First, Routine Maintenance of Thick-Walled Steel Pipes.
Thick-walled steel pipes are a widely used type of steel. They directly impact economic benefits and the safety of personnel. Countries worldwide place great importance on the testing of thick-walled steel pipes, employing various non-destructive testing (NDT) methods for rigorous inspection. Therefore, appropriate maintenance and upkeep are crucial during the use of thick-walled steel pipes. Generally, a designated person should conduct daily inspections of the thick-walled steel pipes, checking for any sinking or loosening of the uprights and base plates, any slippage or loosening of the fasteners, and the completeness of all components. Proper drainage of the thick-walled steel pipe foundation is essential; a comprehensive inspection of the foundation must be conducted after rain to prevent water accumulation and subsidence. The working load on the operating level must not exceed 270 kg/m². Horizontal supports, guy ropes, etc., must not be fixed to the thick-walled steel pipes, and hanging heavy objects on them is strictly prohibited. No one is allowed to arbitrarily remove any components from the thick-walled steel pipes. Thick-walled steel pipe operations should be suspended during winds of level six or higher, heavy fog, heavy rain, or heavy snow. Work can only resume after relevant personnel have inspected and confirmed that there are no problems.
Second, the performance and economy of thick-walled steel pipes.
(1) In actual piping projects, besides those mentioned above, there are many other structural types of steel pipe fittings used to meet various working conditions, especially special working conditions. In engineering design or selection, the higher the strength grade of the steel pipe fittings, the higher the performance, but the greater the project cost, leading to waste.
(2) From an economic perspective, while meeting engineering design requirements, minimizing costs often results in a small quantity and variety of steel pipe fittings being selected, which is detrimental to the management and control of on-site construction materials and the substitution of materials required by design changes. Therefore, the selection of steel pipe fittings should be comprehensive and economical, minimizing the variety of steel pipe fittings. Furthermore, factors such as on-site construction conditions, construction level, and the procurement cycle of steel pipe fittings should also be considered in the selection of steel pipe fittings. In specific situations, the possibility of using reinforced thick-walled steel pipe joints, mitered bends, and on-site bending of small-diameter steel pipes should also be considered.
Third, Causes and Adjustments for Uneven Wall Thickness in Thick-Walled Steel Pipes:
1. Causes of Spiral Uneven Wall Thickness: Uneven wall thickness caused by factors such as misalignment of the piercing mill rolling centerline, unequal inclination angles of the two rolls, or insufficient pre-pressurization of the mandrel generally presents a spiral distribution along the entire length of the thick-walled steel pipe. Uneven wall thickness caused by premature opening of the centering roll, improper adjustment of the centering roll, and mandrel vibration during rolling also generally presents a spiral distribution along the entire length of the thick-walled steel pipe.
- Measures for Spiral Uneven Wall Thickness: Adjust the piercing mill rolling centerline to ensure equal inclination angles of the two rolls. Adjust the rolling mill according to the parameters given in the rolling schedule. For this situation, adjust the opening time of the centering roll according to the tube exit speed. During rolling, the centering roll should not open too early to prevent mandrel vibration and uneven wall thickness. The opening degree of the centering roll needs to be adjusted appropriately according to changes in the tube diameter, taking into account the amount of tube runout.
2. Causes of Linear Uneven Wall Thickness: Improper adjustment of the mandrel pre-penetration saddle height, causing the mandrel to contact the tube on one side during pre-penetration, resulting in excessively rapid temperature drop on the contact surface, leading to uneven wall thickness or even denting defects. Other causes include: Insufficient or excessive gap between rolling mill rolls; deviation of the rolling mill centerline; uneven reduction in single and double stands, causing linear symmetrical deviations in both single-stand (overly thick) and double-stand (overly thick) directions; a broken mandrel and a large difference in the inner and outer roll gaps, causing linear asymmetrical deviations in the rolling mill; and improper continuous rolling adjustments, such as steel stacking or pulling, which can cause linear uneven wall thickness.
- Measures to Address Linear Uneven Wall Thickness: Adjust the height of the mandrel pre-penetration saddle to ensure alignment between the mandrel and the tube. Measure the roll gap when changing the roll pass and rolling specifications to ensure the actual roll gap matches the rolling schedule. Adjust the rolling centerline using an optical alignment device. Correct the rolling mill centerline during the annual overhaul. 1. Replace broken stands promptly. Measure the inner and outer roll gaps of the continuous rolling mill rolls and replace any damaged sections immediately. Avoid pulling or piling steel during continuous rolling.
3. Causes of uneven wall thickness at the head and tail: Excessive skewness or curvature of the billet tip, and misalignment of the billet centering hole can easily cause uneven wall thickness at the head of thick-walled steel pipes. Excessive elongation coefficient during piercing, excessively high roll speed, and unstable rolling can also cause uneven wall thickness at the tail of the steel tube.
- Measures to address uneven wall thickness at the head and tail: Inspect the billet to prevent excessive skewness or reduction at the tip. Correct the centering hole when changing the die type or during maintenance. Use a lower piercing speed to ensure rolling stability and uniform tube wall thickness. When adjusting the roll speed, adjust the matching guide discs accordingly. Monitor the condition of the guide discs and increase the inspection of the guide disc bolts to reduce the guide disc’s movement during rolling and ensure stable steel ejection.
Post time: Dec-02-2025