Pipe Trenchless Rehabilitation: Stainless Steel Sliplining Technology Detailed Explanation

I. Technical Overview and Application Background

1.1 Development History and Principles of Stainless Steel Sliplining

Stainless steel sliplining is an advanced trenchless pipeline rehabilitation technology that inserts thin-walled stainless steel pipes or welded stainless steel plates into existing pipelines to form a "pipe-in-pipe" composite structure. This technology aims to enhance pipeline pressure-bearing capacity, improve corrosion resistance, and extend service life (1). The technique originated in the 1990s and has gradually matured with the development of stainless steel material processing technology and welding techniques, becoming an important method in the field of pipeline rehabilitation worldwide (1).

The basic principle of stainless steel sliplining involves utilizing the excellent physical and chemical properties of stainless steel materials. Through specialized processes, the stainless steel lining is closely bonded to the existing pipeline, creating an integrated composite pipeline system (1). The lining stainless steel layer not only withstands internal fluid pressure but also effectively resists external corrosive media, while maintaining the pipeline's flow capacity (1).

1.2 Technical Advantages and Application Scope

Stainless steel sliplining offers significant advantages over traditional excavation repair methods:

1. Trenchless Construction: No need for full-line excavation; only work pits at both ends of the pipeline are required, minimizing impact on traffic and the surrounding environment (1).
2. Excellent Structural Performance: Forms a composite pipeline with high strength, high sealing performance, and excellent corrosion resistance (1).
3. Long Service Life: The stainless steel lining can last 50 years or more, extending the overall service life when combined with the original pipeline (1).
4. Strong Adaptability: Suitable for rehabilitating pipelines of various materials with diameters ranging from DN200 to DN3000 (1).
5. Short Construction Period: Single construction length can reach more than 300 meters, significantly reducing rehabilitation time (1).
6. Environmental Protection and Energy Saving: Reduces excavation-generated waste and lowers energy consumption (1).

This technology is primarily suitable for:

• Water supply and drainage pipelines suffering from severe corrosion and wear
• Pipelines requiring increased pressure-bearing capacity
• Pipelines in industries with high water quality requirements such as food and pharmaceuticals
• Pipelines under urban main roads where large-scale excavation is not feasible
• Pipelines crossing special sections such as rivers and railways

1.3 Material Selection and Performance Requirements

The main materials used in stainless steel sliplining are stainless steel plates or pipes, with commonly used materials being 304 or 316L austenitic stainless steel. These materials possess the following excellent properties:

1. Corrosion Resistance: Containing more than 18% chromium, they form an extremely thin chromium oxide film on the surface, preventing further metal oxidation (1).
2. High Strength: Tensile strength can reach 520MPa, and yield strength is 210MPa, capable of withstanding high internal pressure (1).
3. Good Weldability: Facilitates welding operations inside pipelines to form a complete lining layer (1).
4. Smooth Inner Wall: Low friction coefficient, 不易 scaling, reducing fluid resistance (1).
5. Hygienic and Non-Toxic: Complies with food hygiene standards, suitable for drinking water pipelines (1).

When selecting materials, comprehensive consideration should be given to factors such as the nature of the medium transported by the pipeline, working pressure, and temperature. Higher-grade stainless steel materials or surface treatments may be selected when necessary.

II. Construction Process Details of Stainless Steel Sliplining

2.1 Pre-construction Preparation Work

Before implementing stainless steel sliplining construction, the following preparation work needs to be completed:

1. Site Investigation and Pipeline Inspection:
   • Conduct geological surveys of the rehabilitation area to understand soil conditions and groundwater level situations.
   • Use CCTV inspection systems to thoroughly examine the internal condition of pipelines, identifying the location and extent of defects.
   • Measure the actual internal diameter of the pipeline to provide a basis for stainless steel lining design (1).
2. Work Pit Excavation:
   • According to design requirements, excavate work pits at appropriate positions at both ends of the pipeline, with dimensions typically 2m×3m.
   • Work pits should avoid other underground pipelines and obstacles, with proper safety protection and drainage measures in place.
   • Support work pits to ensure construction safety (1).
3. Pipeline Preprocessing:
   • Clean the inside of the pipeline to remove dirt, rust, and debris.
   • Repair sharp protrusions and cracks inside the pipeline, and carry out local reinforcement if necessary.
   • Dry the inside of the pipeline to ensure welding quality (1).
4. Material and Equipment Preparation:
   • Customize stainless steel plates or pipes according to pipeline size and design requirements.
   • Prepare specialized equipment such as argon arc welders, plate rolling machines, pipe expanders, and transportation trolleys.
   • Inspect the quality of welding materials and shielding gases to ensure compliance with requirements (1).

2.2 Main Construction Processes and Workflow

There are two main construction processes for stainless steel sliplining: diameter reduction method and internal forming method. The specific choice should be determined based on pipeline diameter, site conditions, and rehabilitation requirements.

2.2.1 Diameter Reduction Method Construction Process

The diameter reduction method is suitable for pipeline rehabilitation with DN200-DN1400, and the main workflow is as follows:

1. Stainless Steel Pipe Prefabrication: Prefabricate stainless steel pipes in the factory, with their outer diameter slightly smaller than or equal to the inner diameter of the pipeline to be rehabilitated.
2. On-site Connection and Diameter Reduction: Use argon arc welding on-site to connect stainless steel pipes, then perform diameter reduction on the stainless steel pipes through a diameter reduction machine to further reduce their diameter.
3. Traction Insertion: Use a tractor to pull the diameter-reduced stainless steel pipe into the pipeline to be rehabilitated.
4. Expansion and Fitting: Apply pressure to expand the stainless steel pipe to make it closely adhere to the inner wall of the original pipeline.
5. Grouting Treatment: After expansion, grout the interlayer between the stainless steel pipe and the original pipeline to form an integrated composite pipe structure (1).

The characteristics of the diameter reduction method are: stainless steel pipes are prefabricated in the factory, reducing on-site welding work and improving construction efficiency; however, it has certain requirements for the bending radius of pipelines and is not suitable for pipelines with excessive bends.

2.2.2 Internal Forming Method Construction Process

The internal forming method is suitable for rehabilitating large-diameter pipelines above DN800, and the main workflow is as follows:

1. Stainless Steel Plate Cutting: Cut stainless steel plates on-site according to the internal diameter size of the pipeline.
2. Pipe Blank Manufacturing: Roll stainless steel plates into pipe blanks, with each pipe blank typically 2-5 meters in length.
3. Pipe Blank Transportation: Transport pipe blanks into the existing pipeline one section at a time.
4. In-pipe Alignment and Welding: Use manual entry into the pipe to align and weld stainless steel pipe blanks into an integral lining layer.
5. Expansion and Fitting: Use specialized pipe expanders to expand the stainless steel lining to make it closely adhere to the inner wall of the original pipeline.
6. Grouting Treatment: Grout the gap between the stainless steel lining and the original pipeline to form a composite structure (1).

The characteristics of the internal forming method are: can directly handle branch pipes without separate excavation; however, manual welding inside the pipeline results in relatively low construction efficiency and requires high skill levels from construction personnel.

The common workflow for both processes can be summarized as:

 

Work pit excavation → Pipeline inspection and preprocessing → Stainless steel lining manufacturing → Lining insertion or transportation → Lining expansion and welding → Port treatment → Grouting reinforcement → Quality inspection

2.3 Key Technical Operation Points

2.3.1 Stainless Steel Lining Manufacturing

The manufacturing quality of the stainless steel lining directly affects the rehabilitation effect, and the following key points need attention:

1. Material Cutting: Use specialized cutting tools for stainless steel to ensure smooth cutting edges without burrs and notches.
2. Plate Rolling and Forming: Adjust the rollers of the plate rolling machine to control the rolling diameter, ensuring that the pipe blank dimensions meet requirements.
3. Welding Process:
   • Use argon arc welding process, strictly controlling welding current, voltage, and welding speed.
   • Before welding, clean the welding joints and the 5cm range on both sides to remove oil and oxides.
   • Welding materials should be stored, dried, issued, and used in strict accordance with relevant procedures.
   • Argon arc welding should follow the principle of gas supply before arc starting and gas stop after arc extinction, with argon purity not less than 99.9% (1).
4. Weld Quality Control:
   • The weld and heat-affected zone surfaces should be smooth and flat, free of pores, lack of penetration, cracks, slag inclusions, undercuts, and other defects.
   • Longitudinal welds of adjacent pipe blanks should be staggered, with the spacing preferably greater than 200mm.
   • Each plate should overlap by 20-30mm, with the overlapping sequence consistent with the water flow direction (1).

2.3.2 Lining Installation and Expansion

Lining installation and expansion are key steps to ensure the close adhesion of the stainless steel lining to the original pipeline:

1. Lining Transportation: Use specialized transportation trolleys to deliver pipe blanks into the original pipeline, taking care to avoid scratching the lining surface.
2. Positioning and Fixing: Accurately place the pipe blanks in the predetermined position and fix them using temporary support devices.
3. Expansion Operation:
   • Apply pressure evenly using hydraulic or mechanical pipe expanders to make the stainless steel lining closely adhere to the inner wall of the original pipeline.
   • Monitor the deformation of the lining during the expansion process to prevent excessive deformation or local non-adhesion.
   • The distance between tack weld points should be ≤20mm, and the circumferential overlap at the pipe joint should be ≤30mm (1).
4. Port Treatment:
   • Install stainless steel transition plates at the pipe ports to connect the lining with the original pipeline as a whole.
   • For 附属设施 such as exhaust valves, first weld stainless steel washers at the exhaust valve positions, then cut holes in the lining pipe and weld them to the washers to retain the original exhaust valve function (1).

2.3.3 Grouting Reinforcement Process

Grouting reinforcement is an important link to improve the overall performance of composite pipelines:

1. Grouting Material Selection: Choose appropriate grouting materials such as cement-based grouts or chemical grouts according to the pipeline environment and requirements.
2. Grouting Pressure Control: Grouting pressure should not be too high to avoid causing buckling deformation of the stainless steel lining. Water can be filled in the stainless steel lining pipe and maintain appropriate water pressure as support.
3. Grouting Hole Layout: Reasonably arrange grouting holes according to pipeline length and diameter to ensure uniform filling of grout in the gap.
4. Grouting Effect Inspection: After grouting is completed, check the grouting fullness and perform supplementary grouting if necessary (1).

2.4 Quality Inspection and Acceptance Standards

Quality inspection and acceptance of stainless steel sliplining rehabilitation projects should be strictly implemented in accordance with relevant standards:

1. Weld Quality Inspection:
   • Visual Inspection: Weld surfaces should be 平整 without cracks, pores, slag inclusions, and other defects.
   • Non-destructive Testing: When necessary, use penetration testing or radiographic testing to inspect internal weld quality.
   • Welding Procedure Qualification: Conduct according to the current industry standards "Welding Procedure Qualification for Pressure Equipment" NB/T 47014 or "Welding Procedure Qualification for Oil and Gas Metal Pipelines" SY/T 0452 (1).
2. Lining Adhesion Inspection:
   • Use the tapping method to check the adhesion between the lining and the original pipeline, there should be no hollow sound.
   • Use CCTV inspection system to check the lining surface quality and adhesion (1).
3. Pressure Test:
   • Hydrostatic Test: Conduct according to "Water Supply and Drainage Pipeline Engineering Construction and Acceptance Specification" (GB50268-2008), the test pressure should be 1.5 times the working pressure, stabilize the pressure for 30 minutes, and the pressure drop should not exceed 0.02MPa.
   • Pneumatic Test: Suitable for special circumstances, the test pressure and stabilization time should meet relevant standard requirements (1).
4. Anti-corrosion Performance Inspection:
   • Check whether the stainless steel lining surface has scratches, corrosion, and other defects.
   • When necessary, conduct salt spray tests or other corrosion tests to evaluate the corrosion resistance of the lining (1).
5. Final Acceptance:
   • Check all construction records and inspection reports to confirm compliance with design requirements.
   • Conduct final acceptance according to "Technical Specification for Lined (Clad) Stainless Steel Composite Steel Pipe Pipeline Engineering" (CECS 205:2015).
   • Submit complete completion materials, including construction drawings, material certificates, test reports, acceptance records, etc (1).

III. Relevant Domestic and Foreign Standards and Specifications

3.1 Overview of Main Standard Systems

Currently, China has formed a relatively complete standard system for stainless steel sliplining rehabilitation technology, mainly including the following aspects:

1. Material Standards:
   • "Stainless Steel Welded Pipes for Fluid Transportation" (GB/T 12771)
   • "Corrosion-resistant Alloy Composite Steel Pipes for Fluid Transportation" (GB/T 31940)
   • "Internal Lined or Clad Corrosion-resistant Alloy Composite Steel Pipes for Petroleum and Natural Gas Industries" (GB/T 37701)
2. Engineering Technical Specifications:
   • "Technical Specification for Lined (Clad) Stainless Steel Composite Steel Pipe Pipeline Engineering" (CECS 205:2015)
   • "Technical Specification for Stainless Steel Lining Rehabilitation Engineering of Water Supply Pipelines" (T/CAS 833-2024)
3. Construction and Acceptance Specifications:
   • "Water Supply and Drainage Pipeline Engineering Construction and Acceptance Specification" (GB50268-2008)
   • "Code for Construction and Acceptance of Welding Engineering for Field Equipment and Industrial Piping" (GB50236-2011)
4. Testing and Evaluation Standards:
   • "Technical Specification for Inspection and Evaluation of Urban Drainage Pipelines" (CJJ 181)
   • "Regulations for Periodic Inspection of Pressure Pipelines" (TSG D7005)

These standards standardize various aspects of stainless steel sliplining, including materials, design, construction, and acceptance, providing a technical basis for engineering practice.

3.2 Key Points Analysis of "Technical Specification for Lined (Clad) Stainless Steel Composite Steel Pipe Pipeline Engineering" (CECS 205:2015)

CECS 205:2015 is China's first engineering technical specification specifically for lined stainless steel composite steel pipes, officially implemented on February 1, 2016. The specification is divided into 6 chapters, with main contents including general provisions, terminology, pipes and fittings, design, pipeline installation, inspection and acceptance, etc.

The core key points of this specification include:

1. Scope of Application: Applicable to lined (clad) stainless steel composite steel pipe pipeline engineering with working pressure not exceeding 2.5MPa and working temperature not exceeding 180°C.
2. Material Requirements:
   • The lining stainless steel material should preferably use austenitic stainless steel, such as 0Cr18Ni9 (304), 0Cr17Ni12Mo2 (316), etc.
   • The base steel pipe should comply with relevant national standards, and its quality should meet design requirements (1).
3. Connection Methods:
   • When DN15≤pipe diameter≤DN80, threaded connection is preferred.
   • When DN100≤pipe diameter≤DN150, grooved connection or welding can be used.
   • When the pipe diameter≥DN150, welding connection is generally used (1).
4. Welding Process Requirements:
   • The connection between the pipeline and flange should use stainless steel electrodes for one-time electric welding to form a single austenitic weld.
   • To avoid the decrease in corrosion resistance and toughness caused by carbide precipitation on the grain boundaries when stainless steel is slowly cooled after welding, rapid cooling measures should be taken after welding.
   • When design requires welding procedure qualification, it should be carried out according to the current industry standards "Welding Procedure Qualification for Pressure Equipment" NB/T 47014 or "Welding Procedure Qualification for Oil and Gas Metal Pipelines" SY/T 0452 (1).
5. Anti-corrosion Requirements:
   • The external anti-corrosion of lined stainless steel composite steel pipes should be determined according to the pipeline laying environment, and anti-corrosion coatings such as petroleum asphalt, coal-tar epoxy, and polyethylene adhesive tape can be used.
   • Pipe joint repair and damage repair should use the same anti-corrosion materials and processes as the pipe body (1).

3.3 Interpretation of "Technical Specification for Stainless Steel Lining Rehabilitation Engineering of Water Supply Pipelines" (T/CAS 833-2024)

T/CAS 833-2024 is the latest standard issued in 2024, specifically targeting stainless steel lining rehabilitation engineering for water supply pipelines, providing detailed regulations for design, construction, acceptance, and other aspects.

The main contents of this specification include:

1. Scope of Application: Applicable to stainless steel lining rehabilitation engineering of municipal, industrial, and building water supply pipelines, covering design, construction, acceptance, and other links.
2. Material Requirements:
   • Stainless steel lining materials should comply with the provisions of current national standards and have quality certification documents.
   • The variety, specification, performance, etc., of materials should meet design requirements and relevant standard provisions.
3. Design Key Points:
   • The designed working life of rehabilitated water supply pipelines should not be less than 50 years.
   • The design should consider the impact of temperature changes on the stainless steel lining, and expansion compensation devices should be installed if necessary.
   • For pipelines that may experience negative pressure, measures should be taken to prevent the lining from being sucked flat (1).
4. Construction Process Requirements:
   • Before construction, conduct a comprehensive inspection and evaluation of the pipeline to determine the rehabilitation plan.
   • Pipeline internal preprocessing should thoroughly remove dirt, rust, and debris to ensure the lining closely adheres to the original pipeline.
   • Welding of stainless steel linings should comply with the provisions of current national standards, and weld quality should meet design requirements.
5. Acceptance Standards:
   • The rehabilitated pipeline should undergo a pressure test, with the test pressure being 1.5 times the working pressure.
   • Use a CCTV inspection system to check the lining surface quality and adhesion, which should be free of cracks, pores, slag inclusions, and other defects.
   • Water quality should comply with the provisions of the current national standard "Standards for Drinking Water Quality" (GB 5749) (1).

This specification also provides detailed regulations on project acceptance processes, quality inspection methods, problem rectification and handling, etc., providing comprehensive technical guidance for stainless steel lining rehabilitation engineering of water supply pipelines.

3.4 Construction Safety Specifications and Environmental Protection Requirements

In addition to complying with the above technical standards, stainless steel sliplining rehabilitation projects should also meet the following safety and environmental protection requirements:

1. Construction Safety Specifications:
   • Set up obvious warning signs and protective facilities around work pits, and install warning lights at night.
   • Before entering the pipeline for operations, conduct gas detection to ensure no toxic or harmful gases are present.
   • Lighting inside the pipeline should use safe voltage, with the voltage of portable lamps not exceeding 12V.
   • When welding, take ventilation measures to prevent the accumulation of harmful gases.
   • When working at heights, fasten safety belts and set up safety platforms (1).
2. Environmental Protection Requirements:
   • Construction wastewater should be treated and meet discharge standards before being discharged, and should not be directly discharged into rainwater pipes or rivers.
   • Welding fumes should be treated through purification equipment to reduce air pollution.
   • Construction noise should comply with the provisions of the "Noise Emission Standards for Construction Sites" (GB 12523).
   • Waste stainless steel scraps and welding materials should be classified and recycled, and should not be discarded 随意.
   • Take effective measures to control dust and reduce the impact on the surrounding environment (1).
3. Occupational Health Requirements:
   • Construction personnel should wear personal protective equipment such as protective glasses, masks, and gloves.
   • Regularly conduct occupational health examinations for construction personnel to prevent occupational diseases.
   • Provide necessary heatstroke prevention, cooling, cold protection, and warmth preservation measures to protect the health of construction personnel (1).

IV. Engineering Case Analysis

4.1 Stainless Steel Lining Rehabilitation Project of DN800 Raw Water Pipeline in Fuzhou City

4.1.1 Project Overview

A DN800 raw water pipeline in a water plant in Fuzhou City was built in 1976, with a pipe material of reinforced concrete and a total length of about 2100 meters. It is located in the central area of Fuzhou City, passing through multiple residential areas, rivers, and main roads. Due to its long service life, the pipeline has severely aged, with frequent leaks, seriously affecting water supply safety. Considering that the pipeline is located in the city center with heavy traffic and numerous ground obstacles, if traditional excavation repair methods were used, it would not only be costly and time-consuming but also severely affect the surrounding environment and residents' lives. After comprehensive 论证，the decision was made to use thin-walled stainless steel (304) lining rehabilitation technology for trenchless repair (1).

4.1.2 Technical Solution Implementation

This project adopted the internal forming method construction process, with the main technical solutions as follows:

1. Material Selection: The lining material selected was austenitic 304 stainless steel plate (0Cr18Ni9) with a thickness of 1.2mm, which has excellent corrosion resistance and mechanical properties.
2. Work Pit Setting: According to the actual site conditions, a total of 8 work wells were set up, with the inner wall clear size of each work well being 3.0m×2.2m, and the bottom of the work well being 0.5m below the bottom of the pipeline.
3. Pipeline Preprocessing:
   • Use a CCTV inspection system to comprehensively check the internal condition of the pipeline and determine the location and extent of defects.
   • Use a combination of mechanical and manual methods to clean the pipeline and remove dirt and rust.
   • Chisel off protrusions and sharp corners inside the pipeline to make them smooth; for gaps at joints or cracks, use cement mortar to level them; for parts with local damage and severe water leakage in the pipeline, use steel internal expansion hoops for welding reinforcement (1).
4. Manufacturing and Installation of Stainless Steel Lining:
   • Roll 1.5m wide stainless steel plates into pipe blanks on-site, controlling the rolled diameter within 600mm.
   • Use transportation trolleys to send the pipe blanks into the original pipeline, with each pipe blank section approximately 2-3 meters in length.
   • Use specialized pipe expanders to expand the stainless steel pipe blanks to make the stainless steel pipes closely adhere to the original pipeline.
   • Adopt a staged centralized operation method for in-pipe welding, first completing the layout of more than 100 meters of stainless steel pipe blanks, then centrally conducting longitudinal and circumferential welding (1).
5. Port Treatment: Install steel socket plates on the original pipeline, weld a circle of 100mm wide and 5mm thick stainless steel plates on the socket plate steel pipes, then weld the stainless steel lining pipe to the 5mm thick stainless steel plates to form a metal-sealed whole.
6. Negative Pressure Treatment: Install 6mm thick and 5cm wide stainless steel expansion rings at different high points along the pipeline to reduce the destructive bending of the stainless steel lining when the pipeline 停水；install DN100 high-speed intake and exhaust valves at the positions of the existing excavated work wells to ensure pipeline safety.
7. Thermal Expansion and Contraction Treatment: Considering the water temperature changes in Fuzhou area, install expansion joints for each pipeline section to adapt to the thermal expansion and contraction of the stainless steel lining (1).

4.1.3 Implementation Effect and Experience Summary

This project was successfully completed in 2019 and has been operating well for many years, with the main performance in the following aspects:

1. Significant Economic Benefits:
   • The construction cost of using stainless steel lining repair technology is 1.7 million yuan/km, which is about 42% lower than the 2.943 million yuan/km for newly laying DN800 steel pipes or ductile iron pipes.
   • According to calculations, after lining a DN800 reinforced concrete pipe with 1.2mm austenitic 304 stainless steel, under the condition of constant water outlet pressure from the water intake pump, the water transmission capacity can be increased by 45%; if the current flow rate is maintained, the pump head can be reduced, resulting in a reduction of about 93×10kW·h/a in power consumption (1).
2. Outstanding Social Benefits:
   • Avoided about 15,000m³ of earth excavation and backfilling, reducing the generation of construction waste.
   • The construction period was shortened by about 60% compared to the traditional excavation method, reducing the impact on traffic and residents' lives.
   • Solved the problem of pipeline leakage and improved the safety and reliability of water supply (1).
3. Technical Experience Summary:
   • Stainless steel lining repair technology is particularly suitable for pipeline repair in central urban areas and busy traffic areas.
   • Before construction, existing leakage points must be effectively blocked to ensure the pipe is dry before proceeding with stainless steel welding work.
   • For long-distance pipelines, the impact of temperature changes on the stainless steel lining should be fully considered, and expansion compensation devices should be reasonably installed.
   • The treatment of pipeline elbows is a technical difficulty that requires prefabricating the stainless steel splicing materials for each elbow according to the elbow shape and size, and precisely assembling and welding them inside the pipeline (1).

4.2 Rehabilitation Project of DN800 Water Supply Pipeline on Yanjiang North Road in Zhuzhou City

4.2.1 Project Overview

The DN800 water supply main pipe on Yanjiang North Road in Zhuzhou City is a cement pipe laid in the 1980s, with a total length of 1670 meters, located on Yanjiang North Road in Shifeng District, and is an important water supply main pipe in the city. Due to severe pipeline aging, frequent leaks and bursts have seriously affected the water supply safety of the surrounding areas. Considering that this pipeline is located on a city's main road, if traditional excavation repair methods were used, it would not only be costly and have a significant impact but also affect the city's civilized creation work. After research, the decision was made to adopt the "trenchless stainless steel lining" technology for repair, which is also the first project in Hunan Province's water industry to introduce this technology (1).

4.2.2 Technical Innovation and Implementation

This project adopted the diameter reduction method construction process, with the main technical innovation points as follows:

1. Material Innovation: Adopted thin-walled stainless steel pipes as lining materials, which are not only lightweight and convenient for transportation and installation but also have excellent corrosion resistance and durability.
2. Process Innovation:
   • Adopted the diameter reduction-expansion process, first reducing the diameter of the stainless steel pipe and then pulling it into the original pipeline, and then expanding it through pressure to make it adhere to the inner wall of the original pipeline.
   • Adopted the argon arc welding process for welding inside the pipeline to form a complete lining layer.
   • Conducted special treatment on the pipeline ports, using thick stainless steel transition plates to connect the thin-walled stainless steel lining pipe with the original pipeline as a whole (1).
3. Construction Organization Innovation:
   • Construction from 停水 excavation, pipeline cleaning, CCTV inspection, pushing stainless steel pipe blanks into old pipes, etc., to the final port treatment, pressure testing and other more than 20 processes, were basically carried out manually in the narrow pipe.
   • Adopted a segmented construction method, with each segment about 200-300 meters in length, ensuring construction quality and safety (1).

4.2.3 Implementation Effect and Promotion Value

This project was fully completed on October 27, 2017, and has been operating well for many years:

1. Technical Effect:
   • The rehabilitated pipeline formed a "pipe-in-pipe" composite structure, significantly improving strength and sealing performance.
   • The service life of the stainless steel lining can reach 100 years, and it is expected that the service life of the rehabilitated pipeline will be extended by 50-100 years.
   • The inner wall of the pipeline is smooth, reducing water flow resistance and increasing water transmission capacity by about 30% (1).
2. Social and Economic Benefits:
   • Avoided about 12,000m³ of earth excavation, reducing the impact on urban traffic and the environment.
   • The construction period was shortened by about 50% compared to the traditional excavation method, reducing 停水 time and the impact on residents' lives.
   • Reduced pipeline leakage rate, saved water resources, and improved water supply efficiency (1).
3. Promotion Value:
   • The successful implementation of this project has broken the limitation that the renovation of urban old pipelines, especially the water supply pipeline network of urban main roads, can only be carried out simultaneously with urban road renovation.
   • Provided a new technical option for the rehabilitation of urban underground pipelines, with a good demonstration effect.
   • Promoted the application and popularization of trenchless repair technology in Hunan Province's water industry (1).

4.2 Case Study: Mine Site Stainless Steel Piping Rehabilitation in Australia

4.2.1 Project Background

A mining company in Australia faced significant challenges with its aging pipeline infrastructure, particularly in remote mine site conditions. The existing pipelines were suffering from severe corrosion and required replacement to ensure reliable operation and extend service life (1). The project was part of a $45 million sustaining works program aimed at maintaining operational efficiency and safety in harsh environmental conditions (1).

4.2.2 Technical Approach

The project team selected stainless steel piping as the replacement material due to its exceptional corrosion resistance and durability in challenging environments. Specifically, Victaulic Vic-Press products for stainless steel piping were chosen to provide a high-quality, ASME-compliant piping system (1). The selection process focused on ensuring joint integrity while maximizing the service life of the piping systems, which was crucial in the remote mine site conditions (1).

The project involved the installation of robust, corrosion-resistant stainless steel piping throughout the mine site, addressing the challenges posed by the harsh operating environment. The selected materials and connection methods were chosen to withstand the rigors of mining operations while meeting strict compliance standards (1).

4.2.3 Implementation Results and Lessons Learned

The implementation of the stainless steel piping system demonstrated several key benefits:

1. Enhanced Durability: The stainless steel piping system showed significantly improved resistance to corrosion and wear compared to the previously used materials, extending the expected service life of the pipelines (1).
2. Improved Safety: The ASME-compliant system provided enhanced structural integrity, reducing the risk of leaks and failures in remote locations where access and repair can be challenging (1).
3. Reduced Maintenance Needs: The corrosion-resistant properties of the stainless steel material led to a substantial reduction in maintenance requirements, lowering long-term operational costs (1).
4. Compliance Assurance: The use of Victaulic Vic-Press products ensured compliance with industry standards, providing confidence in the system's performance and safety (1).

This case study highlights the successful application of stainless steel piping systems in demanding industrial environments, demonstrating the technology's ability to deliver reliable, long-lasting solutions in challenging conditions.

4.3 Comparison of Domestic and Foreign Cases

The following table compares the key characteristics of the domestic and foreign stainless steel piping rehabilitation cases discussed:

 

Case Characteristic	Fuzhou DN800 Water Pipeline	Zhuzhou DN800 Water Pipeline	Australian Mine Site Piping
Pipeline Diameter	DN800	DN800	Varies (not specified)
Pipe Material	Reinforced concrete	Cement	Not specified
Lining Material	304 stainless steel (1.2mm)	Thin-walled stainless steel	Stainless steel (type not specified)
Construction Method	Internal forming method	Diameter reduction method	Not specified
Project Duration	Completed in 2019	Completed in October 2017	Completed in 2022
Main Challenges	Urban environment, heavy traffic	City main road, urban civilization creation	Harsh environmental conditions, remote location
Key Benefits	42% cost savings, 45% flow increase	50% shorter construction period, 30% flow increase	Enhanced durability, reduced maintenance, compliance assurance
Special Features	Negative pressure and thermal expansion compensation measures	First application in Hunan water industry	ASME-compliant system, Victaulic Vic-Press connections

This comparison illustrates the versatility of stainless steel lining technology across different environments and project requirements, from urban water supply systems to remote industrial applications.

V. Comparison and Analysis with Other Trenchless Rehabilitation Technologies

5.1 Overview of Main Trenchless Rehabilitation Technologies

Currently, the commonly used pipeline trenchless rehabilitation technologies in China mainly include the following types:

1. Cured-in-Place Pipe (CIPP):
   • Impregnate fiberglass hoses with resin, then insert them into the pipeline to be rehabilitated through pulling and other methods. Inflate the hoses to make them adhere to the inner wall of the pipeline, and then use ultraviolet light or hot water to rapidly cure the resin to form a new lining pipe that closely adheres to the original pipeline.
   • Mainly divided into three types: hot water curing, steam curing, and ultraviolet light curing (7).
2. FIPP Thermoplastic Molding Method:
   • Use thermoplastic materials as internal support for prefabricated lining materials, and through heating and pressurization, expand them to adhere to the inner wall of the original pipeline, eventually forming a rigid pipeline.
   • Has the advantages of simple construction process and low labor cost (7).
3. Stainless Steel Quick Lock Lining Method:
   • Form a layer of 坚固 protective layer by lining stainless steel materials on the original pipeline, effectively preventing pipeline deformation and corrosion.
   • The construction process is transparent, with minimal interference to the lives of surrounding residents (7).
4. HDPE Pipe Sliplining Method:
   • Insert HDPE pipes with an outer diameter slightly smaller than the inner diameter of the original pipeline into the original pipeline through traction or jacking, forming a "pipe-in-pipe" structure.
   • Suitable for pipeline rehabilitation with DN150-DN1200, with fast construction speed and low cost (7).
5. Spiral Winding Method:
   • Spiral wind strip-shaped profiles inside the original pipeline into a continuous tubular lining, connecting through special locking or welding methods.
   • Suitable for pipeline rehabilitation with DN300-DN2000, can form a continuous lining layer inside the pipeline (7).
6. Spot In-situ Resin Curing Method:
   • For local defects in pipelines, use resin-impregnated fiberglass cloth to perform local curing repair at the defect locations.
   • Suitable for repairing local cracks, corrosion, and other defects in pipelines (7).

5.2 Comparative Analysis of Technical Performance

The technical performance comparison of various trenchless rehabilitation technologies is shown in the following table:

 

Technical Indicator	Stainless Steel Sliplining	CIPP UV Curing	FIPP Thermoplastic Molding	HDPE Sliplining	Spiral Winding
Applicable Pipe Diameter	DN200-DN3000	DN100-DN2000	DN200-DN2600	DN150-DN1200	DN300-DN2000
Applicable Pipe Materials	All types	Concrete, cast iron, steel, etc.	Concrete, cast iron, corrugated pipe, etc.	Metal pipes, concrete pipes, etc.	Concrete, brick pipes, etc.
Rehabilitation Type	Structural/Semi-structural	Structural	Semi-structural	Structural/Non-structural	Structural/Non-structural
Construction Period	Longer	Short (several hours)	Shorter	Short	Longer
Service Life	Over 50 years	40-50 years	Over 20 years	30-50 years	30-50 years
Pressure-bearing Capacity	High	High	Medium-high	Medium	Medium
Corrosion Resistance	Excellent	Good	Good	Good	Good
Internal Wall Roughness	Extremely low (smooth)	Low	Low	Low	Lower
Interface Treatment	Welding, good integrity	Needs special treatment	Needs special treatment	Mechanical connection	Spiral lock or welding
Branch Pipe Treatment	Needs separate treatment (internal forming method can directly handle)	Needs special treatment	Needs special treatment	Needs special treatment	Needs special treatment
Construction Space Requirements	Larger work pit size	Smaller work pit size	Smaller work pit size	Smaller work pit size	Larger work pit size
Adaptability to Pipeline Deformation	Good	Excellent	Excellent	General	General

From the technical performance comparison:

1. Application Range: Stainless steel sliplining has the broadest applicable pipe diameter range, from DN200 to DN3000, and strong adaptability to pipe material types; CIPP UV curing method has relatively smaller applicable pipe diameter, but the strongest adaptability to pipeline deformation.
2. Rehabilitation Effect: Both stainless steel sliplining and CIPP UV curing methods have the best structural rehabilitation effect, which can significantly improve the pressure-bearing capacity and service life of pipelines; FIPP thermoplastic molding method and HDPE sliplining method are suitable for semi-structural or non-structural rehabilitation.
3. Construction Characteristics: CIPP UV curing method has the shortest construction period, usually completing in several hours; stainless steel sliplining has a longer construction period, especially the internal forming method requires manual welding operations inside the pipeline.
4. Service Life: Stainless steel sliplining has the longest service life, up to more than 50 years; the service life of other methods is mostly between 30-50 years.
5. Interface Treatment: Stainless steel sliplining forms an integral lining through welding, with the most reliable interface treatment; other methods mostly use mechanical connections or special treatment methods, which may have weak points at the interfaces.

5.3 Comparative Analysis of Economic Efficiency

The economic efficiency comparison of various trenchless rehabilitation technologies is shown in the following table:

 

Technical Type	Price per Meter (RMB)	Material Cost (RMB/m)	Labor Cost (RMB/m)	Equipment Cost (RMB/m)	Comprehensive Cost (10,000 RMB/50m)
Stainless Steel Sliplining	170-957	100-600	50-200	20-157	3.0-7.0
CIPP UV Curing	88.88-1200	400-800	200-400	88.88-200	3.0-7.0
FIPP Thermoplastic Molding	100.00	300-500	100-200	100.00	2.5-5.0
HDPE Sliplining	150-300	200-400	100-200	50-100	2.0-4.0
Spiral Winding	200-400	300-500	150-300	50-100	3.0-6.0

From the economic efficiency comparison:

1. Direct Cost: HDPE sliplining method and FIPP thermoplastic molding method have relatively lower comprehensive costs, especially for short-distance rehabilitation; stainless steel sliplining method has higher material costs, but longer service life, and better economic efficiency in the long term.
2. Cost Composition: CIPP UV curing method has the highest material cost, especially imported materials; stainless steel sliplining method has higher labor costs, especially the internal forming method requires professional welders to operate inside the pipeline; FIPP thermoplastic molding method has relatively lower equipment costs.
3. Scale Effect: For long-distance pipeline rehabilitation, the unit cost of stainless steel sliplining method and CIPP UV curing method can be reduced by 15-25%; for short-distance or local rehabilitation, HDPE sliplining method and spot in-situ resin curing method are more economical.
4. Comprehensive Benefits: Although the initial investment of stainless steel sliplining is higher, due to its long service life, low maintenance cost, and high water transmission efficiency, its full life cycle cost is the lowest; the comprehensive benefits of CIPP UV curing method are second.

5.4 Comparative Analysis of Application Scenarios

The application scenarios comparison of various trenchless rehabilitation technologies is as follows:

 

Technical Type	Most Suitable Application Scenarios	Least Suitable Application Scenarios	Special Application Advantages
Stainless Steel Sliplining	Large-diameter pipelines, high-pressure pipelines, drinking water pipelines, severely corroded pipelines	Small-diameter pipelines (DN<200), severely deformed pipelines	Can improve pipeline pressure-bearing capacity, suitable for occasions with high water quality requirements
CIPP UV Curing	Pipelines of various materials, complex pipelines, curved pipelines, emergency repairs	Severely deformed pipelines, large amounts of sediment, high-temperature environments	Fast construction speed, good lining integrity, wide application range
FIPP Thermoplastic Molding	Concrete pipes, cast iron pipes, double-wall corrugated pipes, etc., medium-diameter pipelines	Severely deformed pipelines, pipelines with sharp protrusions, high-temperature environments	Simple construction process, low labor cost
HDPE Sliplining	Small and medium-diameter pipelines, pipelines with more straight sections, occasions with high water quality requirements	Large-diameter pipelines, curved pipelines, severely deformed pipelines	Fast construction speed, lower cost, can operate with water
Spiral Winding	Large-diameter pipelines, special-shaped pipelines, non-circular pipelines, long-distance pipelines	Small-diameter pipelines, pipelines with small bending radii, pipelines with obstacles	Can form continuous lining, adapt to non-circular pipelines
Spot In-situ Resin Curing	Local defects in pipelines, small-scale repairs, occasions with strict maintenance cost constraints	Extensively damaged pipelines, structurally severely damaged pipelines	Low local repair cost, simple construction

From the application scenarios comparison:

1. Stainless Steel Slipliningis particularly suitable for drinking water pipelines with high water quality requirements, large-diameter pipelines, pipelines requiring increased pressure-bearing capacity, and severely corroded pipelines; its application is limited in small-diameter pipelines and severely deformed pipelines.
2. CIPP UV Curinghas the broadest application range, almost suitable for the rehabilitation of all types of pipelines, especially for situations with urgent construction time requirements and complex pipeline shapes; however, it has high requirements for pipeline internal cleanliness and is not suitable for pipelines with severe deformation or large amounts of sediment.
3. FIPP Thermoplastic Moldingis suitable for the rehabilitation of medium-diameter concrete pipes, cast iron pipes, and double-wall corrugated pipes, with the advantages of simple construction process and low labor cost; however, it is more sensitive to pipeline deformation and sharp protrusions.
4. HDPE Slipliningis suitable for small and medium-diameter, straight-section pipelines with fast construction speed and lower cost; however, its application is limited in large-diameter pipelines, curved pipelines, and severely deformed pipelines.
5. Spiral Windingis particularly suitable for the rehabilitation of large-diameter pipelines, special-shaped pipelines, and non-circular pipelines, which can form continuous lining layers; however, its construction speed is slow, and its adaptability to pipelines with small bending radii is poor.
6. Spot In-situ Resin Curingis suitable for the repair of local defects in pipelines, with low cost and simple construction; however, it is not suitable for extensively damaged or structurally severely damaged pipelines.

5.5 Comprehensive Evaluation and Selection Recommendations

Based on the above comparative analysis, the comprehensive evaluation and selection recommendations for various trenchless rehabilitation technologies are as follows:

1. Technology Selection Principles:
   • Comprehensive consideration should be given to factors such as pipeline material, diameter, damage extent, service environment, and rehabilitation requirements.
   • The applicability, reliability, economy, and environmental protection of the technology should be considered, and multiple schemes should be compared.
   • The technical strength and experience of the construction unit should be combined to select the most assured technical scheme.
2. Optimal Selection Under Different Scenarios:
   • Drinking Water Pipelines: Give priority to stainless steel sliplining and CIPP UV curing to ensure water quality safety.
   • Sewage Pipelines: Consider CIPP UV curing, FIPP thermoplastic molding, or HDPE sliplining, and select according to pipeline conditions and budget.
   • Large-diameter Pipelines (DN≥800): Give priority to stainless steel sliplining or spiral winding to ensure structural reliability.
   • Small and Medium-diameter Pipelines (DN<800): Can consider CIPP UV curing, FIPP thermoplastic molding, or HDPE sliplining.
   • Curved Pipelines: Give priority to CIPP UV curing, whose flexible lining can adapt to complex pipeline shapes.
   • Severely Corroded Pipelines: Give priority to stainless steel sliplining or CIPP UV curing to ensure corrosion resistance.
   • Emergency Repairs: Give priority to CIPP UV curing or spot in-situ resin curing, with fast construction speed.
   • Budget Constraints: Can consider HDPE sliplining or FIPP thermoplastic molding, with relatively lower costs.
3. Technology Combination Application:
   • In practical engineering, according to the damage extent of different parts of the pipeline, multiple technologies can be combined for application.
   • For example, use stainless steel sliplining or CIPP UV curing for overall repair of the main pipeline, and use spot in-situ resin curing for strengthening treatment of local severe defects.
   • For parts with branch pipes, the internal forming process of stainless steel sliplining can be used for treatment to avoid additional excavation.
4. Future Development Trends:
   • With the development of materials science and manufacturing technology, stainless steel sliplining will develop towards thinner walls, higher strength, and better corrosion resistance.
   • CIPP UV curing will develop towards faster curing, higher strength, and lower shrinkage rate, improving repair quality and efficiency.
   • Various trenchless rehabilitation technologies will become more intelligent and automated, reducing manual operations and improving construction accuracy and safety.
   • The combined application of multiple technologies will become a trend to adapt to complex pipeline rehabilitation needs.

VI. Technical Development Trends and Prospects

6.1 Development Directions of Material Innovation

Material innovation for stainless steel sliplining mainly focuses on the following directions:

1. High-performance Stainless Steel Materials:
   • Develop higher-strength, higher-corrosion-resistance stainless steel materials such as duplex stainless steel and super austenitic stainless steel to improve the service life and performance of linings.
   • Research surface treatment technologies such as coatings and platings to further improve the corrosion resistance and wear resistance of stainless steel.
   • Develop stainless steel materials with better weldability to reduce on-site welding difficulty and improve welding quality.
2. Composite Reinforced Materials:
   • Research the combined application of stainless steel with carbon fiber, glass fiber, and other composite materials to improve the strength and toughness of linings.
   • Develop stainless steel-polymer composite lining materials that combine the high strength of stainless steel with the corrosion resistance of polymers.
   • Research nanomaterial-reinforced stainless steel composite materials to improve the comprehensive performance of materials.
3. Environmentally Friendly Materials:
   • Develop recyclable stainless steel materials to reduce resource waste and environmental pollution.
   • Research low-energy-consumption, low-emission stainless steel production processes to reduce carbon footprint.
   • Develop stainless steel lining materials that are pollution-free to water quality to meet higher drinking water hygiene standards.

6.2 Innovation Trends in Process Technology

Process technology innovation for stainless steel sliplining is mainly reflected in the following aspects:

1. Automated Welding Technology:
   • Develop automatic welding equipment inside pipelines to reduce manual operations and improve welding quality and efficiency.
   • Research robotic welding technology to achieve high-precision welding in complex environments.
   • Apply advanced welding technologies such as laser welding and electron beam welding to improve welding quality and speed.
2. Intelligent Lining Installation Technology:
   • Develop automatic lining positioning and expansion systems to improve installation accuracy and efficiency.
   • Research lining adhesion detection technology based on sensors to monitor installation quality in real-time.
   • Apply digital twin technology to visualize and digitally manage the lining installation process.
3. New Connection Technologies:
   • Develop mechanical connection technologies that eliminate the need for welding, simplifying construction processes and reducing construction difficulty.
   • Research self-sealing connection technologies to improve the sealing performance and reliability of interfaces.
   • Develop quick connection technologies to shorten construction periods and reduce water shutoff time.
4. Trenchless Branch Pipe Connection Technology:
   • Research trenchless connection technologies between lining pipes and branch pipes to reduce excavation work.
   • Develop automatic branch pipe positioning and connection systems to improve connection accuracy and efficiency.
   • Research branch pipe connection tools that can operate inside pipelines to avoid external excavation.

6.3 Digital and Intelligent Development Trends

The digital and intelligent development of stainless steel sliplining is mainly reflected in the following aspects:

1. Pipeline Detection and Evaluation Technology:
   • Develop high-precision pipeline detection equipment such as 3D laser scanning and ultrasonic testing to improve the accuracy of defect identification.
   • Research pipeline defect analysis systems based on artificial intelligence to automatically identify and evaluate pipeline conditions.
   • Develop pipeline health monitoring systems to monitor pipeline operating status in real-time and predict potential problems.
2. Digital Design and Simulation Technology:
   • Develop digital design platforms for stainless steel sliplining rehabilitation projects to achieve parametric design and optimization.
   • Research finite element analysis technology to simulate the stress state of linings under different working conditions and optimize design schemes.
   • Apply digital twin technology to establish virtual models of pipelines and linings for full lifecycle management.
3. Intelligent Construction Management Technology:
   • Develop construction process management systems to monitor construction progress, quality, and safety in real-time.
   • Research remote monitoring systems for construction equipment based on the Internet of Things to improve construction efficiency and safety.
   • Develop construction quality traceability systems to achieve traceable management of the entire construction process.
4. Big Data and Artificial Intelligence Applications:
   • Establish a database of pipeline rehabilitation cases and apply big data analysis technology to provide decision support for rehabilitation schemes.
   • Research optimization algorithms for rehabilitation schemes based on artificial intelligence to automatically generate and optimize rehabilitation schemes.
   • Develop intelligent early warning systems to conduct long-term monitoring and early warning of rehabilitated pipelines.

6.4 Market Application Prospect Outlook

As an advanced trenchless rehabilitation technology, stainless steel sliplining has broad market application prospects, mainly reflected in the following aspects:

1. Growth in Market Demand:
   • With the aging of urban infrastructure in China, pipeline rehabilitation demand will continue to grow, with the market size expected to grow at an average annual rate of 15% over the next 5 years.
   • Increased requirements for drinking water safety and environmental protection will promote the application of stainless steel sliplining in drinking water pipeline rehabilitation.
   • The tension in urban underground space resources and restrictions on environmental impact will promote the widespread application of trenchless rehabilitation technologies.
2. Expansion of Application Areas:
   • Applications in industrial pipelines will expand, such as the rehabilitation of corrosive medium pipelines in chemical, petroleum, power, and other industries.
   • Applications in special environments will expand, such as submarine pipelines, high-temperature pipelines, high-pressure pipelines, etc.
   • Applications in newly constructed pipelines will increase, such as using linings in newly constructed pipelines to improve their service life and performance.
3. Expansion of Regional Markets:
   • Expansion from first-tier cities to second and third-tier cities, especially in the transformation of old urban areas and the process of urbanization.
   • Applications in central and western regions will increase as infrastructure construction in these regions accelerates.
   • Market opportunities in countries along the "Belt and Road" will expand, promoting the export of Chinese technology and equipment.
4. Industrial Chain Development:
   • Upstream material and equipment manufacturers will increase R&D investment to improve product quality and performance.
   • Midstream construction enterprises will develop towards specialization and scale, improving technical levels and service capabilities.
   • Downstream testing, design, consulting, and other services will become more complete, forming a complete industrial chain.
5. Policy Support and Promotion:
   • National policy support for infrastructure construction and environmental protection will promote the development of the pipeline rehabilitation market.
   • Encouragement policies for trenchless technology will promote the application of advanced technologies such as stainless steel sliplining.
   • Attention to drinking water safety will promote the application of stainless steel sliplining in drinking water pipelines.

VII. Conclusions and Recommendations

7.1 Comprehensive Technical Evaluation

Stainless steel sliplining, as an advanced trenchless pipeline rehabilitation technology, has the following significant characteristics:

1. Obvious Technical Advantages:
   • The formed "pipe-in-pipe" composite structure has excellent structural performance and corrosion resistance, which can significantly improve the pressure-bearing capacity and service life of pipelines.
   • Trenchless construction has little impact on traffic and the surrounding environment, especially suitable for pipeline rehabilitation in central urban areas and busy traffic areas.
   • Wide application range, suitable for rehabilitating pipelines of various materials with diameters from DN200 to DN3000, with strong adaptability.
   • The lining surface is smooth, not easy to scale, which can reduce fluid resistance and improve water transmission efficiency.
   • Long service life, up to more than 50 years, reducing the cost and trouble of frequent repairs.
2. Technical Limitations:
   • The construction process is relatively complex, with high technical requirements for construction personnel, especially the difficulty of on-site welding quality control.
   • Longer construction period, especially for large-diameter pipelines and long-distance pipeline rehabilitation.
   • Higher initial investment, larger one-time input, with greater financial pressure.
   • High requirements for pipeline internal preprocessing, requiring thorough removal of dirt and rust.
   • Has certain requirements for pipeline deformation and ovality, not suitable for severely deformed pipelines.
3. Significant Comprehensive Benefits:
   • Although the initial investment is high, from a full lifecycle perspective, the comprehensive cost is lower than traditional excavation repair methods.
   • Improves pipeline water transmission efficiency, reduces energy consumption, and has significant energy-saving and emission-reduction effects.
   • Reduces the impact of excavation on urban traffic and the environment, with good social benefits.
   • Extends pipeline service life, reducing the social impact and economic losses caused by frequent repairs.

7.2 Engineering Application Recommendations

Based on the above analysis, recommendations for the engineering application of stainless steel sliplining are as follows:

1. Technology Selection Recommendations:
   • For drinking water pipelines, large-diameter pipelines, pipelines requiring increased pressure-bearing capacity, and severely corroded pipelines, give priority to considering the use of stainless steel sliplining.
   • When selecting stainless steel sliplining, according to pipeline diameter, site conditions, and rehabilitation requirements, reasonably select the diameter reduction method or internal forming method.
   • For small-diameter pipelines (DN<200), severely deformed pipelines, or projects with limited budgets, other trenchless rehabilitation technologies can be considered.
2. Design and Construction Recommendations:
   • Before rehabilitation, comprehensively inspect and evaluate the pipeline to determine the location and extent of defects, providing a basis for design.
   • According to the working environment and medium characteristics of the pipeline, reasonably select the type and thickness of stainless steel materials.
   • Fully consider the impact of temperature changes on the stainless steel lining, and reasonably install expansion compensation devices.
   • For pipelines that may experience negative pressure, take measures to prevent the lining from being sucked flat.
   • Strengthen quality control during construction, especially the control of welding quality and lining adhesion.
3. Quality Control Recommendations:
   • Strictly implement relevant standards and specifications to ensure material quality and construction quality.
   • Strengthen the training and assessment of construction personnel to ensure they have the corresponding technical capabilities.
   • Improve quality inspection methods and strictly inspect key links such as weld quality, lining adhesion, and pressure testing.
   • Establish a complete quality traceability system to ensure the entire construction process is traceable.
4. Safety and Environmental Protection Recommendations:
   • Strengthen safety management at the construction site, especially safety control for confined space operations.
   • Take effective measures to control construction noise, dust, and waste to reduce the impact on the surrounding environment.
   • Strengthen the control of welding fumes and harmful gases to protect the occupational health of construction personnel.
   • Construction wastewater should be treated and meet discharge standards before being discharged to avoid polluting the environment.

7.3 Future Development Recommendations

To promote the further development of stainless steel sliplining, the following recommendations are proposed:

1. Technology Innovation Recommendations:
   • Strengthen research and development of high-performance stainless steel materials to improve material strength, corrosion resistance, and weldability.
   • Research automated welding technology and intelligent installation technology to improve construction efficiency and quality.
   • Develop new connection technologies and branch pipe treatment technologies to simplify construction processes and reduce construction difficulty.
   • Strengthen the application of digital and intelligent technologies in pipeline rehabilitation to improve design, construction, and management levels.
2. Standardization Recommendations:
   • Further improve the standard system for stainless steel sliplining and formulate more detailed technical standards and construction guidelines.
   • Strengthen alignment with international standards to enhance the international influence of China's pipeline rehabilitation technology.
   • Develop technical guidelines for different application scenarios to provide more specific guidance for engineering practice.
3. Industry Development Recommendations:
   • Foster specialized pipeline rehabilitation enterprises to improve the overall technical level and service capabilities of the industry.
   • Strengthen industry-university-research cooperation to promote technological innovation and 成果
   • Establish industry exchange platforms to promote technical experience exchange and resource sharing.
   • Promote industry self-discipline, standardize market order, and improve the overall image and reputation of the industry.
4. Policy Support Recommendations:
   • Increase policy support and financial subsidies for trenchless rehabilitation technologies to promote technology promotion and application.
   • Incorporate pipeline rehabilitation into urban infrastructure renewal and transformation plans and increase capital investment.
   • Encourage technological innovation and progress and support related scientific research projects and demonstration projects.
   • Strengthen international cooperation and promote Chinese technology and equipment to "go global."

In summary, stainless steel sliplining, as an advanced trenchless pipeline rehabilitation technology, has broad application prospects and development potential. With the development of materials science, manufacturing technology, and digital technology, this technology will continue to innovate and improve, providing strong support for the safe operation and sustainable development of urban infrastructure in China.

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