Due to the lack of national standards for the design, manufacture, installation, use, inspection and modification of domestic industrial pipelines, there are many defects in the pipeline construction and installation process, and the pipelines cannot be inspected internally like pressure vessels. The external inspection is mainly based on macroscopic inspection, and if necessary, wall thickness measurement is used for corrosion monitoring. The macro inspection project includes four parts. Whether the heat preservation and anti-corrosion layer are intact; the corrosion status; whether there is leakage at the tower, the bottom of the reactor and the flange joint; whether there are macroscopic cracks on the surface; whether there is abnormal deformation and vibration;
The comprehensive inspection is mainly based on macro inspection and wall thickness measurement, and non-destructive testing or other test items may be used if necessary. Before measuring the wall thickness, the corrosion characteristics of the medium in the pipe and the flow direction during operation should be cleared, and the parts that are susceptible to erosion and corrosion should be determined, and at least 3 points should be selected for each part. All parts with reduced wall thickness should be measured. To. For the pipeline, the elbow (and the sampling ratio of the bottom of the tower and the reactor is 100%, and the pipeline is not less than 50%.
(1) Turbulence zone at fixed-point thickness measurement parts: elbows, flow diversions, confluence parts, etc .; stay zone: safety valve connection, drainage condensate connection, bypass connection, etc .; impact zone: tower, reactor bottom, connected to both ends of the elbow Eroded straight pipes, outlets of pumps, compressors, furnaces, regulating valves and their manifolds, parts with unstable flow conditions greater than 5m, etc .; water, steam and chemical injection parts; each circumferential weld On both sides.
(2) Non-fixed-point thickness measurement The location of the corrosion rate that is found to be abnormally large and the wall thickness close to the scrapped location after the inspection is determined.
According to the macro inspection, it is suspected that there are obviously corroded parts. Judging from the thickness measurement results, the eroded part of the elbow and the straight pipe connected to it is not easy to determine, and it is best to solve it by adding measuring points. For measuring points where the corrosion rate is significantly greater than other parts, marks should also be made and monitored regularly.
Since the pipeline cannot be inspected internally, it is not allowed to do so due to economics and duration. Therefore, only random inspections are possible. In principle, at least one piece of each welding port of the pipeline that transports flammable, explosive and toxic media should be taken; if cracks are found, the inspection should be expanded according to the situation. The following parts must be sampled. Welded joints with severe geometrical discontinuities; welded joints suspected of local corrosion; pipe fittings with severely corroded pits during macro inspection and thickness measurement to determine the extent or morphology of corrosion; internal scaling or clogged parts.
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