All About Oil Gas Water Heat Spiral Steel Pipe: Specifications, Performance, and Common Uses

Types of Oil, Gas, Water & Heat Spiral Steel Pipes

Spiral steel pipes are essential components in industrial and infrastructure applications, widely used for transporting oil, natural gas, water, and thermal energy. These pipes are manufactured using advanced forming techniques that provide high strength, durability, and resistance to extreme pressures and temperatures. Their spiral-welded construction offers superior structural integrity compared to traditional straight-seam pipes, making them ideal for demanding environments such as offshore platforms, underground pipelines, and district heating systems.

Seamless Spiral Steel Pipe

Despite the name, "seamless spiral" is a misnomer—true seamless pipes are not spiral-welded. However, this likely refers to spiral-welded steel pipes made from hot-rolled steel coils that are formed into a helical shape and then welded along the spiral seam. These pipes offer excellent strength-to-weight ratios and are capable of withstanding high internal pressure.

Advantages

• High structural strength due to spiral reinforcement
• Excellent pressure resistance for oil and gas transmission
• Long continuous lengths reduce the number of joints
• Cost-effective for large-diameter pipeline projects

Limitations

• Weld seam requires strict quality control
• Not suitable for ultra-high-pressure critical applications (where seamless tubes are preferred)
• Requires anti-corrosion coating for underground use

Best for: Long-distance oil & gas pipelines, water mains, and industrial fluid transport

Welded Spiral Steel Pipe

Manufactured using the Submerged Arc Welding (SAW) process, these pipes are constructed from steel plates rolled into a spiral form and welded along the helical seam. They often feature internal and external protective coatings such as fusion-bonded epoxy (FBE), polyethylene, or 3LPE (three-layer polyethylene) to resist corrosion, making them ideal for harsh environments including marine, underground, and high-temperature conditions.

Advantages

• Durable corrosion protection with dual-layer coatings
• Resistant to thermal expansion and contraction
• Excellent performance in fluctuating temperature environments
• Widely used in district heating and geothermal systems

Limitations

• Higher initial cost due to coating processes
• Requires careful handling to avoid coating damage
• Maintenance needed if coating is compromised

Best for: Underground pipelines, offshore applications, and heat distribution networks

Square Spiral Steel Pipe

While traditional spiral pipes are round, square spiral steel pipes represent a specialized structural variant. These are typically not spiral-welded in the conventional sense but may refer to square-section steel tubing used in structural frameworks with spiral reinforcement or helical bracing. Their geometry provides enhanced load-bearing capacity and ease of integration with other structural components.

Advantages

• Superior structural rigidity and stability
• Easier to connect and weld to flat surfaces and beams
• Ideal for modular construction and support frameworks
• Efficient space utilization in tight installations

Limitations

• Not typically used for high-pressure fluid transport
• Higher flow resistance compared to round pipes
• Limited availability in standard sizes

Best for: Structural supports, scaffolding, building frameworks, and mechanical systems

Colored Spiral Steel Pipe

These pipes are standard spiral-welded steel tubes with a colored polymer coating applied for identification, aesthetics, or environmental protection. The color coding helps differentiate between various fluid types (e.g., blue for water, red for fire lines, yellow for gas) in complex industrial setups. The coating also adds an extra layer of corrosion resistance and UV protection.

Advantages

• Visual identification improves safety and maintenance efficiency
• Protective coating extends service life
• Enhanced appearance for exposed installations
• Customizable colors for specific project needs

Limitations

• Color may fade under prolonged UV exposure
• Coating can be damaged during installation
• Slightly higher cost than uncoated variants

Best for: Industrial plants, HVAC systems, visible piping networks, and safety-critical applications

Expert Tip: For oil and gas applications, always ensure spiral-welded pipes meet international standards such as API 5L or ISO 3183. Regular inspection of weld seams and protective coatings is crucial to prevent leaks and ensure long-term reliability in high-pressure systems.

Industrial Applications of Oil, Gas, Water, and Heat Spiral Steel Pipe

Spiral steel pipes are a cornerstone of modern industrial infrastructure due to their exceptional strength, cost-efficiency, and adaptability. Manufactured by helically welding steel plates, these pipes offer a reliable solution for transporting fluids, gases, and solids under high pressure and temperature conditions. Their unique spiral construction provides structural resilience and flexibility, making them ideal for a wide range of demanding applications across multiple sectors.

Oil and Gas Pipelines

Spiral welded steel pipes are extensively used in the oil and gas industry for onshore and offshore pipeline networks. Their high tensile strength and ability to withstand internal pressures make them suitable for transporting crude oil, natural gas, and refined petroleum products over long distances.

The helical weld seam enhances the pipe’s flexibility, allowing it to endure ground movement and seismic activity without failure. Compared to seamless pipes, spiral steel pipes offer a more economical solution for large-diameter lines—often exceeding 24 inches—without sacrificing structural integrity. Additionally, they can be coated with anti-corrosion materials such as fusion-bonded epoxy (FBE) or polyethylene to ensure longevity in harsh environments.

Water Supply and Distribution Pipelines

In municipal and industrial water systems, spiral steel pipes are the preferred choice for large-scale water transmission mains. Their manufacturing process allows for diameters ranging from 20 inches to over 100 inches, enabling the efficient conveyance of vast volumes of potable water, wastewater, and raw water from reservoirs to treatment plants or distribution centers.

These pipes exhibit strong resistance to corrosion, especially when lined with cement mortar or protected with external coatings like coal tar enamel or 3LPE (three-layer polyethylene). This durability ensures minimal maintenance and extended service life, even when buried underground or submerged in aquatic environments.

Structural Applications in Construction

Beyond fluid transport, spiral steel pipes serve as critical structural components in commercial, industrial, and civil engineering projects. Their inherent strength-to-weight ratio and circular geometry make them ideal for use as foundation piles, bridge supports, transmission towers, and load-bearing columns in high-rise buildings.

The spiral welding technique enhances the pipe’s ability to distribute axial and lateral loads evenly, improving stability under dynamic stress conditions. These pipes can be easily customized in length and diameter, and they are compatible with various joining methods such as flanging, welding, or bolting, allowing seamless integration into complex architectural and engineering designs.

Thermal Power Plants – Steam and Water Circulation

In thermal power generation facilities, spiral steel pipes play a vital role in both primary and auxiliary systems. They are employed to transport high-pressure steam from boilers to turbines and to circulate feedwater throughout the plant.

Designed to endure continuous exposure to elevated temperatures (up to 450°C) and pressures exceeding 150 psi, these pipes maintain structural integrity in demanding thermal cycling environments. The smooth internal surface reduces flow resistance, enhancing energy efficiency and minimizing wear from turbulent fluid dynamics. Insulation and protective cladding are often added to reduce heat loss and prevent corrosion in humid or chemically aggressive zones.

Transportation of Bulk Solids in Mining and Industry

Spiral steel pipes are also utilized in pneumatic and gravity-based conveying systems for transporting abrasive solid materials such as coal, limestone, iron ore, and aggregates. Their robust construction resists wear and impact damage caused by continuous material flow.

The seamless interior finish—achieved through precision welding and internal grinding—minimizes friction and prevents material buildup, reducing the risk of clogging and ensuring consistent throughput. In mining operations, these pipes are commonly used in slurry transport lines, where they must endure both mechanical abrasion and chemical corrosion from mineral-laden water.

Benefits Summary

Important: Proper installation, including alignment, backfilling, and cathodic protection for buried pipelines, is essential to maximize performance and lifespan. Always adhere to international standards such as API 5L, ISO 3183, or ASTM A139 when specifying and installing spiral steel pipes. Using substandard materials or improper welding techniques can lead to catastrophic failures, environmental hazards, and costly downtime.

Product Specifications and Features of Oil, Gas, Water & Heat Spiral Steel Pipe

Spiral welded steel pipes are widely used in energy, infrastructure, and industrial applications due to their durability, strength, and cost-effective manufacturing process. These pipes are engineered to handle high-pressure fluid and gas transmission, structural support, and environmental protection systems. Understanding their technical specifications, installation methods, applications, and maintenance is essential for optimal performance and longevity.

Diameter Range

Spiral steel pipes are available in a broad diameter range to accommodate various flow requirements and pipeline designs.

• Standard diameters range from 16 to 64 inches (406 to 1626 mm), suitable for most commercial and industrial applications.
• For large-scale projects such as municipal water supply or cross-country oil/gas pipelines, custom diameters exceeding 64 inches can be manufactured.
• Larger diameters allow higher flow capacity with reduced friction loss, making them ideal for long-distance transmission systems.

Note: Custom tooling and specialized welding setups may be required for non-standard sizes.

Length Options

The length of spiral steel pipes is designed to balance transportability and installation efficiency.

• Standard pipe lengths are typically 6 meters (19.7 feet), which simplifies handling and logistics.
• For projects requiring fewer joints and improved integrity, extended lengths of up to 12 meters (39.4 feet) are available.
• Longer sections reduce the number of welds, lowering potential leak points and improving structural continuity.

Pro tip: Longer pipes may require special transportation permits and rigging equipment.

Wall Thickness

Wall thickness is a critical factor in determining the pressure rating and mechanical strength of the pipe.

• Available wall thickness ranges from 0.5 inches (12.7 mm) to 1.5 inches (38.1 mm), depending on service conditions.
• Thicker walls are used in high-pressure environments such as deep-water pipelines, oil refineries, and steam heating systems.
• Thin-walled variants are suitable for low-pressure water distribution or structural applications where weight is a concern.

Engineering insight: Wall thickness must be selected based on internal pressure, external loads, and corrosion allowances per ASME B31.4/B31.8 standards.

Steel Grades and Material Standards

The choice of steel grade directly impacts the pipe’s strength, toughness, and resistance to environmental stress.

• S235 (St37): Used for low-pressure applications such as drainage, irrigation, and non-critical structural supports.
• S355 (St52): Offers higher yield strength, making it ideal for medium to high-pressure oil, gas, and water pipelines.
• LSAW-grade steels: Often used in conjunction with spiral welding for enhanced weld integrity and impact resistance in extreme climates.
• Additional options include API 5L grades (e.g., X42, X52, X65) for oil and gas transmission pipelines.

Compliance note: Ensure material certifications (e.g., EN 10204 3.1 or 3.2) are provided for quality assurance.

Installation Process: Step-by-Step Guide

Proper installation ensures the structural integrity and operational safety of spiral steel pipe systems. Follow these best practices:

1. Site Preparation: Clear the trench or support structure of debris, rocks, and sharp objects that could damage the pipe coating or body.
2. Pipe Laying: Position the pipes using cranes or excavators with soft slings to prevent dents or deformation.
3. Welding & Joining: Use automated or semi-automatic submerged arc welding (SAW) machines to create strong, leak-proof spiral and girth welds. All welds should be inspected via ultrasonic testing (UT) or radiography (RT).
4. Support & Alignment: Install concrete saddles or steel cradles at regular intervals to maintain alignment and prevent sagging.
5. Pressure Testing: Conduct hydrostatic testing at 1.25–1.5 times the operating pressure to verify integrity before backfilling.
6. Backfilling & Protection: Cover pipes with fine sand or screened soil, avoiding large rocks. Apply cathodic protection and corrosion-resistant coatings as needed.

Expert Advice: Always follow local codes and engineering specifications. Pre-fabricated spools can reduce field welding time and improve quality control.

Applications and Use Cases

Spiral steel pipes serve a wide range of industries due to their versatility and robust construction:

• Oil & Gas Transportation: Used in onshore and offshore pipelines for crude oil, natural gas, and refined products.
• Water Supply & Sewer Systems: Ideal for large-diameter municipal water mains, stormwater drainage, and wastewater conveyance.
• Industrial Process Piping: Transport slurries, chemicals, steam, and heated fluids in power plants, refineries, and mining operations.
• Structural Applications: Serve as foundation piles, bridge supports, and offshore platform legs due to high load-bearing capacity.
• Environmental Protection: Act as containment barriers, pollution control conduits, and erosion prevention systems.
• Electrical & Utility Conduits: Provide durable protective casings for high-voltage cables and fiber optics.

Innovation spotlight: Internally lined or coated pipes (e.g., epoxy, FBE, or cement mortar) enhance flow efficiency and corrosion resistance.

Maintenance and Repair Guidelines

Regular maintenance extends service life and prevents costly failures. Implement a proactive inspection and repair strategy:

• Visual Inspections: Check for surface cracks, corrosion, dents, coating damage, and support degradation every 6–12 months.
• Non-Destructive Testing (NDT): Use ultrasonic thickness gauging and magnetic particle inspection to detect internal flaws or wall thinning.
• Corrosion Control: Maintain cathodic protection systems and reapply protective coatings as needed, especially in humid or saline environments.
• Internal Cleaning: Perform pigging operations or chemical cleaning to remove scale, sediment, or biofilm buildup that reduces flow efficiency.
• Repair Methods:
  • Small leaks or cracks can be repaired using patch welding or sleeve repairs.
  • Severe damage may require pipe spool replacement or composite wrap reinforcement.
• Record Keeping: Maintain detailed logs of inspections, repairs, pressure tests, and coating conditions for compliance and predictive maintenance.

Preventative Strategy: Implement a Condition-Based Maintenance (CBM) program using sensors and monitoring systems to detect early signs of failure, reducing downtime and emergency repairs.

Final Recommendation: When selecting spiral steel pipes, always match the material, dimensions, and protective features to the specific operational environment. Partner with certified manufacturers who adhere to international standards (e.g., ISO 3183, API 5L, EN 10217) and provide full traceability. Investing in quality upfront significantly reduces lifecycle costs and enhances system reliability.

Spiral Steel Pipe Customization Options

Spiral steel pipes are highly versatile and widely used in industries such as oil and gas, construction, water supply, and infrastructure due to their strength, durability, and adaptability. These pipes can be extensively customized based on a variety of technical and operational requirements to ensure optimal performance in specific environments and applications. Whether you need pipes for high-pressure systems, corrosive environments, or specialized installations, manufacturers offer comprehensive customization options to meet your exact needs.

Important Note: Proper customization ensures compliance with safety standards, enhances system efficiency, and extends service life. Always consult engineering specifications and industry regulations when selecting custom features for your spiral steel pipe project.

Material Selection and Corrosion Protection

The choice of material is one of the most critical factors in determining the performance and longevity of spiral steel pipes. Depending on the application environment, customers can select from various steel types, each offering unique mechanical and chemical properties:

• Carbon Steel: Ideal for general-purpose applications due to its high strength, weldability, and cost-effectiveness. Common grades include API 5L Gr.B, X42, X52, X60, X65, and X70.
• Alloy Steel: Enhanced with elements like chromium, molybdenum, or nickel to improve toughness, wear resistance, and performance under extreme conditions.
• Stainless Steel: Offers superior corrosion resistance and is suitable for aggressive environments, including marine or chemical processing applications.

In addition to base materials, spiral pipes can be protected with advanced anti-corrosion coatings such as:

• Fusion-Bonded Epoxy (FBE)
• 3LPE (Three-Layer Polyethylene) and 3LPP (Three-Layer Polypropylene)
• Coal Tar Enamel
• External wrapping with polytape or bituminous coating
• Internal linings (e.g., epoxy, polyurethane) for fluid compatibility and reduced friction

Expert Tip: For underground or submerged installations, consider dual-layer protection (external coating + cathodic protection) to maximize resistance against soil and water corrosion.

Custom Dimensions and Tolerances

Beyond standard sizes, spiral steel pipes can be manufactured to precise dimensional specifications tailored to project requirements. This flexibility allows seamless integration into complex piping systems and infrastructure projects.

• Diameter Range: Typically from 219 mm (8") up to 3600 mm (142"), with custom diameters available upon request.
• Wall Thickness: Adjustable from 6 mm to over 30 mm depending on pressure rating and structural needs.
• Length: Standard lengths range from 6 to 12 meters, but longer or non-standard lengths can be produced for special applications (e.g., river crossings, offshore platforms).
• Tolerance Compliance: Manufactured to meet international standards such as API 5L, ASTM A139, GB/T 9711, and ISO 3183, ensuring dimensional accuracy and consistency.

End Finishing and Joining Options

The end configuration of spiral steel pipes plays a crucial role in connection integrity, installation speed, and system reliability. Various finishing options are available to suit different joining methods:

• Beveled Ends: Prepared for automatic or manual welding, commonly used in pipeline construction.
• Plain Ends: Suitable for coupling or flange connections.
• Threaded Ends: Available with API buttress or round threads for quick assembly without welding.
• U & V Grooves: Pre-cut groove profiles to facilitate field welding with proper penetration and strength.
• Flanged Ends: Equipped with ANSI, DIN, or JIS standard flanges for bolted connections in industrial systems.

Custom joint designs can also be developed for unique project demands, ensuring leak-proof and mechanically sound connections.

Certifications and Quality Assurance Testing

To ensure reliability and compliance with global standards, every batch of spiral steel pipes undergoes rigorous quality control and testing procedures. Customers can request certified products that meet specific regulatory and industry requirements.

Common Testing Procedures Include:

• Hydrostatic Testing: Verifies the pipe’s ability to withstand operating pressure without leakage.
• Ultrasonic Testing (UT) & X-Ray Inspection: Detects internal defects such as cracks, porosity, or incomplete weld fusion in the spiral seam.
• Chemical Composition Analysis: Confirms material grade conformity using spectrometry.
• Mechanical Testing: Includes tensile strength, impact toughness (Charpy V-notch), and hardness tests.
• Dimensional and Visual Inspection: Ensures compliance with specified tolerances and surface quality.

Available Certifications:

• API 5L (American Petroleum Institute)
• ISO 3183 (Petroleum and natural gas industries – Steel pipe for pipeline transportation systems)
• GB/T 9711 (Chinese national standard)
• EN 10217 (European standard for welded steel tubes)
• Mill Test Certificate (MTC) 3.1 or 3.2 as per EN 10204

Specialized Features for Enhanced Performance

For demanding applications, spiral steel pipes can be enhanced with specialized features to improve functionality and environmental resistance:

• High-Pressure & High-Temperature (HPHT) Resistance: Designed for oil and gas extraction, geothermal systems, and industrial boilers.
• Porous or Perforated Pipes: Used in drainage, filtration, and geotechnical applications to allow controlled fluid passage.
• Internal Lining: Options include cement mortar, epoxy, polyurethane, or HDPE lining to prevent corrosion, reduce scaling, and improve flow efficiency.
• Insulation Coating: For thermal protection in steam or cryogenic transport lines.
• Anti-Buckling Design: Reinforced wall thickness or stiffening rings for deep-sea or underground installations.

Availability and Supply Options

Spiral steel pipes are produced in large-scale manufacturing facilities equipped with automated production lines, ensuring consistent quality and fast turnaround. They are readily available for:

• Bulk orders and wholesale supply
• Custom production runs with short lead times
• Just-in-time delivery for large infrastructure projects
• International shipping with proper packaging and documentation

Manufacturers maintain extensive inventory and offer flexible logistics support to accommodate urgent or high-volume demands across global markets.

Procurement Tip: When placing large or recurring orders, consider negotiating long-term supply agreements to secure pricing stability, priority production scheduling, and dedicated quality control oversight.

In summary, spiral steel pipes offer unmatched customization potential across material, dimensions, finishing, certification, and performance-enhancing features. By leveraging these options, engineers and project managers can design robust, efficient, and compliant piping systems tailored to the most challenging environments. Always work with reputable suppliers who provide full traceability, testing documentation, and technical support throughout the procurement and installation process.

Frequently Asked Questions About Oil, Gas, Water & Heat Spiral Steel Pipes

Understanding the technical and practical aspects of spiral steel pipes is essential for engineers, contractors, and procurement professionals involved in energy, infrastructure, and industrial projects. Below are detailed answers to common questions about spiral welded steel pipes used in oil, gas, water, and heating systems.

A1: While the terms are often used interchangeably, there are key technical distinctions between pipes and tubes:

• Shape & Design: Pipes are almost always round and manufactured to standardized dimensions (such as NPS – Nominal Pipe Size), while tubes can be round, square, rectangular, or custom-shaped.
• Sizing Standards: Pipes are sized by nominal bore (e.g., 6-inch pipe), which doesn’t exactly match the outer diameter, whereas tubes are typically specified by exact outside diameter (OD) and wall thickness (e.g., 2" OD x 0.120" wall).
• Application: Pipes are primarily used for transporting fluids and gases under pressure—common in oil & gas, water supply, and HVAC systems. Tubes are frequently used in structural applications (e.g., scaffolding, handrails) and precision machinery due to tighter dimensional tolerances.
• Material & Wall Thickness: Pipes generally have thicker walls and are designed for high-pressure environments. Tubes may have thinner walls and are often made from materials like stainless steel, aluminum, or copper for specialized uses.

In the context of spiral steel pipes, these are classified as pipes because they are round, pressure-rated, and used for large-scale fluid conveyance in pipeline networks.

A2: The distinction lies in scale, function, and system integration:

• Pipe: A single cylindrical section made of steel, plastic, or other materials. It is a component used in various systems and comes in standard or custom lengths (typically 6m, 12m, or random lengths).
• Pipeline: A complete engineered system composed of multiple connected pipes, along with valves, pumps, compressors, monitoring equipment, and protective coatings. Pipelines are designed to transport substances—such as crude oil, natural gas, water, or steam—over long distances, sometimes spanning hundreds or thousands of kilometers.
• Scope: A pipe is a building block; a pipeline is the entire infrastructure network. For example, a spiral welded steel pipe might be one segment in a transcontinental oil pipeline.
• Design Considerations: Pipelines require route planning, environmental assessments, corrosion protection, pressure testing, and regulatory compliance, far beyond the scope of individual pipe specifications.

Spiral welded pipes are commonly selected for pipeline construction due to their cost-effectiveness, strength, and ability to be produced in large diameters (up to 3000mm or more), making them ideal for major transmission lines.

A3: Spiral welded steel pipes (also known as SAWL – Submerged Arc Welded Longitudinal pipes) are widely used across multiple industries due to their durability, weld integrity, and adaptability to large diameters. Key applications include:

• Oil & Gas Transportation: Used in onshore and offshore pipelines for conveying crude oil, refined petroleum, and natural gas over long distances.
• Water Supply Systems: Employed in municipal water distribution, irrigation networks, and seawater intake lines due to their resistance to internal pressure and external loads.
• Industrial Fluid Transfer: Ideal for moving chemicals, slurry, and process water in power plants, refineries, and mining operations.
• District Heating Networks: Used in insulated underground heat distribution systems where thermal expansion and high operating temperatures demand robust piping.
• Structural Applications: Utilized as foundation piles, bridge supports, and offshore platform legs because of their high load-bearing capacity and circular strength.

The spiral manufacturing process allows for controlled welding angles and uniform stress distribution, enhancing the pipe’s ability to withstand fluctuating pressures and temperature variations—critical in dynamic environments like heating systems or deep-water pipelines.

A4: Spiral steel pipes are engineered for exceptional longevity, with service lives typically exceeding 50 years, and in well-maintained conditions, some can last over 80 years. Several factors contribute to this durability:

• High-Quality Steel: Made from carbon steel grades like API 5L (Gr. B, X42–X80), which offer excellent tensile strength and toughness.
• Corrosion Protection: Equipped with external coatings (e.g., FBE – Fusion Bonded Epoxy, 3LPE, or coal tar enamel) and internal linings to resist rust and chemical degradation.
• Cathodic Protection: Often paired with sacrificial anodes or impressed current systems to prevent electrochemical corrosion, especially in buried or submerged installations.
• Robust Welding: The spiral weld is continuously inspected using ultrasonic and radiographic testing to ensure integrity and leak resistance.
• Environmental Resilience: Designed to perform in harsh conditions—including extreme temperatures, high pressure, and corrosive soils or seawater.

Lifespan also depends on proper installation, maintenance, and operational conditions. Regular inspection and monitoring (e.g., smart pigging in pipelines) further extend service life and ensure safety and reliability.

A5: Yes, custom spiral steel pipes generally require a longer delivery time compared to standard stock items, but several factors influence the lead time:

• Manufacturing Process: Custom pipes are produced to specific requirements—diameter, wall thickness, length, steel grade, coating type, and testing standards—which requires dedicated production scheduling and quality checks.
• Typical Lead Times: Standard orders may ship in 4–8 weeks, while complex custom projects can take 10–16 weeks or more, depending on factory workload and material availability.
• Stock Availability: Occasionally, manufacturers may have pre-produced pipes that match customer specs already in inventory, allowing for faster delivery. However, this is rare for highly customized orders.
• Additional Services: Orders requiring third-party inspection (e.g., SGS, BV), special packaging, or international certifications (e.g., API, ISO, CE) add time to the process.
• Logistics: Transporting large-diameter or heavy pipes may involve special handling, route planning, and export documentation, further affecting delivery timelines.

To minimize delays, it’s advisable to finalize technical specifications early and coordinate closely with suppliers during project planning. Many manufacturers offer expedited production for urgent projects, though at an additional cost.