Softly, softly catchee muckee
01 February 2009
Cleanliness is critical for steam lines; the smallest of dirt particles can do substantial damage to the blades of a steam turbine, so thorough cleaning is essential. The process requires careful pump control to ensure the safety of personnel and to protect assets - a good enough reason why SABSCO chose soft starters over DOL starting on one of its recent Middle Eastern projects
Newly constructed high-pressure steam lines are thoroughly cleaned and thermally cycled prior to commissioning by blowing superheated steam through them to clear debris left during the construction process. Debris often encountered includes welding scale, swarf, nuts, bolts and general detritus but, in fact, larger objects are frequently flushed out during this process. Indeed, it is not uncommon to find welding rods and, according to Steam and Air Blowing Service Company (SABSCO) operations manager, Steve Smith, even blocks of wood and tools.
SABSCO offers a highly professional steam line cleaning service to the global petrochemical and power generation industries, and its expertise is particularly sought where steam turbines form an integral part of the installation. Monitoring the results of the cleaning process is a rather sophisticated operation. To do this, a highly polished, mirror-finish ‘target plate’ is positioned within the steam lines during the blow-through and when removed, is microscopically inspected for signs of ‘impacts’. A typical specification is no more than four impacts of not more than 0.1mm in diameter.
On a recent ethylene plant project in Saudi Arabia, where the ambient temperature frequently exceeds 45ºC, the thermal cycling time was unacceptably long and SABSCO was determined to reduce this dramatically. The company decided to inject 20 tonnes per hour of demineralised water at ambient temperature and pressures of up to 28bar; this was expected to provide accelerated quenching, thus reducing the overall cleaning cycle time. In order to achieve an acceptable level of reliability and redundancy in this hostile environment, this procedure required two 30kW centrifugal pumps with a 30m lift, feeding into a single manifold.
Simple direct-on-line (DOL) or star-delta starting was out of the question as a 20 second start-up period was necessary to enable the connecting pipe work to be monitored for minor leakages, and to facilitate a rapid and controlled shut-down if necessary. To achieve the necessary degree of control, SABSCO selected two Series 58-400-0-S motor soft starter units from Softsart UK.
The nature of this special duty dictated that the pump rig be portable, so the soft starters were supplied by Softstart ready installed in a control panel, which contained additional motor control equipment. The client also requested rapid delivery, which was also successfully achieved, according to Mr Smith. “I have used products from Softstart UK on many occasions over the past few years and knew they could deliver. The equipment has proved to be reliable and rugged, which is exactly what we need in the environments in which we work. Quality of service, from enquiry to after-sales, is very high on our list of priorities and we continue to experience this from Softstart. This new and now proven technique has given us and our client clear schedule benefits.”
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