Van Leeuwen GmbH

1 Project Background and Engineering Requirements

The Julius Nyerere Hydropower Project (JNHPP) is one of Tanzania’s most critical infrastructure projects in recent years. Located on the Rufiji River, it has a total installed capacity of 2,115 megawatts and is expected to significantly enhance the country’s power supply capacity and promote socio-economic development upon completion. The project comprises several key components, including dams, powerhouses, water conveyance systems, and transmission facilities, all of which impose stringent requirements on the piping systems. The pipes must handle high-pressure water flow, withstand geological settlement and temperature variations, and guarantee a service life of over 50 years. Therefore, the selection of piping materials directly impacts the project’s safety, economy, and long-term reliability.

The JNHPP environment presents the following characteristics:

• High water pressure impact: Penstocks and turbine conduits in hydropower plants must withstand extremely high internal water pressure, requiring piping materials with high tensile strength and fatigue resistance.
• Complex geological conditions: The project site may experience foundation settlement or geological shifts, necessitating piping systems with certain flexibility and deformation resistance.
• Corrosive environment: Water and soil may be corrosive, requiring materials with excellent corrosion resistance to ensure long-term reliability.
• Installation efficiency requirements: The project’s large scale and tight schedule demand easy installation of piping systems that can adapt to modular construction and rapid assembly.

To address these needs, the JNHPP has selected high-quality piping materials and connectors such as welded/SMLS pipes (100MM-650MM), BW fittings, forged flanges, forged fittings, GARLOCK gaskets, and ductile iron fittings. These materials provide a comprehensive and reliable solution for the project through their exceptional mechanical properties, excellent corrosion resistance, and dependable sealing performance. The table below summarizes the alignment between the JNHPP’s core requirements and the performance of the selected piping materials and fittings:

Table: Alignment Between JNHPP Core Requirements and Piping Materials/Fittings Performance

2 Advantages of Welded and Seamless (SMLS) Pipes

In the Julius Nyerere Hydropower Project (JNHPP), welded steel pipes and seamless (SMLS) pipes within the 100MM-650MM diameter range each demonstrate unique advantages to meet the project’s varying operational conditions. Welded steel pipes, particularly those produced using submerged arc welding (SAW) and high-frequency induction (HFI) technologies, are ideal for large-diameter water conveyance pipelines and general pressure systems due to their superior cost-effectiveness and production efficiency. Their manufacturing process uses coiled steel plates as raw material, formed through continuous welding, which not only reduces raw material costs but also meets the project’s high demand for large-diameter pipelines. For example, LSAW (Longitudinal Submerged Arc Welding) pipes, rolled and welded from wide steel plates, offer high radial strength and stability, making them highly suitable for sections within JNHPP that withstand relatively high internal water pressure with moderate fluctuations, such as certain water diversion tunnels and drainage systems.

Seamless (SMLS) pipes, on the other hand, are formed by piercing technology that creates a hollow shell from a solid billet without any welding process. This results in excellent overall structural continuity without the potential weak point of a weld seam, thus providing higher uniformity and reliability. In critical high-pressure areas of the JNHPP, particularly penstocks before turbines, high-pressure bypass systems, and oil pipelines for governor systems, these sections endure severe water hammer effects and sustained high-pressure loads, demanding utmost safety. SMLS pipes, with their outstanding pressure resistance and fatigue resistance, are the necessary choice for these crucial areas. They effectively prevent potential cracking caused by pressure fluctuations, providing a solid foundation for the power station’s safe and stable operation.

Furthermore, modern manufacturing technologies ensure that both welded and seamless pipes meet strict dimensional tolerance requirements. Welded pipes typically feature tighter dimensional tolerances, while the wall thickness uniformity of seamless pipes continues to improve. This is crucial for the installation precision and system fluidity of the JNHPP, ensuring optimal alignment during welding or flange connections, reducing installation stress, and thereby enhancing the integrity and reliability of the entire piping system.

3 Advantages of Butt-Weld (BW) Fittings

In the Julius Nyerere Hydropower Project (JNHPP), butt-weld (BW) fittings (including elbows, tees, reducers, etc.) play a vital role in pipeline connections within the 100MM-650MM diameter range. Their advantages primarily lie in exceptional connection strength, excellent fluid performance, and high reliability.

Butt-weld fittings form a permanent metallurgical bond with the pipe through groove processing and welding techniques, with connection strength often matching or exceeding that of the pipe material itself. This robust connection makes BW fittings particularly suitable for critical pipeline sections in JNHPP that endure high pressure, high thermal stress, or substantial thrust from direction changes, such as bends in high-pressure water conveyance tunnels, turbine inlets, and pipeline connections before and after valve groups. Compared to mechanical connection methods (e.g., threaded or flanged connections), butt-welded joints eliminate potential leakage points and the risk of loosening due to vibration, providing extremely high system integrity.

• Smooth fluid transmission: The smooth internal surface formed by butt-welding (with ideal welding and subsequent treatment) minimizes fluid turbulence and pressure loss. This is crucial for large hydropower stations like JNHPP, where efficiency is paramount. Smooth fluid characteristics help ensure power generation efficiency and reduce energy loss during conveyance.
• Compact structure and space savings: Welded connections do not require the bolt operation space needed for flanged connections, resulting in a more compact system that not only saves space but may also reduce the need for additional support structures. This advantage is particularly evident in pipeline layouts within the powerhouse where space is relatively limited.
• Cost-effectiveness and long-term reliability: Although the initial installation cost of butt-welded connections (due to higher requirements for welder skills, non-destructive testing, etc.) may be higher than some mechanical connections, their maintenance-free nature and long service life offer better economy over the project’s entire lifecycle. Once high-quality welding is completed and inspected, its reliability is extremely high, requiring almost no post-installation maintenance.

During JNHPP’s construction, to fully leverage the advantages of butt-weld fittings, the project implemented strict welding procedure qualifications (WPS/PQR), used low-hydrogen electrodes (such as J427 welding rods), and performed precision non-destructive testing (e.g., RT radiography or UT ultrasonic testing). These measures collectively ensure that every butt-welded joint meets the project’s stringent quality and safety requirements.

4 Advantages of Forged Flanges and Fittings

In the Julius Nyerere Hydropower Project (JNHPP), forged flanges and forged fittings (100MM-650MM) are indispensable components of the piping system. They play a crucial role in high-pressure, critical applications thanks to their exceptional mechanical properties and unparalleled reliability.

The forging process involves applying enormous pressure to metal billets using forge hammers or presses, causing plastic deformation to achieve the desired shape and size. This process effectively refines metal grains and eliminates defects such as casting porosity, air pockets, and inclusions, resulting in a more dense and uniform internal structure and complete flow lines. Consequently, forged flanges and fittings offer higher strength, better toughness, and superior fatigue and impact resistance compared to cast products. This is vital for the JNHPP power station’s piping system, which must withstand severe water hammer effects, high-pressure fluctuations, and potential vibrations, especially at critical connection points such as main unit outlets, both sides of main valves, and high-pressure bypasses.

Another significant advantage of forged flanges is their excellent sealing reliability. They can form an excellent partnership with high-performance gaskets like GARLOCK. Through precisely machined sealing surfaces (e.g., raised face RF, tongue and groove T/G), they achieve ultimate sealing performance under bolt preload, effectively preventing high-pressure water leakage and ensuring the power station’s safe and stable operation.

Moreover, forged components typically have lower carbon content and a uniform structure, giving them better corrosion resistance than cast components. In JNHPP’s potentially moisture-corrosive environment, this translates to longer service life and lower maintenance costs.

Table: Performance Comparison Between Forged and Cast Flanges/Fittings

In the JNHPP project, for medium-low pressure auxiliary systems that do not endure extreme conditions but still require reliability (e.g., some drainage and cooling water systems), high-quality castings might be used to balance costs. However, for all core high-pressure, high-risk areas, forged flanges and forged fittings are undoubtedly the more reliable choice to ensure the power station’s safe and stable operation for decades, thanks to their indisputable performance advantages.

5 Advantages of GARLOCK Gaskets

In the complex piping system of the Julius Nyerere Hydropower Project (JNHPP), flange connections are ubiquitous, and gaskets, as critical sealing elements in these connections, directly determine whether the entire system can achieve leak-free safe operation. GARLOCK gaskets, as representatives of high-performance sealing solutions, demonstrate significant multifaceted advantages in this project.

The GARLOCK gasket product range can adapt to the various media, pressures, and temperatures present in the JNHPP project, directly influencing flange gasket selection. For instance, its non-metallic gaskets (e.g., made from specialty synthetic fibers, flexible graphite, or PTFE) are suitable for water, air, and various industrial fluids, offering good sealing and economy. For critical high-temperature and high-pressure conditions, GARLOCK’s semi-metallic gaskets (e.g., spiral wound gaskets) and metallic gaskets perform exceptionally. These gaskets are designed to withstand pressures up to 1200 psi (approximately 8.27 MPa) and extreme temperatures ranging from -450°F to 800°F (approximately -268°C to 427°C), fully covering the needs of various systems in the JNHPP power station. Suitable models can be found for everything from conventional water systems to high-temperature steam lines.

• Exceptional Sealing Performance: GARLOCK gaskets are designed to create tight static seals by filling the microscopic imperfections between two flange faces, effectively preventing liquid or gas leakage. Their precise manufacturing ensures gaskets have uniform density and accurate dimensions, achieving optimal sealing performance under specified bolt torque, significantly reducing the risk of downtime and water resource loss due to leaks during power station operation.
• Material Adaptability and Corrosion Resistance: GARLOCK offers gaskets made from various materials. For example, PTFE gaskets with anti-creep properties are suitable for sealing pipeline flanges in highly corrosive/chemical environments. This material diversity allows the JNHPP project to select the most appropriate gasket for different fluid media (e.g., cooling water, lubricating oil, or treated chemical water), ensuring long-term chemical stability and avoiding leaks caused by gasket corrosion failure.
• Safety and Environmental Protection: As a well-known brand, GARLOCK products comply with stringent international environmental standards. This means that using GARLOCK gaskets in important infrastructure projects like JNHPP not only ensures equipment safety but also aligns with the modern engineering ethos of environmental responsibility.

During the installation phase of the JNHPP project, selecting the appropriate GARLOCK gaskets (e.g., spiral wound gaskets for high-pressure high-temperature systems, non-metallic gaskets for conventional water systems) and installing them according to specifications can significantly enhance the reliability of flange connections, reduce maintenance needs, and provide a critical safety barrier for the long-term stable operation of the entire power station.

6 Advantages of Ductile Iron Fittings

In the Julius Nyerere Hydropower Project (JNHPP), ductile iron fittings (100MM-650MM), while perhaps not as prevalent as steel pipes in high-pressure main pipelines, demonstrate unique and irreplaceable value in specific systems and scenarios, particularly in plant drainage systems, auxiliary water systems, and underground water conveyance pipelines.

The essence of ductile iron is cast iron treated with nodulizing, which spheroidizes the internal graphite, dramatically improving the material’s mechanical properties. It combines the corrosion resistance of cast iron with strength and toughness approaching that of steel. This allows ductile iron fittings to easily withstand the immense pressures during long-distance conveyance and effectively resist soil compression and deformation.

• Excellent Anti-Corrosion Performance and Durability: Ductile iron fittings are typically treated with advanced anti-corrosion methods, such as cement mortar lining and zinc coating with asphalt paint exterior protection. This combination provides excellence corrosion protection. It makes them particularly suitable for the underground corrosive environment and water corrosion potentially encountered in the JNHPP project, ensuring the piping system has a service life of 50 years or even longer, matching the power station’s design life.
• Outstanding Joint Performance and Seismic Resistance: The T-type socket interface widely used in ductile iron pipelines is a flexible connection method. This interface allows for deflection within a certain angle and can withstand some end displacement, enabling it to effectively adapt to foundation settlement, thermal expansion and contraction caused by temperature changes, and minor geological vibrations. For a large project like JNHPP that may face geological movements or need to traverse different geological conditions, this characteristic is crucial, as it can avoid pipeline rupture caused by rigid connection failure.
• Economy and Ease of Installation: From a full lifecycle cost perspective, ductile iron fittings offer significant cost-effectiveness. Their material and manufacturing costs are relatively low, and the installation of flexible push-on joints is very convenient, which can significantly shorten the construction period and reduce construction costs. Under general terrain conditions, ductile iron pipes require no special foundation treatment, further saving costs and time.

Therefore, in the JNHPP project, ductile iron fittings, with their good durability, excellent ability to adapt to deformation, economical overall cost, and efficient construction, serve as an ideal choice for specific application scenarios, contributing significant value to the power station’s reliable operation and cost control.

7 Comprehensive Application and Recommendations

In a vast and complex engineering project like the Julius Nyerere Hydropower Project (JNHPP), no single piping material or fitting is a universal solution. The key to success lies in selecting the most suitable material for each working condition based on different system operating pressures, media characteristics, environmental conditions, and cost considerations, and integrating them organically into an efficient and reliable overall piping system.

• Synergistic Application and System Optimization: The JNHPP piping system requires a comprehensive selection strategy. For example, in extremely high-pressure, high-risk areas like turbine inlets, seamless steel pipes (SMLS) should be used alongside forged flanges, high-strength butt-weld fittings, and GARLOCK spiral wound gaskets to form the highest level of safety barrier. For medium-low pressure, large-diameter pipelines such as plant drainage systems and circulating water systems, using welded steel pipes (e.g., SAW pipes) or ductile iron pipes with corresponding flanges or push-on joints can significantly optimize project costs while ensuring reliability. This graded, on-demand configuration strategy ensures the best balance between safety and economy for the project.
• Quality Control and Installation Specifications: Even the most superior materials require standardized installation and strict quality control to realize their full potential. For the JNHPP project, the following measures must be strictly implemented:
  • Material Certification: Ensure all pipes, fittings, flanges, and gaskets provide qualified Material Test Certificates (MTC) and Certificates of Conformity, and undergo incoming reinspection as required.
  • Welding Process Control: Conduct strict Welding Procedure Qualifications (WPS/PQR) for all welding operations (especially BW fittings and welded pipes), and employ certified welders holding valid qualifications.
  • Non-Destructive Testing (NDT): Perform Radiographic Testing (RT) or Ultrasonic Testing (UT) on critical welds (e.g., butt welds in high-pressure pipelines) to ensure internal weld quality.
  • Flanged Connection Management: Standardize the bolt tightening sequence and torque values for flanges to ensure even gasket loading and achieve perfect sealing, avoiding leaks caused by improper installation.
• Full Lifecycle Cost Consideration: When selecting piping materials and connection methods, one should not only consider the initial procurement cost but also focus on the project’s full lifecycle cost. For instance, forged components and high-performance gaskets, although requiring higher initial investment, offer extremely long service life and very low failure rates, avoiding expensive downtime and repair losses, often proving more economical in the long run. Similarly, the durability and maintenance-free characteristics of ductile iron pipes also give them excellent long-term cost-effectiveness.

Through the complementary advantages and synergistic application of materials such as welded/SMLS pipes, BW fittings, forged flanges, forged fittings, GARLOCK gaskets, and ductile iron fittings, the Julius Nyerere Hydropower Project (JNHPP) has built a safe, efficient, reliable, and economical piping system. This lays a solid foundation for the long-term stable operation of this significant hydropower station and provides valuable material selection and integration experience for future large-scale hydropower projects.