Maintenance
Graphite stem seals are being mounted one by one .
terms of boosting plant uptimes , this trend can add extra complications to the shutdown , notes Mr Zegers . “ This development has been exacerbated by the Covid pandemic , when plants were understandably reluctant to have people on site unless absolutely necessary . Whatever the cause , the result can be increasing wear and tear on valve components , meaning that simple repair jobs can become more complex and time-consuming .” From time to time , Mr Zegers also faces unexpected issues , such as corrosion in valves which had previously gone from shutdown to shutdown without needing maintenance . “ In such cases it could well be that the process medium flowing through that particular pipework has changed since the time the plant was set up . Or perhaps the valve was not properly selected . That could be the type of valve , the ( internal ) materials or the Cv value in the case of a control valve . During the specification process it is most important to consider all the materials that the plant designer indicates might potentially be flowing through the valve . Simply looking at the pressure and temperature ranges is certainly not enough .”
While discussing media , Mr Zegers notes that another issue which is occurring more and more regularly is failures in trunnionmounted ball valves . “ The problem here seems to be caused by the medium in the installation such as certain types of crude oil . If oil conglomerates behind the seats it can cause the valve to stick and / or lead to in-line leakages .” Fortunately there are solutions , continues Mr Zegers . “ Options could be to fit a steam jacket or to consider using a different type of valve . For example , a rising-stem ball valve .” Asked about the origins to this type of problem , Mr Zegers indicates that refineries may have switched to a different supply source . “ Crude oil is not a consistent commodity . Each well can produce oil with unique characteristics such as impurities and in fact even oil from the same well can change from sweet to sour over the course of time . I have seen hydrogen ( sulphide ) cause major issues with valve materials such as chrome or nickel plated balls , for example .”
Reducing bottlenecks
Whatever the challenges , Mr Zegers remains passionate about his job and is determined to keep finding new ways to help maintain valve populations in perfect working order . “ As stated , it can take quite a time for manufacturers to produce parts for certain valves . So one solution going forward could be to make more use of additive manufacturing . Even better would be if the repair shop itself could be authorised to 3D print the necessary parts , thereby eliminating transport delays . This is an option which I would really like to discuss with the valvemakers .” Another benefit might accrue if manufacturers could agree on standards for components such as valve stems , suggests Mr Zegers .
Metal tags with sections that can be punched out facilitate the safe handling of valves during overhaul
Dye penetrant testing can reveal defects , such as in this RTJ end flange on a valve body
30 Valve World April 2023 www . valve-world . net