grade is characterized by its high strength and toughness, making it suitable for demanding applications in harsh environments. The primary alloying elements in S135 steel include carbon, manganese, and chromium, which contribute to its mechanical properties and overall performance.

Comprehensive Overview

S135 steel is specifically designed for use in drill pipes, where it must withstand high levels of stress and fatigue during drilling operations. The medium-carbon content provides a balance between strength and ductility, allowing the steel to endure the dynamic loads encountered in drilling applications. The addition of manganese enhances hardenability and improves wear resistance, while chromium contributes to corrosion resistance and overall toughness.

Advantages of S135 Steel:
- High Strength: S135 steel exhibits excellent tensile and yield strength, making it suitable for deep drilling applications.
- Good Toughness: The steel's toughness ensures that it can absorb energy and resist fracture under impact loads.
- Corrosion Resistance: The alloying elements provide a degree of resistance to corrosive environments, which is critical in oil and gas applications.

Limitations of S135 Steel:
- Cost: Compared to lower-grade steels, S135 can be more expensive due to its alloying elements and processing requirements.
- Weldability: While S135 can be welded, it requires careful consideration of pre- and post-weld heat treatments to avoid cracking.

Historically, S135 steel has played a significant role in the development of drilling technologies, providing the necessary strength and durability for modern drilling operations. Its market position is well-established, particularly in regions with extensive oil and gas exploration activities.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S13500	USA	Closest equivalent to API 5DP
API	135	USA	Standard for drill pipe
ASTM	A53	USA	Similar properties, but not specifically for drill pipe applications
EN	10225	Europe	Minor compositional differences
JIS	G3444	Japan	Similar applications in structural use

The table above highlights the various standards and equivalents for S135 steel. While some grades may appear similar, subtle differences in composition can affect performance, particularly in high-stress applications like drilling. For instance, while API 5DP is a standard for drill pipe, S13500 is specifically tailored for enhanced mechanical properties.

Key Properties

Chemical Composition

Element (Symbol)	Percentage Range (%)
Carbon (C)	0.28 - 0.34
Manganese (Mn)	0.60 - 0.90
Chromium (Cr)	0.20 - 0.40
Phosphorus (P)	≤ 0.025
Sulfur (S)	≤ 0.025

The primary alloying elements in S135 steel play crucial roles:
- Carbon: Increases hardness and strength but can reduce ductility if too high.
- Manganese: Enhances hardenability and wear resistance, critical for drill pipe applications.
- Chromium: Improves corrosion resistance and overall toughness, essential for durability in harsh environments.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric)	Typical Value/Range (Imperial)	Reference Standard for Test Method
Tensile Strength	Quenched & Tempered	620 - 700 MPa	90 - 102 ksi	ASTM E8
Yield Strength (0.2% offset)	Quenched & Tempered	450 - 550 MPa	65 - 80 ksi	ASTM E8
Elongation	Quenched & Tempered	15 - 20%	15 - 20%	ASTM E8
Hardness (Rockwell)	Quenched & Tempered	28 - 34 HRC	28 - 34 HRC	ASTM E18
Impact Strength	-	40 J at -20°C	29.5 ft-lbf at -4°F	ASTM E23

The mechanical properties of S135 steel make it particularly suitable for applications that require high strength and toughness. The combination of high tensile and yield strength allows it to withstand significant mechanical loading, while the elongation and impact strength ensure that it can absorb energy without fracturing.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	-	7.85 g/cm³	0.284 lb/in³
Melting Point	-	1425 - 1540 °C	2600 - 2800 °F
Thermal Conductivity	20°C	50 W/m·K	34.5 BTU·in/h·ft²·°F
Specific Heat Capacity	20°C	0.46 kJ/kg·K	0.11 BTU/lb·°F

Key physical properties such as density and thermal conductivity are significant for applications involving heat transfer and structural integrity. The density of S135 steel indicates its robustness, while its thermal conductivity suggests moderate heat transfer capabilities, which can be crucial in drilling operations where temperature management is essential.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-5	25°C/77°F	Fair	Risk of pitting corrosion
Sulfuric Acid	10	20°C/68°F	Poor	Not recommended
Atmospheric	-	Varies	Good	Moderate resistance

S135 steel exhibits fair resistance to chlorides, which is crucial in offshore drilling environments. However, its performance in acidic conditions is poor, necessitating careful consideration when used in such environments. Compared to other grades like API 5L X65, which offers better corrosion resistance, S135 may require additional protective measures in highly corrosive environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400°C	752°F	Suitable for moderate heat
Max Intermittent Service Temp	500°C	932°F	Short-term exposure only
Scaling Temperature	600°C	1112°F	Risk of oxidation at high temps

S135 steel maintains its mechanical properties up to moderate temperatures, making it suitable for applications where heat is a factor. However, at temperatures exceeding 400°C, the risk of oxidation and scaling increases, which can compromise the integrity of the material.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
SMAW	E7018	Argon + CO2	Preheat recommended
GMAW	ER70S-6	Argon	Post-weld heat treatment needed

S135 steel can be welded using various methods, but it requires careful attention to pre- and post-weld heat treatments to prevent cracking. The use of low-hydrogen filler metals is recommended to maintain the integrity of the weld.

Machinability

Machining Parameter	S135 Steel	AISI 1212	Notes/Tips
Relative Machinability Index	60%	100%	S135 is more challenging to machine
Typical Cutting Speed	30 m/min	50 m/min	Use carbide tools for best results

Machinability of S135 steel is moderate, requiring appropriate tooling and cutting speeds to achieve optimal results. The higher carbon content can lead to increased tool wear, necessitating the use of high-quality cutting tools.

Formability

S135 steel exhibits moderate formability, suitable for cold and hot forming processes. However, due to its medium-carbon content, it may experience work hardening during cold forming, which can limit the extent of deformation without cracking. Recommended bend radii should be adhered to, ensuring that the material does not exceed its limits during forming operations.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	600 - 700 °C / 1112 - 1292 °F	1 - 2 hours	Air	Improve ductility and reduce hardness
Quenching	800 - 900 °C / 1472 - 1652 °F	30 minutes	Oil	Increase hardness and strength
Tempering	400 - 600 °C / 752 - 1112 °F	1 hour	Air	Reduce brittleness and improve toughness

Heat treatment processes significantly influence the microstructure and properties of S135 steel. Quenching increases hardness, while tempering helps to relieve stresses and enhance toughness, making it suitable for high-stress applications.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Oil and Gas	Drill pipes	High tensile strength, toughness	Required for deep drilling
Mining	Casing pipes	Corrosion resistance, strength	Durability in harsh conditions
Construction	Structural components	High strength, weldability	Essential for structural integrity

S135 steel is predominantly used in the oil and gas industry for drill pipes, where its high strength and toughness are critical. Additionally, it finds applications in mining and construction, where durability and resistance to harsh environments are paramount.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	S135 Steel	API 5L X65	AISI 4140	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate strength	High strength	S135 offers better toughness
Key Corrosion Aspect	Fair resistance	Good resistance	Fair resistance	API 5L X65 is better for corrosive environments
Weldability	Moderate	Good	Good	S135 requires careful treatment
Machinability	Moderate	Good	Moderate	S135 is more challenging to machine
Approx. Relative Cost	Moderate	Moderate	Low	Cost varies by application
Typical Availability	Common	Common	Common	Widely available in industry

When selecting S135 steel for specific applications, considerations such as cost, availability, and mechanical properties are crucial. While S135 offers excellent strength and toughness, its weldability and machinability may present challenges. Comparatively, grades like API 5L X65 provide better corrosion resistance, making them suitable for different environments.

In conclusion, S135 steel is a vital material in the oil and gas industry, offering a unique combination of strength, toughness, and moderate corrosion resistance. Its properties make it suitable for demanding applications, but careful consideration of its limitations and fabrication properties is essential for optimal performance.