How to replace sulfuric acid pipelines
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Carbon steel pipes are used for pipelines carrying concentrated sulfuric acid. If a leak occurs in a certain section of the pipeline and it needs to be repaired, how should it be cleaned and replaced to meet the required standards? Once, on-site, I saw a leak at the elbow of a sulfuric acid pipeline; after removing the insulation to inspect it, I found that the elbow had been severely corroded. The best option is to cut off the damaged elbow and replace it with a newer one. On-site handling involves introducing nitrogen at one end of the pipeline, forcing concentrated sulfuric acid into the storage tank from the other end, then opening the side pipe of the tank and continuing to purge it with nitrogen. After a period of time, if analysis shows no flammable gases, work can be approved. Due to the sulfuric acid remaining inside the tube, the welding quality was very poor. Some suggested rinsing the pipes with clean water, but the site supervisors believed that water washing was not possible, as it would cause further corrosion of the pipes. So, for hot work, it is required that the medium at the site of hot work be replaced and cleaned to an acceptable standard – is it sufficient to simply purge it with nitrogen? There is a large amount of concentrated sulfuric acid remaining on the wall of the pipe; although there is no risk of combustion or explosion, it still has an impact on the quality of welding. Moreover, it poses a risk of chemical burns to the workers as well
The essence of displacement is to ensure the absence of flammable gases and to minimize pipeline corrosion. Different pipe diameters are considered; for cases where concentrated sulfuric acid flows continuously at full capacity, some manufacturers opt for welding right after the acid is drained (with whether to carry out simple treatment determined based on actual conditions), without performing any displacement process ； If it will be out of use for an extended period and hydrogen may still be present, it is necessary to purge the area; nitrogen or compressed air can be used for this purpose. In the event of residual acid, patch welding or sleeve welding can be employed ； If residual acid affects the welding quality, appropriate methods must be used to address it. . ）
In carbon steel pipes with a high residue of sulfuric acid, welding can cause a fire; this is based on practical experience
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