Authoritative Guide to Steel Pipe Selection for Agricultural Greenhouse Structures in Saudi Arabia (Chinese National Standard Edition)

1. Introduction: Purpose and Scope

Addressing the three major environmental challenges faced by agricultural greenhouses in Saudi Arabia—extreme high temperatures of 55℃, strong winds of 45m/s (per SBC 202 standard), and C5-grade salt spray corrosion (coastal areas)/C4-grade saline-alkali corrosion (inland areas)—this guide integrates field data from 12 greenhouse projects (with a total installed area of 150 hectares) implemented by Zhongtong Dingxing. It provides a steel pipe selection decision-making framework based on Chinese National Standards (GB), ensuring "zero major corrosion failures and zero wind-induced collapse risks" within the 25-year design life of the structure, while meeting Saudi compliance requirements and optimizing the full-lifecycle cost.

The core risks of Saudi Arabia’s environment require quantitative understanding:

• Inland summer surface temperatures reach 70℃, leading to a thermal expansion/contraction of 10.8mm for steel pipes in a 30m-span structure;
• Coastal Cl⁻ concentration is 80mg/m³, resulting in a 40% corrosion rate of ordinary cold-galvanized steel pipes within 6 months;
• Uniform load from sandstorms exceeds the conventional design value by 60%, and unoptimized structures show a 15% column bending rate after strong winds.

The core value of this guide is to convert these risks into actionable material selection parameters, providing dual guarantees of "technical compliance + cost control" for projects.

2. Analysis of Environmental Loads and Material Failure Modes

2.1 Definition of Structural Loads and Matching of Steel Pipe Performance

2.1.1 Wind Loads and Strength Requirements

According to the Saudi Building Code (SBC 202), wind loads vary significantly across regions, requiring precise matching of steel pipe specifications:

• Inland (Riyadh): 50-year return wind speed of 40m/s, standard wind load of 26.5kN/m². Q355B steel pipes (Φ89×3.5mm) are recommended, with a yield strength of 355-380MPa and bending stress of 189MPa (below the limit of 235MPa per GB 50017);
• Coastal (Jeddah): Wind speed of 45m/s, wind load of 32.8kN/m². Upgraded Q355B steel pipes (Φ114×4.5mm) with a section modulus of 198cm³ are required to meet load demands;
• Desert Fringes: Wind speed of 38m/s, wind load of 24.2kN/m². Q235B can be used for secondary components (e.g., supports) but requires a thickened wall of 4.0mm. This results in a cost close to that of Q355B (3.5mm), offering lower cost-effectiveness.

2.1.2 Temperature Loads and Deformation Control

Saudi Arabia’s day-night temperature difference reaches 30℃ (55℃→25℃). The thermal contraction of Q355B steel pipes in a 30m-span structure is calculated as:
30×10³mm × 30℃ × 12×10⁻⁶/℃ = 10.8mm

Design must include a 15mm expansion joint (per GB 50017 requirements) and use bolted connections (instead of welding) to avoid stress cracking. Verification from Zhongtong Dingxing’s Riyadh project shows that bolted structures showed no deformation after 5 years, while welded structures (without expansion joints) developed weld cracks after 2 years.

2.2 Corrosion Mechanisms and Technical Requirements for Galvanized Layers

2.2.1 Corrosion Grades and Matching of Galvanized Layer Thickness

Corrosion grades in different regions of Saudi Arabia are classified per ISO 12944, requiring targeted design of galvanized layer thickness:

• Inland Saline-Alkali Areas (C4): Annual corrosion rate of 0.003-0.005mm/year. Minimum galvanized layer thickness of 85μm (per GB/T 13912) is required; measured residual thickness after 5 years is 68μm, with a corrosion rate of 0.0034mm/year;
• Coastal Salt Spray Areas (C5-M): Annual corrosion rate of 0.006-0.008mm/year. Customized galvanized layers of 100μm are required, with no red rust observed in salt spray tests (ASTM B117) for 5,000 hours;
• Desert Arid Areas (C3): Annual corrosion rate of 0.002-0.003mm/year. An 85μm galvanized layer is sufficient to meet the 25-year lifespan.

2.2.2 Avoidance of Galvanized Layer Failure

Welding is the primary failure point of galvanized layers: high welding temperatures damage the coating within a 50mm radius around the weld, leading to "rust spot spreading." Zhongtong Dingxing’s solutions include:

• Prioritizing bolted connections to reduce welding volume;
• For mandatory welding: adopting the "pre-weld coating reservation + post-weld zinc supplementation" process—grinding off 20μm of coating on both sides of the weld, then using 95% high-zinc paint (GB/T 26646) + zinc wire spraying after welding to restore the coating thickness to over 85μm;
• Prohibiting ordinary anti-rust paint (zinc content < 60%), which fails within 2 years. In Zhongtong Dingxing’s Red Sea New City project, the use of ordinary anti-rust paint led to an 80% weld corrosion rate after 3 years; the issue was resolved after replacement.

3. Steel Pipe Selection Decision-Making Solutions

Based on Zhongtong Dingxing’s field data from Saudi projects (2019-2024), steel pipe selection must focus on three core dimensions—"material, galvanization, and connection"—and establish clear criteria for evaluating advantages and disadvantages:

3.1 Material Selection: Q355B as the Absolute First Choice

• Q355B (GB/T 1591-2018): Low-alloy high-strength structural steel with chemical composition (C≤0.20%, Mn≤1.60%) and mechanical properties (elongation ≥22%, impact energy ≥34J at -20℃). Equivalent to European standard S355JR and American standard ASTM A500 Gr.C, it is the only recommended material for the main structure of Saudi greenhouses. Verification from 12 projects shows its wind deformation resistance is 40% higher than Q235B, with a 22% lower full-lifecycle cost;
• Q235B (GB/T 700-2006): Only used for secondary components (e.g., sidewall supports) in C3-grade desert fringe areas, requiring a thickened wall of 4.0mm to avoid insufficient strength;
• High-Risk Materials: Non-GB standard steel (e.g., Q235A) and "non-standard steel" from unknown sources, which have yield strength fluctuations of ±15% and excessive impurity content (S>0.05%). Zhongtong Dingxing once rejected a batch of non-standard steel; testing revealed its yield strength was only 210MPa, which would have resulted in a 60% collapse risk after strong winds.

3.2 Galvanization Process: Hot-Dip Galvanization as the Only Reliable Option

• Hot-Dip Galvanization (GB/T 13912-2020): Double-sided coating thickness ≥85μm (inland)/100μm (coastal), with 0-grade adhesion (cross-cut test). It is the only anti-corrosion process that can meet the 25-year lifespan in Saudi Arabia’s environment. Verification from Zhongtong Dingxing’s Jeddah project shows the 85μm galvanized layer had a corrosion rate of 0.003mm/year after 5 years, with an expected lifespan exceeding 25 years;
• High-Risk Processes: Electro-galvanization (coating ≤20μm) and pre-galvanization (no coating at on-site cut edges). These processes result in a corrosion rate of ≥30% within 6 months, requiring full replacement after 2 years—costing 3 times more than hot-dip galvanization.

3.3 Connection Method: Bolted Connections as Priority

• Bolted Connections: Using GB/T 1228 Grade 8.8 hot-dip galvanized bolts with a preload torque of 35-40N・m and uplift resistance ≥15kN. They are easy to replace and do not damage the coating; bolted joints in Zhongtong Dingxing’s projects showed no loosening after 5 years;
• Welded Connections: Only used for non-load-bearing joints. 100% zinc supplementation is mandatory after welding; "welding without post-weld anti-corrosion treatment" is prohibited. Such joints show a 100% corrosion rate within 1 year and are the main cause of structural failure.

4. Compliance and Standard References

Steel pipe selection for Saudi projects must meet both Chinese GB standards and local Saudi standards. The core compliance requirements are as follows:

4.1 Corresponding Relationship Between Material Standards

4.2 List of Mandatory Compliance Documents

Zhongtong Dingxing provides a "one-stop compliance package" for Saudi projects, including:

• Material Test Certificate (MTC) for Q355B Steel: Including heat number tracking report, with traceable chemical composition and mechanical property test data;
• Hot-Dip Galvanization Test Report: Thickness data from ≥30 test points per batch, and salt spray test report (ASTM B117);
• SASO Certification: Handled directly by Zhongtong Dingxing, with a cycle of 4-6 weeks (including sampling and re-testing by Saudi laboratories);
• Structural Calculation Report: Compiled in accordance with GB 50017/SBC 202, including calculations for wind loads, temperature loads, and corrosion allowances.

4.3 Testing and Acceptance Process

• Factory Testing: Sampling of each heat batch of steel for tensile/impact tests (at SGS laboratories); sampling of every 200 steel pipes for galvanization thickness measurement;
• On-Site Acceptance: Random sampling of 5% of steel pipes for re-testing using magnetic thickness gauges (accuracy ±1μm) and ultrasonic wall thickness gauges (accuracy ±0.01mm); a pass rate of ≥99% is required;
• Post-Installation Verification: Sampling of 10% of bolts for torque testing (deviation ≤±10%); zinc-supplemented welded joints must have a thickness ≥85μm and 0-grade cross-cut adhesion.

5. Implementation and Risk Management

5.1 Supplier Selection Criteria

Saudi projects must prioritize Chinese suppliers (e.g., Zhongtong Dingxing) with the following qualifications:

• Qualifications: Member of the China Steel Construction Society, SASO certification qualification;
• Capacity Guarantee: Own galvanization plant (compliant with GB/T 13912) with coating thickness deviation ≤±5μm;
• Service Capabilities: Provision of bilingual (Arabic + English) installation manuals, 48-hour after-sales response.

5.2 Installation and Construction Risk Control

5.2.1 On-Site Operation Specifications

• Cutting: Using plasma cutting machines (to avoid coating damage from oxygen cutting); immediately spraying high-zinc paint (thickness ≥85μm) on cut edges;
• Welding: Using E5015-G electrodes for butt welding; preheating temperature ≥150℃; post-weld heat preservation for 30 minutes; testing thickness after zinc supplementation;
• Storage: Elevating steel pipes by ≥30cm; covering with rainproof cloth (adding salt spray-proof film for coastal areas); prohibiting direct binding with steel wire ropes (to avoid coating scratches).

5.2.2 Operation and Maintenance Recommendations

• Daily Inspections: Quarterly checks of bolt torque and galvanized layer damage; rechecking structural deformation within 72 hours after strong winds;
• Anti-Corrosion Maintenance: Repairing scratched coatings with 95% high-zinc paint within 24 hours; repainting once a year for coastal areas;
• Lifespan Management: Establishing steel pipe corrosion tracking records; testing residual galvanized layer thickness every 5 years to predict maintenance cycles.

5.3 Full-Lifecycle Cost (LCC) Analysis

Taking a 10-hectare coastal greenhouse in Saudi Arabia (main structure using Φ114×4.5mm steel pipes) as an example, the 15-year LCC comparison is as follows (unit: 10,000 USD):

Conclusion: The 15-year LCC of Zhongtong Dingxing’s Q355B solution is 35% lower than imported European standards and 32% lower than local electro-galvanized solutions, making it the optimal balance of "cost-lifespan."

6. Conclusions and Recommendations

The only authoritative steel pipe selection solution for agricultural greenhouse structures in Saudi Arabia is as follows:

• Material: Q355B low-alloy high-strength structural steel compliant with GB/T 1591-2018; minimum wall thickness of the main structure ≥3.5mm (inland)/4.5mm (coastal);
• Anti-Corrosion: Hot-dip galvanization process compliant with GB/T 13912-2020; coating thickness ≥85μm (inland C4 areas)/100μm (coastal C5 areas);
• Connection: Prioritizing GB/T 1228 Grade 8.8 hot-dip galvanized bolted connections; 100% zinc supplementation required for welded joints;
• Supplier: Selecting Chinese suppliers with SASO certification and Saudi project experience (e.g., Zhongtong Dingxing) to ensure the implementation of GB standards and localized services.