In urea plants, HP equipment are inspected on regular basis during planned turnarounds, however the interconnecting HP process lines in general, do not always get the same attention. This lack of attention is not justified. It is well established in the chemical industry that the failure of pipelines is more likely to occur than the failure of static process equipment.
The main reason is the fragmentation of responsibilities throughout the total life cycle of pipelines; i.e. different groups are responsible for design, construction, operation, inspection, maintenance, modifications, repairs, and finally decommission. This is much more fragmentized compared to (critical)static process equipment.
Another difference is the wide spread of pipelines across the plant, leading to difficulties in allocating responsibilities, especially when pipes crosses boundaries of plants.
Finally it is almost impossible to do internal visual inspections of pipe lines compared to static equipment which makes the integrity assessment of piping much more difficult.
Below paper describes the failure and study of that in Abu Qir urea plant (also included in the UreaKnowHow.com Urea Incident Database.