Preliminary Study on the Causes of Failure in Identifying Calcium Carbide Steel Drums
Huang Rui
Calcium carbide is a highly flammable and explosive material, widely used in industrial applications. China exports over 3 million barrels of calcium carbide annually, making it a critical component of the country’s trade. However, incidents of explosions at domestic and international ports due to improper packaging have caused significant economic damage. Ensuring accurate identification of dangerous materials in calcium carbide steel drums is essential for maintaining the reputation of Chinese exports, preventing financial losses, and enhancing safety standards.
Typically, calcium carbide is packaged in open steel drums classified as Type II hazardous packages. Unlike regular open drums, these must be tightly sealed to prevent leakage. Sealing is a crucial factor during inspection and often the most common cause of failure. This paper provides an initial analysis of frequently encountered issues, aiming to encourage discussion among professionals in the field.
I. Analysis of Failure Reasons
The primary inspection of calcium carbide steel drums involves checking their appearance and airtightness.
Common appearance-related issues include rough surfaces on the drum lids and severe deformation at the top. Rough paint surfaces are usually caused by residual calcium carbide powder that becomes airborne during storage and isn't cleaned before painting. This issue is relatively easy to address. However, lid deformation is more complex and typically results from excessive nitrogen pressure during the nitrogen charging process. To prevent this, the pressure should not exceed 30 kPa, and the nitrogen filling should stop immediately once the desired pressure is reached. Operators must be trained to monitor and control the pressure accurately, rather than relying solely on experience.
Gas seal failures are more complex and can be categorized into several key areas:
(1) Air leaks through the vent hole. This is often due to low-quality sealing gaskets with poor elasticity, insufficient thickness, or uneven material distribution. Additionally, excessive force when tightening the lid after nitrogen filling can cause the gasket to tear, leading to air leakage.
(2) Leaks at the curled edge and sealing area. Three main reasons contribute to this: first, the sealing compound is not evenly mixed, resulting in gaps when the edges are crimped; second, long-term wear of the sealing machine reduces its effectiveness; third, improper handling during sealing causes uneven pressure, leading to leaks.
(3) Leaks at the bottom of the drum. This is often overlooked but can occur if debris such as stones, screws, or metal pieces remains on the warehouse floor. These objects can become embedded in the drum during unloading. Improper forklift operation, such as hitting the drum's base, can also cause leaks.
II. Countermeasures to Address the Issues
(1) The quality of the steel drum is fundamental to preventing leaks. Manufacturers must ensure that drums meet safety standards, with at least five layers, ideally seven. The sealing material should be uniform and strong, with no weld defects. Proper handling during loading and unloading is essential to avoid dents, especially around T-joints.
(2) During the sealing process, operators must work carefully, avoiding rapid movements that could cause uneven pressure and lid leakage. Sealing wheels should be adjusted regularly, and worn-out parts replaced promptly. Workers in sealing roles should remain in their positions, and new employees must receive thorough training before being assigned to the role.
(3) Nitrogen should only be filled after the calcium carbide has cooled to room temperature. A two-step nitrogen filling process is recommended: first, check for leaks, remove faulty drums, and then fill the remaining ones. Pressure should be maintained at a stable level, avoiding excessive force when tightening bolts to prevent gasket damage.
(4) Warehouses storing calcium carbide must be clean and free of debris. Forklifts should be operated gently to avoid damaging the drums. Before painting, any dust or residue should be removed to maintain a clean exterior.
(5) Gas seal inspections should be conducted one week after nitrogen filling. Based on past experience, drums with slightly collapsed lids are ideal for testing. Most drum covers are tightly sealed, but soap solution used in testing should be rich in foam. When the pressure reaches the required level and remains constant for over three minutes, careful observation is needed to detect any leaks. If the pressure gauge drops, further checks should be made at the base, T-joints, and welds. Inspectors must remain focused and follow strict procedures to ensure safe transportation of exported calcium carbide.
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