The technology behind turbine bypass explained
A turbine bypass routes steam around the turbine during start up and after a trip, so the boiler can keep running while the turbine is offline. There are assumptions circulating about turbine bypass that do not hold up under closer examination. Anyone looking into turbine bypass quickly runs into a choice that goes beyond picking a catalogue number. Steam is a demanding medium because pressure and temperature rise together and the medium can change phase within the same line. A pressure reducing station brings steam pressure back to the level the consumers require and holds that pressure stable under varying demand. An emergency stop valve shuts off supply in a hazardous situation, and closing time there is a safety parameter rather than a comfort requirement. We regularly see that a small change in the execution of turbine bypass makes a large difference to maintenance frequency. What weighs heaviest on turbine bypass in practice is the combination of temperature and differential pressure, not either one alone. On turbine bypass we always check the full operating envelope, including start up and shutdown. In superheated steam the temperature sits above saturation, and soft seats and ordinary packings are then no longer usable. On a boiler, blowdown valves control the salt content of the boiler water, with continuous blowdown for fine control and periodic blowdown for sludge at the bottom. With turbine bypass the difference between a good and a mediocre solution often sits in details that do not show on a drawing.
Turbine bypass and the decisive technical choices
The bypass has to absorb a very large pressure drop, which normally calls for multistage trim to control noise and erosion. With turbine bypass it pays to include phase changes in the medium, because those sharply increase the load on the seal. For turbine bypass this means that construction and operating conditions cannot be judged separately. Steam is usually desuperheated in the same station, because the condenser cannot accept steam at full temperature. A turbine bypass routes steam around the turbine during start up and on a trip, and that valve has to handle a large duty within seconds. Condensate carried along in a steam line causes erosion and water hammer, and both attack a valve faster than the steam itself. A desuperheater injects water into the steam flow to bring temperature back to just above saturation, where atomisation quality determines the result. Fast and reliable opening is essential, since the alternative on a trip is releasing steam to atmosphere. On steam we always advise a condensate drain upstream of the valve, because it is the cheapest life extension available. On commissioning we record set pressure, closing time and test results, so the plant can be shown to run within specification. Operating conditions govern the service life of turbine bypass far more strongly than the nominal figures on a datasheet. With turbine bypass the seat is the component that determines performance, and the body is rarely the limiting factor.
Turbine bypass in demanding installations
Turbine bypass systems are used in power plants, combined cycle installations and industrial cogeneration. Boiler houses, combined heat and power plants and district heating together form the largest application area for these valves. In process industry steam is used for heating, stripping and sterilisation, and each of those duties sets its own requirements. We see demand for turbine bypass rising in hydrogen and ammonia projects, where tightness requirements are high. On replacement we always check the existing installation dimensions for turbine bypass, so the pipework can stay untouched. For turbine bypass the sector determines which documentation and tests belong with the delivery. The application range of turbine bypass runs from simple utility duty to heavy process plant, with a corresponding difference in execution. In power generation these valves sit on the critical paths around boiler and turbine, where downtime costs money immediately. Our market is project driven and international, and we deliver worldwide to installers, EPC contractors and end users. Our customers use turbine bypass in positions where a failure has immediate consequences for production. On project supply we record per position which execution of turbine bypass was delivered, including materials and tests.
How to select turbine bypass without mistakes
If a simpler type will do the job, we say so on turbine bypass, even when that means a smaller order. A steam test device makes it possible to test the operation of safety valves while the plant stays in service. On steam applications we always ask for pressure and temperature upstream and downstream, because pressure drop defines the trim construction. At large pressure ratios we use multistage or perforated trim to keep noise and erosion within acceptable limits. For turbine bypass total cost of ownership weighs more than purchase price, certainly when replacement has to happen during a shutdown. The required leakage class often drives the choice around turbine bypass more strongly than the budget does. We never recommend a heavier execution of turbine bypass than needed, because over specification only raises price and lead time. For turbine bypass we ask as standard for DN, pressure class, medium, temperature and required actuation. Insulation around a steam valve should leave the actuator clear, because overheating of the actuator is a common cause of failure. PRUSS is strongly represented in this segment with valves for steam, boiler, turbine and gas turbine duty. For an accurate quotation we need the nominal diameter, the pressure class, the medium, the operating temperature and the required actuation. The right choice around turbine bypass starts with a full set of process data rather than with a request for a price. The cleaning and flushing procedure counts too on turbine bypass, because it can be more aggressive than the process itself.
Ordering turbine bypass from Dutch Valve Vision
We supply turbine bypass as a loose product or as a fully assembled unit with actuator and accessories. Dutch Valve Vision supplies special valves for special applications from its base in Monster, the Netherlands, with QUADAX and PRUSS as the core brands in the programme. For turbine bypass you can come to Dutch Valve Vision for the selection, the delivery and the support afterwards. We handle an enquiry for turbine bypass on its technical merits rather than as a price request that only produces a number. Dutch Valve Vision stays available after delivery of turbine bypass for technical questions and for parts. Lead times depend on the execution, because a standard size from a running series behaves very differently from a valve in an exotic alloy with NACE certification. We quote a realistic lead time rather than an optimistic one, because a missed delivery date costs more than an extra week in the planning. We work on turbine bypass under a KIWA ISO 9001 certified quality system, which safeguards traceability. A tag plate with project data belongs with turbine bypass as standard where the project requires it. We record which execution of turbine bypass was delivered, so a follow up delivery or spare part matches exactly later on. Even when the specification for turbine bypass is not yet finalised, you can bring the question to us. Send us your DN, pressure class, medium and temperature at sales@dutchvalvevision.com, or call +31 (0)70-2210560 to speak to a specialist.
Frequently asked questions about turbine bypass
What exactly does turbine bypass mean?
Steam is a demanding medium because pressure and temperature rise together and the medium can change phase within the same line. On a boiler, blowdown valves control the salt content of the boiler water, with continuous blowdown for fine control and periodic blowdown for sludge at the bottom. In superheated steam the temperature sits above saturation, and soft seats and ordinary packings are then no longer usable. Condensate carried along in a steam line causes erosion and water hammer, and both attack a valve faster than the steam itself. We always explain why we arrive at a particular recommendation on turbine bypass, so you can follow the reasoning yourself. For turbine bypass a good specification up front is cheaper than a correction afterwards. Once turbine bypass is correctly specified it disappears from the fault list, and that is exactly the intention. We work as a technical supplier rather than a catalogue reseller, which means we carry out the selection ourselves on the basis of medium, pressure, temperature and code requirements.
Which executions of turbine bypass are available?
On commissioning we record set pressure, closing time and test results, so the plant can be shown to run within specification. A turbine bypass routes steam around the turbine during start up and on a trip, and that valve has to handle a large duty within seconds. A desuperheater injects water into the steam flow to bring temperature back to just above saturation, where atomisation quality determines the result. The bypass has to absorb a very large pressure drop, which normally calls for multistage trim to control noise and erosion. We see this come back regularly in enquiries about turbine bypass, and the answer is rarely a single sentence. On turbine bypass we prefer a well founded answer to a fast one that turns out to be wrong later. The balance between required tightness and available operating force is a recurring tension on turbine bypass. Our market is project driven and international, and we deliver worldwide to installers, EPC contractors and end users.
Which materials are used for turbine bypass?
PRUSS is strongly represented in this segment with valves for steam, boiler, turbine and gas turbine duty. A pressure reducing station brings steam pressure back to the level the consumers require and holds that pressure stable under varying demand. Steam is usually desuperheated in the same station, because the condenser cannot accept steam at full temperature. An emergency stop valve shuts off supply in a hazardous situation, and closing time there is a safety parameter rather than a comfort requirement. The answer to this question on turbine bypass changes as soon as the medium or the temperature changes. The answer on turbine bypass depends strongly on operating conditions, which is why we always ask for those first. That principle explains why turbine bypass behaves differently from a standard execution under heavier duty. Dutch Valve Vision operates under a KIWA ISO 9001 certified quality system, which in the RFQ stage of chemical and offshore projects is usually a hard requirement.
What should I watch technically on turbine bypass?
What should I watch technically on turbine bypass?
Which applications call for turbine bypass?
Boiler houses, combined heat and power plants and district heating together form the largest application area for these valves. In process industry steam is used for heating, stripping and sterilisation, and each of those duties sets its own requirements. In power generation these valves sit on the critical paths around boiler and turbine, where downtime costs money immediately. Turbine bypass systems are used in power plants, combined cycle installations and industrial cogeneration. This is one of the points on turbine bypass where suppliers differ most clearly from one another. Our experience with turbine bypass comes from projects in chemicals, power generation, technical gases and offshore. Demand for turbine bypass reaches us mainly from projects where the standard range falls short. Our customers work in chemicals, petrochemicals, pharmaceuticals, power generation, offshore and in hydrogen and ammonia projects.
What determines the price and lead time of turbine bypass?
Lead times depend on the execution, because a standard size from a running series behaves very differently from a valve in an exotic alloy with NACE certification. We come back with a proposal that explains why we recommend a particular execution, including the alternatives we considered. We quote a realistic lead time rather than an optimistic one, because a missed delivery date costs more than an extra week in the planning. If you have an existing tag plate or serial number, send it along, because that lets us work directly from the original configuration. If you are unsure about this on turbine bypass, we are glad to put the question alongside the actual process data. In most projects turbine bypass turns out to be less standard than it first appears. We think along on the spare parts strategy for turbine bypass, so critical positions stay covered. You can reach us on +31 (0)70-2210560 and at sales@dutchvalvevision.com, and our office hours are Monday to Friday from 09:00 to 17:00.
What about maintenance and spare parts on turbine bypass?
Documentation such as material certificates, test reports and declarations is supplied as standard, matched to what the project requires. Insulation around a steam valve should leave the actuator clear, because overheating of the actuator is a common cause of failure. We keep spare parts and overhaul kits mapped per project, so that a breakdown does not start with a search from scratch. For shutdowns and turnarounds we look at accelerated routes, and in those cases we are honest up front about what is and is not achievable. The answer to this question on turbine bypass changes as soon as the medium or the temperature changes. In most projects turbine bypass turns out to be less standard than it first appears. Material certificates and test reports are supplied with turbine bypass, matched to what the project requires. What defines us is that we would rather spend an extra half hour on the specification than ship the wrong valve that comes back two months later.
How do I request a quotation for turbine bypass?
A P&ID, a datasheet or even a photograph of the existing installation often helps us faster than a long description. For an accurate quotation we need the nominal diameter, the pressure class, the medium, the operating temperature and the required actuation. On repeat orders we record the configuration, so a follow up delivery is identical to the first and installation holds no surprises. Please also state the connection standard, the required leakage class and any project requirements such as NACE, PED or ATEX. For turbine bypass a good specification up front is cheaper than a correction afterwards. This is one of the points on turbine bypass where suppliers differ most clearly from one another. For repeat orders of turbine bypass we record the configuration, so a follow up delivery is identical to the first. We are based at Vlotlaan 641, 2681 TZ Monster in the Netherlands and can be reached on +31 (0)70-2210560 and at sales@dutchvalvevision.com.