Preliminary Study on the Causes of Failure in Identifying Calcium Carbide Steel Drums
Huang Rui
Calcium carbide is a highly flammable and explosive material, making its safe handling and packaging critical. China's annual export volume of calcium carbide exceeds 3 million barrels, but incidents of explosions due to poor packaging have occurred at both domestic and international ports, resulting in significant economic losses. Proper identification of dangerous materials in calcium carbide steel drums is essential for maintaining the reputation of Chinese exports, preventing financial damage, and ensuring safety.
The typical packaging for calcium carbide is an open steel drum, classified as a dangerous package of Type II. Unlike other open drums, calcium carbide drums must be tightly sealed to prevent leaks. This sealing requirement is a key factor in the inspection process and often highlights unqualified conditions. In this paper, the author provides a brief analysis of common issues encountered during inspections, aiming to spark discussion among professionals in the field.
I. Analysis of Failure Reasons
The primary focus of identifying calcium carbide steel drums is on their appearance and airtightness.
Common issues in visual inspections include rough surfaces on the drum cover and severe deformation of the top. A rough paint surface usually occurs when calcium carbide powder becomes airborne during filling and isn't cleaned properly before painting. This issue is relatively easy to address. However, deformation at the top of the drum is more complex, typically caused by excessive nitrogen pressure during the nitrogen charging process. To prevent this, the pressure should not exceed 30 kPa, and once the desired pressure is reached and stabilized, the nitrogen filling should stop immediately. Operators must be trained to monitor pressure levels carefully and avoid relying solely on experience.
Gas seal failures are more complex and can be categorized into several main causes:
(1) Air leakage from the air hole. This is mainly due to poor elasticity or uneven thickness of the sealing gasket. Additionally, applying too much force when tightening the bolts after nitrogen filling can cause the gasket to tear, leading to leaks.
(2) Leaks at the curled and sealed sections. Three main factors contribute to this: first, if the sealing compound is not evenly mixed or applied, gaps may form during crimping; second, prolonged use of the sealing machine can wear down the sealing wheel, reducing its effectiveness; third, excessive force during the sealing operation can result in uneven sealing and subsequent leaks.
(3) Leaks at the bottom of the drum. This is often overlooked but can occur when debris such as stones, screws, or metal pieces on the warehouse floor are not cleaned up before loading. These objects can become embedded in the drum’s base during unloading. Additionally, improper forklift handling, such as hitting the bottom of the drum, can also cause leaks.
II. Countermeasures to Address the Issues
(1) Ensuring high-quality steel drums is crucial for preventing leaks. Manufacturers must adhere to strict quality standards for dangerous goods packaging. The drums should have at least five layers, with seven being ideal. The sealing compound must be uniform and strong, and welds should be free of defects. During loading and unloading, care must be taken to avoid impacts that could damage the drum, especially at the T-joints.
(2) Operators involved in sealing must follow precise procedures. Sealing speed should be controlled to avoid uneven pressure that could lead to lid leaks. If the sealing wheel is large, it should be adjusted or replaced when necessary. Workers in sealing positions should remain consistent, and new employees must receive thorough training before being assigned to these roles.
(3) Nitrogen should be filled only after the calcium carbide has cooled to room temperature. Typically, two rounds of nitrogen filling are performed. After the first round, the gas seal is checked, and any leaking drums are removed. Once confirmed to be leak-free, the second nitrogen filling ensures proper sealing and nitrogen content. The pressure during filling must be stable and not too high to prevent lid deformation. Avoid excessive force when tightening the bolts post-filling to prevent gasket damage.
(4) Warehouses storing calcium carbide must be clean and free of debris like stones, iron blocks, or screws. Forklift operators should handle drums gently to avoid collisions that could cause leaks. Before painting, the drum surface should be thoroughly cleaned to remove dust and calcium carbide powder, ensuring a smooth and clean finish.
(5) Gas seal identification should be conducted one week after nitrogen filling. Based on past experience, drums with collapsed lids are typically selected for testing. Drums with slightly deformed lids are usually well-sealed. For the soap solution test, a rich foam is used. When the required pressure is achieved and maintained for over three minutes, the inspector should closely observe the pressure gauge and check for any signs of leakage, particularly at the bottom, T-junctions, and welds. Inspectors must stay focused, avoid distractions, and ensure accurate results to guarantee the safe transportation of exported calcium carbide.
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