DIN 30670은 독일에서 가스 및 수도 공급을 위한 매립된 철도 파이프라인에 적용되는 폴리에틸렌 부식 방지 코팅에 관한 핵심 기술 표준입니다. 이 표준에 따른 3PE 코팅의 벗겨짐 강도 시험은 코팅과 기재물 사이의 접착성뿐만 아니라 이중층 접착성도 검증하는 데 중점을 두고 있습니다. 모든 시험 작업은 체계적인 오류 및 인적 오차를 제거하기 위해 표준 규정을 엄격히 준수해야 합니다.

표본 준비 및 조건화(준수 기준)

샘플링 및 절단 요건: 표본은 완제품의 부식 방지 파이프의 평평한 직선 부분에서 채취하여야 하며, 파이프 끝, 둘레 용접 및 결함 부위로부터 최소 50 mm 떨어져야 합니다. 코팅 띠, 구멍 또는 기계적 손상이 있는 표본은 엄격히 금지됩니다. 표본은 정밀 기계 절단으로 20mm ± 0.5mm의 표준 폭으로 준비해야 합니다. 절단 스트레스로 인해 레이어 간에 사전 탈기(pre-delamination)가 발생하지 않도록 부스러기 없는 열처리된 절단이 이루어져야 합니다. 25 ± 5 mm 크기의 미리 벗겨진 막대가 준비되어야 합니다. 이 때 표적 시험 인터페이스(FBE/강철 기판, 접착제/FBE, PE/접착제)를 손상시키지 않고 코팅 본체 또는 강철 파이프 기본 재료를 분리해야 합니다.

표본 조절 사양: 주변 온도 시험을 위해 표본은 최소 16시간 동안 23 °C ± 2 °C 및 50% ± 5% 상대 습도인 표준 환경에서 조절되어야 합니다. 상승된 온도 껍질 시험을 위해 코팅이 완전한 열 균형 상태에 도달하도록 보장하기 위해 표준 지정된 온도(예: 50 °C, 80 °C)에서 최소 45분 동안 일정한 온도 절연이 수행되어야 합니다. 테스트는 대상 온도에 도달할 때까지 시작하지 마십시오.

표본 보관 제한 사항: 준비된 표본은 빛이 들어오지 않는 안정적인 온도 환경에서 보관해야 합니다. 코팅 접착 특성의 돌연변이를 방지하기 위해 기름이나 용제에 접촉하거나 직접 고온에 노출하는 것은 엄격히 금지됩니다.

시험 장비 및 파라미터 제어(정확도 핵심 요소)

장비 교정 및 정밀도: 인장 시험기는 ISO 7500-1의 Class 1 정확도 요건을 충족해야 하며, 법적으로 교정된 힘 측정 시스템을 갖추어야 합니다. 유효 기간 내에. 폴리에틸렌 표면 코팅이 부서지지 않도록 되도록 중등도의 클램핑 힘으로 특수 비금속 슬립 방지 클램프를 사용해야 합니다.

일정한 파라미터 요구 사항: DIN 30670은 90° 껍질 벗기기 모드를 규정하며, 껍질 벗기기 각도 편차는 ≤ ±2°여야 합니다. 각도 편차는 데이터 변형을 초래하기 때문입니다. 껍질 제거 속도는 ±5 mm/min의 정확도로 100 mm/min으로 엄격하게 제어되어야 하며, 시험 중에는 시동이나 속도 변화 없이 일정한 속도로 유지되어야 합니다. 데이터 수집 주파수는 부하 변위 곡선을 완벽하게 기록하기 위해 10 Hz 이상이어야 합니다.

온도 제어 장비 요구 사항: 고온 시험용 온도 조절기는 온도 제어 정확도가 ±1 °C 이하이고, 지역적 과열이 발생하지 않아야 합니다. 또는 온도 변동. 시험 중 시료 조정을 위해 온도 조절기를 열어 사용하는 것은 시험 결과에 영향을 미치는 갑작스러운 온도 변화를 방지하기 위해 금지됩니다.

시험 운영 및 실패 결정(유효성 확인 키)

표준 클램핑 작동: 표본은 껍질 벗기기 힘의 동축적 정렬을 보장하고, 휨이나 변형이 없도록 클램핑하여 직선적인 껍질 벗기기 경로를 확보해야 합니다. 껍질 길이의 처음 50mm와 마지막 20mm는 불안정한 응력 구간으로 간주되며, 이 구간의 데이터는 버려야 합니다. 연속적이고 안정적인 중간 껍질 벗기기 구간의 데이터만 수집해야 합니다.

결함 모드 결정: DIN 30670에서는 접합부 결함이 유효한 결함 모드라고 정의합니다. 시험 결과는 무효화되며, 코팅의 조립 결함, 시편 절단 손상으로 인한 조기 벗겨짐, 클램프 미끄러짐 또는 기판 변형이 시험 중 발생하면 재시험이 필요합니다. 고장 인터페이스의 종류는 정확히 기록되어야 하며, 서로 다른 인터페이스의 껍질 벗김 성능은 별도의 그룹에서 시험 및 문서화되어야 합니다.

비동시적 시료 관리: 각 시험 그룹에는 최소 5개의 비동시적 시료가 포함되어야 합니다. 분산 계수가 > 15%인 이상한 데이터는 제외되며, 남은 유효 시료의 평균값을 최종 결과로 삼습니다.

데이터 계산 및 기록 추적성(규정 준수 보장)

데이터 계산 기준: 페일 강도는 실제 시편 폭을 기준으로 한 단위 폭당 하중으로 계산된 N/mm로 보고됩니다. 규정 준수는 DIN 30670의 온도 규정 제한치에 따라 결정됩니다. 단일 시편의 측정값은 표준 하한치의 80%보다 낮아서는 안 되며, 그룹 평균은 표준 인덱스 요건을 충족해야 합니다.

추적 가능 기록 요건: 시험 보고서는 DIN 30670 표준 개정판, 시편 번호, 장비 교정 번호, 주변 온도 및 기타 사항을 완전히 명시해야 합니다. 습도, 절연 시간, 벗겨짐 각도/속도, 고장 모드, 원시 부하 데이터 및 곡선. 시험 시료는 재검사 및 추적성을 위해 보고서 발간까지 보관해야 합니다.

DIN 30670은 독일에서 가스 및 수도 공급을 위한 매립된 철도 파이프라인에 적용되는 폴리에틸렌 부식 방지 코팅에 관한 핵심 기술 표준입니다. 이 표준에 따른 3PE 코팅의 벗겨짐 강도 시험은 코팅과 기재물 사이의 접착성뿐만 아니라 이중층 접착성도 검증하는 데 중점을 두고 있습니다. 모든 시험 작업은 체계적인 오류 및 인적 오차를 제거하기 위해 표준 규정을 엄격히 준수해야 합니다.

표본 준비 및 조건화(준수 기준)

샘플링 및 절단 요건: 표본은 완제품의 부식 방지 파이프의 평평한 직선 부분에서 채취하여야 하며, 파이프 끝, 둘레 용접 및 결함 부위로부터 최소 50 mm 떨어져야 합니다. 코팅 띠, 구멍 또는 기계적 손상이 있는 표본은 엄격히 금지됩니다. 표본은 정밀 기계 절단으로 20mm ± 0.5mm의 표준 폭으로 준비해야 합니다. 절단 스트레스로 인해 레이어 간에 사전 탈기(pre-delamination)가 발생하지 않도록 부스러기 없는 열처리된 절단이 이루어져야 합니다. 25 ± 5 mm 크기의 미리 벗겨진 막대가 준비되어야 합니다. 이 때 표적 시험 인터페이스(FBE/강철 기판, 접착제/FBE, PE/접착제)를 손상시키지 않고 코팅 본체 또는 강철 파이프 기본 재료를 분리해야 합니다.

표본 조절 사양: 주변 온도 시험을 위해 표본은 최소 16시간 동안 23 °C ± 2 °C 및 50% ± 5% 상대 습도인 표준 환경에서 조절되어야 합니다. 상승된 온도 껍질 시험을 위해 코팅이 완전한 열 균형 상태에 도달하도록 보장하기 위해 표준 지정된 온도(예: 50 °C, 80 °C)에서 최소 45분 동안 일정한 온도 절연이 수행되어야 합니다. 테스트는 대상 온도에 도달할 때까지 시작하지 마십시오.

표본 보관 제한 사항: 준비된 표본은 빛이 들어오지 않는 안정적인 온도 환경에서 보관해야 합니다. 코팅 접착 특성의 돌연변이를 방지하기 위해 기름이나 용제에 접촉하거나 직접 고온에 노출하는 것은 엄격히 금지됩니다.

시험 장비 및 파라미터 제어(정확도 핵심 요소)

장비 교정 및 정밀도: 인장 시험기는 ISO 7500-1의 Class 1 정확도 요건을 충족해야 하며, 법적으로 교정된 힘 측정 시스템을 갖추어야 합니다. 유효 기간 내에. 폴리에틸렌 표면 코팅이 부서지지 않도록 되도록 중등도의 클램핑 힘으로 특수 비금속 슬립 방지 클램프를 사용해야 합니다.

일정한 파라미터 요구 사항: DIN 30670은 90° 껍질 벗기기 모드를 규정하며, 껍질 벗기기 각도 편차는 ≤ ±2°여야 합니다. 각도 편차는 데이터 변형을 초래하기 때문입니다. 껍질 제거 속도는 ±5 mm/min의 정확도로 100 mm/min으로 엄격하게 제어되어야 하며, 시험 중에는 시동이나 속도 변화 없이 일정한 속도로 유지되어야 합니다. 데이터 수집 주파수는 부하 변위 곡선을 완벽하게 기록하기 위해 10 Hz 이상이어야 합니다.

온도 제어 장비 요구 사항: 고온 시험용 온도 조절기는 온도 제어 정확도가 ±1 °C 이하이고, 지역적 과열이 발생하지 않아야 합니다. 또는 온도 변동. 시험 중 시료 조정을 위해 온도 조절기를 열어 사용하는 것은 시험 결과에 영향을 미치는 갑작스러운 온도 변화를 방지하기 위해 금지됩니다.

시험 운영 및 실패 결정(유효성 확인 키)

표준 클램핑 작동: 표본은 껍질 벗기기 힘의 동축적 정렬을 보장하고, 휨이나 변형이 없도록 클램핑하여 직선적인 껍질 벗기기 경로를 확보해야 합니다. 껍질 길이의 처음 50mm와 마지막 20mm는 불안정한 응력 구간으로 간주되며, 이 구간의 데이터는 버려야 합니다. 연속적이고 안정적인 중간 껍질 벗기기 구간의 데이터만 수집해야 합니다.

결함 모드 결정: DIN 30670에서는 접합부 결함이 유효한 결함 모드라고 정의합니다. 시험 결과는 무효화되며, 코팅의 조립 결함, 시편 절단 손상으로 인한 조기 벗겨짐, 클램프 미끄러짐 또는 기판 변형이 시험 중 발생하면 재시험이 필요합니다. 고장 인터페이스의 종류는 정확히 기록되어야 하며, 서로 다른 인터페이스의 껍질 벗김 성능은 별도의 그룹에서 시험 및 문서화되어야 합니다.

비동시적 시료 관리: 각 시험 그룹에는 최소 5개의 비동시적 시료가 포함되어야 합니다. 분산 계수가 > 15%인 이상한 데이터는 제외되며, 남은 유효 시료의 평균값을 최종 결과로 삼습니다.

데이터 계산 및 기록 추적성(규정 준수 보장)

데이터 계산 기준: 페일 강도는 실제 시편 폭을 기준으로 한 단위 폭당 하중으로 계산된 N/mm로 보고됩니다. 규정 준수는 DIN 30670의 온도 규정 제한치에 따라 결정됩니다. 단일 시편의 측정값은 표준 하한치의 80%보다 낮아서는 안 되며, 그룹 평균은 표준 인덱스 요건을 충족해야 합니다.

추적 가능 기록 요건: 시험 보고서는 DIN 30670 표준 개정판, 시편 번호, 장비 교정 번호, 주변 온도 및 기타 사항을 완전히 명시해야 합니다. 습도, 절연 시간, 벗겨짐 각도/속도, 고장 모드, 원시 부하 데이터 및 곡선. 시험 시료는 재검사 및 추적성을 위해 보고서 발간까지 보관해야 합니다.

1. Core Classification and Technical Characteristics of FBE Coating Thickness

FBE coatings are categorized into three types based on thickness: Single-Layer Basic Type, Single-Layer Reinforced Type, and Dual-Layer Composite Type, with their performance increasing in a stepped manner as thickness increases:

2. Precise Matching of Application Scenarios by Thickness

1. Single-Layer Basic Type (300-400 μm): Conventional Corrosion Environments

• Typical Scenarios:
  • Municipal water transmission pipelines (DN ≤ 250 mm, soil resistivity ≥ 100 Ω·m)
  • Underground coal mine gas extraction pipes (pressure ≤ 1.6 MPa)
  • Thermal power plant circulating water pipelines (water temperature ≤ 60℃)
• Case Reference: The gathering and transportation pipeline network of Tarim Oilfield adopts ASTM A53 Gr.B steel pipes with 350 μm FBE coating, achieving a 98.7% coating integrity rate after 5 years.

2. Single-Layer Reinforced Type (400-500 μm): Moderately Severe Environments

• Typical Scenarios:
  • Acid-alkali waste liquid transmission in chemical industrial parks (pH 3-11)
  • Buried gas pipelines in coastal areas (soil salt content ≤ 3%)
  • Trenchless crossing pipelines under highways (anti-rolling requirements)
• Suitable Pipe Diameters: DN 250-DN 800. According to SY/T 0315, coating thickness increases with pipe diameter (e.g., ≥ 450 μm for DN 800).

3. Dual-Layer Composite Type (≥ 620 μm): Extreme Service Environments

• Typical Scenarios:
  • Submarine oil transmission pipelines (water depth ≤ 50 m, seawater immersion resistance)
  • High-temperature steam pipelines (temperature ≤ 120℃, thermal aging resistance)
  • Buried pipelines in rocky areas (gravel scratch resistance)
• Standard Requirement: Complies with the “Extra Reinforced Class” specification in DIN 30671, with top layer thickness ≥ 400 μm.

4. FBE Base Layer in Composite Structures (120-200 μm)

• Application Form: Serves as the bonding base layer for 3PE/3PP coatings
• Scenario Adaptation: Long-distance oil and gas transmission pipelines (DN ≥ 500 mm)
• Thickness Specification: GB/T 23257 requires the FBE base layer to be ≥ 120 μm for pipes with DN ≤ 100 mm, and ≥ 180 μm for pipes with DN ≥ 800 mm.

3. Core Domestic and International Standards & Thickness Regulations

1. Chinese Standards

2. International Standards

• DIN 30671 (Germany):
  • Normal Class: 300-400 μm (buried in soil)
  • Reinforced Class: ≥ 500 μm (underwater or rocky areas)
• AWWA C210 (USA):
  • Drinking water pipelines: Single layer ≥ 300 μm, no heavy metal leaching
• ISO 21809-1 (International):
  • Dual-Layer FBE: Base layer 120-150 μm, top layer ≥ 500 μm

4. Key Considerations for Selection

1. Corrosion Grade Matching:
   • Mild corrosion (soil resistivity > 500 Ω·m): Select 300-400 μm single-layer coating
   • Severe corrosion (salt marshes/chemical industrial zones): Mandatory use of ≥ 620 μm dual-layer coating
2. Pipe Diameter Correlation Principle:
   • DN ≤ 100 mm: Minimum thickness 300 μm (to avoid brittleness and cracking caused by excessive coating thickness)
   • DN ≥ 800 mm: Reinforced class ≥ 450 μm (to resist greater external pressure)
3. Core Acceptance Indicators:
   • Thickness Uniformity: Deviation ≤ ±50 μm for the same pipe section (per SY/T 0315)
   • Cathodic Disbondment: Immersion at 70℃ for 30 days, disbondment width ≤ 10 mm

The transportation and storage of Fusion-Bonded Epoxy (FBE)-coated steel pipes are critical links in ensuring their corrosion protection performance. Although FBE coatings exhibit excellent corrosion resistance, they are relatively brittle with poor impact and scratch resistance, and are sensitive to ambient temperature, humidity, and mechanical forces. Therefore, standardized transportation and storage management is essential to prevent coating damage, aging, or structural damage to the pipes, thereby ensuring the effectiveness of subsequent construction and long-term operation. Below are the specific operational specifications:

1. Preparation Before Transportation

Before transportation, coating quality verification 그리고 protective pre-treatment must be completed to minimize the risk of damage during transportation:

1.1 Coating Quality Re-inspection

• In accordance with GB/T 39636-2020 Technical Specification for Fusion-Bonded Epoxy Powder External Coatings on Steel Pipes, re-inspect the coating’s appearance (no pinholes, bubbles, or peeling), thickness (single layer ≥ 300μm, double layer ≥ 600μm), and adhesion strength (≥ 10MPa). Non-conforming products must be repaired before transportation.
• Conduct a comprehensive inspection of coating integrity using a spark tester (15kV voltage) to ensure no leakage points (inspection speed ≤ 0.3m/s).

1.2 Protection of Pipe Ends

• Fit plastic protective caps (HDPE material, thickness ≥ 3mm) on both ends of the pipes (beveled or flat ends) to prevent foreign objects from entering the pipe interior and avoid collision damage to the coatings at the ends.
• For flanged pipes, cover the flange sealing surfaces with anti-rust film + rigid protective covers to prevent scratches or rust on the sealing surfaces.

1.3 Selection of Packaging Methods

Choose appropriate packaging based on the pipe specifications (length, diameter), with the core goal of preventing friction and collision between pipes:

2. Transportation Process Control

During transportation, focus on preventing mechanical impact, friction scratches, and environmental erosion. The specific requirements are as follows:

2.1 Loading and Unloading Specifications

• 사용 specialized lifting equipment exclusively: Prioritize hooks and slings (width ≥ 100mm) with soft liners (rubber or nylon). Direct bundling of pipes with steel wire ropes is prohibited (to avoid indentation damage to the coating).
• Control the loading/unloading speed at ≤ 0.5m/s. Throwing or impacting is prohibited. Pipes must be kept horizontal when lifted to prevent coating scratches caused by tilting.

2.2 Transportation Vehicles and Fixation

• 사용 flatbed trucks or dedicated tank trucks. The truck bed must be paved with non-slip rubber sheets or wooden pads (thickness ≥ 10mm) to prevent pipe sliding during transportation.
• Pipe fixation methods:
  • For bundled short pipes: Secure them with steel strips + soft pads (a second round of fixation). Place non-woven fabrics between the steel strips and the coating to avoid direct metal contact.
  • For long pipes in frames: Fix the frames to the truck bed with bolts, and secure the pipes inside the frames with wedges (wooden, with soft liners attached) to prevent displacement due to jolting.

2.3 Environmental Protection Measures

• Transportation in rainy weather: Pipes must be covered with rainproof tarpaulins (PVC material, thickness ≥ 0.3mm). Ventilation holes (1 hole every 5m, diameter ≥ 50mm) must be reserved on the tarpaulins to prevent condensation accumulation in the truck bed, which could dampen the coating.
• Transportation in high temperatures (ambient temperature > 35℃): Cover the top of the truck bed with sunshade nets to avoid prolonged exposure of the FBE coating to sunlight (which accelerates coating aging).
• Transportation in low temperatures (ambient temperature < 0℃): For long-distance transportation (> 24h), provide preheating protection for the coating surface (cover with thermal insulation cotton to prevent coating embrittlement due to low temperatures).

2.4 Transportation Routes and Speed

• Prioritize smooth highways and avoid bumpy roads (e.g., unpaved roads, potholed sections). Maintain a driving speed ≤ 60km/h (≤ 80km/h on highways). Decelerate gently when turning or braking to prevent pipe impact caused by sudden stops.

3. Storage Management Specifications

The storage of FBE-coated steel pipes must meet the requirements of moisture prevention, pressure prevention, and corrosion prevention. Strictly follow the following standards for storage sites and stacking methods:

3.1 Requirements for Storage Sites

• The site must have hardened ground (concrete or asphalt, flatness tolerance ≤ 5mm) with a drainage slope ≥ 3‰ to prevent water accumulation from soaking the pipes.
• Keep away from corrosive environments: Prohibit placement near chemical industrial zones, salt spray areas, or sewage ditches. Set up guardrails around the site to prevent unauthorized mechanical access.
• Environmental control for the site: The storage temperature should be -5℃ ~ 35℃, with relative humidity ≤ 85%. For long-term storage (> 3 months), build sunshade sheds (top height ≥ 4m) to avoid direct sunlight and rain erosion.

3.2 Stacking Methods and Load Control

• Bottom support: Use wooden or concrete support blocks (height ≥ 200mm, spacing between supports ≤ 3m). Attach soft liners (rubber, thickness ≥ 10mm) to the top of the support blocks. Direct placement of pipes on the ground is prohibited.
• Stacking height:
  • For pipes with diameter ≤ 500mm: Maximum stacking height ≤ 5 layers, with rubber pads (thickness ≥ 5mm) placed between each layer.
  • For pipes with diameter > 500mm: Maximum stacking height ≤ 3 layers. Mark the bottom-layer pipes separately to prevent long-term compression deformation.
• Stacking spacing: Pipes of different specifications and batches must be stored in separate zones with a spacing ≥ 1m between zones. Install identification signs (indicating specifications, production date, and coating type) for easy management.

3.3 Maintenance for Long-Term Storage

• Regular inspections: Daily check the coating appearance (for scratches or bubbles); weekly inspect whether the support blocks are deformed or the ground is waterlogged; monthly conduct random inspections of coating integrity using a spark tester (sampling ratio ≥ 5%).
• Environmental regulation: Strengthen ventilation during the rainy season (open the side curtains of the sunshade shed). In winter, if the site temperature < -10℃, provide intermittent preheating for the pipes (use a hot air blower to blow the coating surface, controlling the temperature at 10℃ ~ 15℃ to prevent coating embrittlement).
• End protection: If the plastic protective caps fall off, replace them immediately to prevent dust and moisture from entering the pipe interior and causing internal rust.

4. Common Issues and Emergency Handling

4.1 Coating Scratches During Transportation

• For minor scratches (scratch area ≤ 30mm²): Upon arrival at the destination, immediately repair using a special FBE repair agent (two-component liquid epoxy). Follow the process: grinding → cleaning → application → curing. Conduct a spark test after repair.
• For moderate scratches (scratch area > 30mm²): Mark the location, prohibit use, and contact the manufacturer to send professionals for on-site repair or return the pipes to the factory for handling.

4.2 Coating Blistering During Storage

• Cause: Mostly due to site humidity and water ingress between the coating and the substrate.
• Handling: Cut open the blistered area, remove moisture and rust, re-blast the surface (to Sa2.5 standard), apply FBE powder, and test the adhesion strength (≥ 10MPa) after curing.

4.3 Pipe Deformation

• For slight bending deformation (deformation ≤ L/1000, where L is the pipe length): Straighten slowly using a dedicated straightening machine, and re-inspect the coating integrity after straightening.
• For severe deformation (deformation > L/1000): Classify as scrapped and prohibit use.

FBE (Fusion Bonded Epoxy) anti-corrosion steel pipes use steel pipes as the matrix, and the epoxy powder is melted and cured on the surface of the steel pipes through high-temperature spraying to form an anti-corrosion layer. To improve the service life of FBE anti-corrosion steel pipes, efforts can be made in multiple links such as production and manufacturing, transportation and storage, installation and use, and later maintenance:

Production and Manufacturing Link

• Optimize Steel Pipe Pretreatment: The cleanliness and roughness of the steel pipe surface directly affect the adhesion of the FBE coating. Before coating, shot blasting or sandblasting is used to thoroughly remove impurities such as rust, oil stains, and oxide scales on the steel pipe surface, so that the steel pipe surface reaches Sa2.5 level (near-white level), and the roughness is controlled at 40 – 100μm. Appropriate roughness can increase the contact area between the coating and the steel pipe, enhance adhesion, reduce the risk of coating peeling, and prolong the service life.
• Strictly Control the Coating Process: Precisely control the spraying temperature, thickness, and curing time of the epoxy powder. Generally, the spraying temperature is 230 – 250℃, the coating thickness is controlled at 300 – 500μm according to the requirements of the use environment, and the curing time needs to ensure that the powder is completely melted and cross-linked and cured. A stable coating process can ensure that the coating is uniform, dense, and free of defects such as pinholes and bubbles, effectively blocking the intrusion of corrosive media.
• Select High-Quality Raw Materials: Select reliable-quality epoxy powder to ensure that it has good chemical corrosion resistance, water resistance, weather resistance, and mechanical properties. High-quality epoxy powder can maintain stable anti-corrosion performance for a long time in different environments. At the same time, the quality of the steel pipe itself is also crucial. Select steel pipes that meet relevant standards, have uniform wall thickness, and excellent material quality to reduce corrosion problems caused by defects of the steel pipes themselves.

Transportation and Storage Link

• Strengthen Protective Packaging: During transportation, use appropriate packaging materials for FBE anti-corrosion steel pipes, such as wrapping with plastic film or protective sleeves specially for anti-corrosion pipes, to prevent damage to the coating due to collision and friction between steel pipes. For long-distance transportation, soft pads should be laid at the bottom of the carriage, and the steel pipes should be fixed to avoid coating damage caused by transportation bumps.
• Reasonably Plan Storage: The storage site should be a dry and well-ventilated place to avoid the steel pipes being in a humid environment for a long time. The steel pipes should be stored elevated, keeping a certain distance from the ground to prevent the coating from being eroded by ground moisture. At the same time, direct sunlight should be avoided to prevent the coating from aging due to ultraviolet radiation and shortening the service life.

Installation and Use Link

• Standardize Installation Operations: During the installation process, strictly follow the operating procedures, avoid pulling and bending the steel pipes with force, and prevent the coating from cracking or peeling due to excessive force. Use appropriate connection methods. For example, when welding, protective measures should be taken to prevent welding spatter from damaging the coating. For coating damage caused during the installation process, it should be repaired in a timely manner to ensure the integrity of the anti-corrosion layer.
• Control the Use Environment: Try to avoid using FBE anti-corrosion steel pipes in harsh environments such as extreme temperatures, high humidity, and strong acids and alkalis. If unavoidable, additional protective measures can be taken, such as adding an insulating layer and a protective sleeve outside the pipeline, to reduce the erosion of the environment on the coating. At the same time, parameters such as the temperature, 酸碱度 (acidity and alkalinity), and flow rate of the conveying medium should be controlled to reduce the corrosion effect of the medium on the steel pipes and the coating.

Later Maintenance Link

• Regular Detection and Evaluation: Establish a regular detection system, and use technical means such as ultrasonic detection and leak point detection to check the integrity, adhesion of the FBE coating, and the corrosion of the steel pipes. Through regular detection, potential problems can be found in a timely manner, and corresponding repair measures can be taken to prevent the problems from expanding.
• Timely Repair the Coating: Once problems such as coating damage and aging are found, the coating should be repaired in a timely manner. According to the degree of coating damage, select an appropriate repair method. For example, for small-area damage, manual brushing or spraying of epoxy repair paint can be used; for large-area damage, re-FBE coating treatment is required.

During the heat treatment process of steel pipes, various defects may occur due to improper process parameters, equipment failures, or operational errors. The following is a detailed analysis of common defects and their preventive measures:

I. Defects in the Heating Stage

1. Oxidation and Decarburization
   Defect manifestation: An oxide scale (Fe₃O₄, Fe₂O₃) forms on the surface of the steel pipe, and the loss of carbon elements leads to a decrease in surface hardness.
   Cause: Excessive air (oxidizing atmospheres such as O₂, H₂O, etc.) in the heating furnace, too high a heating temperature, or too long a holding time.
   Preventive measures:
   Use a controlled atmosphere furnace (such as N₂, Ar protective gas, or drip methanol and acetone to generate a protective atmosphere).
   Coat the surface of the workpiece with an anti-oxidation coating (such as a borax coating).
   Strictly control the heating temperature and time to avoid overheating.
2. Coarse Grain (Overheating)
   Defect manifestation: The austenite grains grow excessively, resulting in a decrease in mechanical properties (reduction in toughness and plasticity).
   Cause: The heating temperature exceeds the critical temperature by a large margin (for example, overheating occurs when the quenching heating temperature is 50~80℃ higher than the Ac3 line), or the holding time is too long.
   Preventive measures:
   Accurately set the heating temperature (according to the process specifications of the steel grade, for example, the quenching temperature of 45 steel is 840±10℃).
   Adopt stepwise heating or rapid heating technology to reduce the residence time at high temperatures.
   For overheated workpieces, they can be reprocessed through normalizing (to refine the grains).

II. Defects in the Cooling Stage

1. Quenching Cracks
   Defect manifestation: Transgranular cracks appear on the surface or inside of the workpiece, mostly occurring at the sudden change of the cross-section, sharp corners, or holes.
   Cause:
   The cooling rate is too fast (for example, when carbon steel is cooled below the Ms point, the martensitic transformation generates huge internal stress).
   The workpiece design is unreasonable (in stress concentration areas), it is not preheated, or there is machining stress before quenching.
   The cooling medium is not properly selected (for example, alloy steel is prone to cracking when quenched in brine).
   Preventive measures:
   Improve the structure of the workpiece (round off sharp corners, avoid large differences in thickness), and carry out stress-relieving annealing before quenching.
   Adopt isothermal quenching (bainitic transformation) or step quenching (first quench into a medium above the Ms point and hold it, then cool it slowly).
   Select an appropriate cooling medium (for example, 40Cr steel should be cooled in oil instead of water), and control the temperature of the quenching medium (for example, the oil temperature should not be lower than 40℃).
2. Insufficient or Uneven Hardness
   Defect manifestation: The surface or core hardness does not reach the standard, or the hardness difference in the same cross-section is >5HRC.
   Cause:
   Insufficient heating temperature (incomplete austenitization), insufficient holding time.
   Insufficient cooling rate (for example, the aging of the quenching medium and a large amount of impurities lead to a decrease in the cooling capacity).
   Surface decarburization (resulting in a lower hardness after quenching).
   Preventive measures:
   Strictly calibrate the temperature control instrument to ensure uniform heating temperature (the furnace temperature uniformity is ≤±5℃).
   Regularly replace or filter the quenching medium (for example, when the water content in the oil is >5%, the water needs to be removed).
   Control decarburization (the same as the oxidation prevention measures), and perform surface carburizing compensation if necessary.

III. Defects in the Tempering Stage

1. Tempering Brittleness
   Defect manifestation: The toughness decreases after low-temperature tempering (200~300℃) (the first type of tempering brittleness), or brittleness occurs during slow cooling after high-temperature tempering (450~650℃) (the second type of tempering brittleness).
   Cause:
   The first type: Carbides precipitate along the grain boundaries during the decomposition of martensite, which is irreversible.
   The second type: Impurity elements such as P and Sn segregate at the grain boundaries, which is reversible (reheating and rapid cooling can eliminate it).
   Preventive measures:
   Avoid tempering in the brittle temperature range, or use rapid tempering cooling (for the second type of brittleness).
   Select steel grades with low impurities, or add alloying elements such as Mo and W to inhibit grain boundary segregation.
2. Abnormal Hardness after Tempering
   Defect manifestation: The hardness after tempering is higher or lower than expected (for example, insufficient hardness after high-temperature tempering after quenching, or higher hardness after low-temperature tempering).
   Cause: Incorrect setting of the tempering temperature (for example, mistakenly setting 500℃ as 400℃), failure of the temperature control system, or insufficient holding time.
   Preventive measures:
   Calibrate the thermocouple and temperature control instrument before tempering (with an accuracy of ±1% FS), and use a dual-sensor monitoring system.
   Hold according to the process requirements (generally 1~2 hours, adjusted according to the cross-sectional thickness).

IV. Overall Defects: Deformation and Dimension Out-of-Tolerance
Defect manifestation: The steel pipe is bent, the ovality exceeds the standard (for example, the diameter tolerance is >±0.5%), and the straightness is >1mm/m.
Cause:
The self-weight of the workpiece or improper support during the heat treatment process (for example, a long steel pipe sags when heated while hanging).
There is a large temperature difference in the cross-section during cooling (for example, the cooling rates of the upper and lower surfaces are uneven during horizontal quenching).
Residual stress is not eliminated (for example, direct quenching of a cold-rolled pipe without annealing leads to stress superposition).
Preventive measures:
Use a vertical furnace to heat long steel pipes, or use supporting fixtures to keep them horizontal.
During quenching, rotate or swing the workpiece to ensure uniform cooling (for example, arrange annular nozzles during spray quenching).
Carry out annealing or normalizing before heat treatment to eliminate machining stress, and straighten the finished product (such as pressure straightening or tension straightening).

V. Preventive Management System

1. Process Standardization: Develop a “Steel Pipe Heat Treatment Process Card”, clearly defining parameters such as temperature, time, and medium (for example, the normalizing temperature of Q345B steel pipe is 880~920℃, and the holding time is 1min/mm).
2. Equipment Maintenance: Regularly calibrate the temperature control system (check once a week), clean the carbon deposits in the furnace (once a month), and check the stirring device of the quenching tank (ensure the flow rate ≥0.5m/s).
3. Process Monitoring: Use an infrared thermometer to monitor the surface temperature of the workpiece in real time, and randomly inspect the hardness (at least 3 points per pipe) and metallographic structure (for example, the martensite grade ≤3) for each batch.
4. Personnel Training: Operators must work with a certificate and master the heat treatment characteristics of different steel grades (for example, stainless steel solution treatment requires rapid water cooling to avoid the precipitation of the σ phase).

The core preventive idea for heat treatment defects of steel pipes is to precisely control the parameters of the three stages of heating, cooling, and tempering, and reduce stress concentration and organizational inhomogeneity. Through process optimization, equipment maintenance, and process monitoring, the defect rate can be effectively reduced, and the stability of the mechanical properties of steel pipes can be improved.