Weekly topic (12.5-12.11): Discuss the areas of corrosion that have occurred on the equipment and their causes

First, here are the details: 1. Name of the unit: Delayed coking. 2. Location of corrosion: Corrosion and perforation at the extraction elbow in the top circulation system, which led to a major fire. 3. Cause of the incident: High sulfur content in the feedstock. 4. Emergency measures: Initial inspections showed that the wall thickness of the pipes was very low; clamps were installed at the elbows, sleeves were added, and glue was used to maintain operations for over 6 months. It was not until a rupture occurred during the shutdown that the oil flowed down along the tower wall and dripped onto the flanges of the hot oil and gas, triggering a massive fire. Water was supplied through the inlet of the gasoline pump (the water washing line) and sent in a cooling return flow into the distillation tower; since the tower was already shut down, it was the return flow from the shut-down side stream that caused the fire. The water pushed the oil out of the distillation tower, thereby extinguishing the fire. Fortunately, no equipment damage occurred, and the losses were minimal. It was found later that the cracked area of the elbow was thinner than paper. Permanent solution: Replace the top circulation extraction line, upgrading its material to 316L; it should be replaced every three years. There are no dual valves from the top circulation extraction point to the pump inlet and outlet.

1. Device name: Antioxidant device. 2. Corroded areas: Corrosion cracks have appeared on the coiled tubes and welds of the concentrated mother liquor tank. 3. Cause of the problem: It may be due to the presence of Cl ions; since this issue arose recently, there are no effective solutions yet. 4. Immediate corrective actions: Production must be continued, as the tank head is still leaking; the external coiled tubes need to be replaced with internal ones. 5. Permanent solution: It is expected that, after consideration by the company’s management, stainless steel tanks made of 316L material will be used instead

Sulfur recovery unit； Sulfur cooler or exhaust pipeline ； Water is produced during the formation of sulfur, and it reacts with SO2 to corrode pipes or equipment. The other reasons are also unclear

1. Equipment name: Catalytic cracking. 2. Corroded area: The outlet pipe at the upper part of the oil-gas separation vessel in the fractionation tower. 3. Cause of corrosion: High sulfur content in the feedstock, as well as acidic water from external sources. 4. Remedial measures: Fortunately, it was detected in time, and all operations involving fire were halted. Seal it with iron mortar to maintain it temporarily. Increase routine inspections of such areas. Strictly control the amount of oil pressure applied to external devices, adhering to the principle of small amounts applied continuously. 5. Permanent solution: During shutdowns, strengthen the thickness testing of similar pipelines and containers, and replace the materials to suit the conditions associated with high-sulfur crude oil.

1. Device name: Atmospheric pressure device. 2. Corrosion site: Corrosion and leakage at the upper part of the atmospheric pressure tower. 3. Cause of occurrence； 1. The raw materials contain a high level of sulfur. 2. Our factory does not have any catalytic devices, and management does not pay enough attention to electrodesalination, so it has not been in use for a long time. 3. The thickness of the equipment was not measured, which creates potential risks that could lead to accidents. 4. The inspection work was inadequate; it was not until gasoline was found at the base of the tower that someone went up to check it. 4. First-aid measures: Stop work urgently in accordance with the plan. 5. Radical treatment: The upper 6 meters of the atmospheric pressure tower were replaced based on the extent of corrosion.

As a supplementary note, the permanent solutions taken included replacing the upper 6 meters of the atmospheric pressure tower based on the extent of corrosion, installing electrical desalination systems, reorganizing the inspection routes, and including thickness measurements of various containers as part of the annual inspection routine

1. Device name: DCC 2. Corroded area: Heating pipeline of the flue gas system 3. Cause of corrosion: The heating pipeline is made of stainless steel, and the flue gas contains sulfur. After the heating pipeline was installed, the valves were closed, which led to a drop in temperature; this caused low-temperature sulfur corrosion of the stainless steel, resulting in cracks in the pipeline. 4. First aid measures: Locate the starting and ending points of the crack, drill holes and then weld them, or simply cover it with a large box. Permanent solution: Keep the heating pipeline slightly open to maintain a certain temperature in it and avoid low temperatures.

Device name: Catalytic cracking. Affected area: Expansion joint at the top of the settler. Cause: Wear through of the catalyst. Immediate remedy: Reduce production volume and install clamps. Permanent solution: After 4 months, take advantage of the scheduled shutdown for maintenance and replace it

1. Equipment name: Utility systems. 2. Corroded areas: Welds or elbows in the unpurified air lines. 3. Cause of corrosion: Water present in the unpurified air, which reacts with oxygen over time to cause rusting. 4. First aid: Seal the leak urgently using clamps. Preventive measures: For older equipment, it is necessary to conduct more thorough thickness checks of the relevant pipelines during maintenance; any issues found should be addressed by welding repairs or replacing the pipelines promptly

1. Equipment name: Atmospheric and Vacuum Distillation Unit 2. Corroded area: Heat reflux elbow in the third stage of distillation 3. Causes of corrosion: Naphthenic acid corrosion leading to thinning, as well as erosion due to high flow rates 4. Emergency measures: Reduce the operation capacity of the unit and stop using the heat reflux system 5. Preventive measures: After upgrading the materials, replace them regularly and conduct thickness measurements