Occasionally process plant operators need to modify the operating parameters of the plant in their charge. Typically this could be in order to reduce emissions or increase plant capacity and can result in a requirement to re-rate installed items of process equipment. FCL engineers have the necessary experience and tools to assist in the re-rating process to ensure that plant safety is not compromised. When project objectives can be achieved by re-rating substantial reductions in capital expenditure and plant downtime can be achieved which often far outweigh the cost of FCL services.

Case Study: In order to increase pipeline capacity a North Sea facility operator had identified that an increase in compressor discharge cooler maximum allowable working pressure (MAWP) was required. Replacement would be time consuming and prohibitively expensive. FCL were engaged to examine the feasibility of achieving the required increase in the air cooled heat exchanger MAWP from 115 bar g to 130 bar g.

Although Code calculations were sufficient to demonstrate the adequacy of the header box design, the geometry of the stiffened process nozzle transitions fell outside published code rules and a three dimensional finite element stress analysis of one of the headers was necessary in order to substantiate the design.

The results of the finite element stress analysis were validated by strain gauge measurements taken on the transition side walls. Correlation between the strain measurements and the results of the stress analysis was achieved.

A comprehensive report was prepared by FCL engineers and submitted to the certifying authority for appraisal in support of the proposed increase in MAWP to 130 bar g. Approval for the increase in MAWP was granted without recourse to further work.