Orifice plates for compressor anti-surge application


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Orifice assembly for 30" pipe lines, we have very limited upstream and down stream straight length, as per ISO5167 or AGA3. Experts can you suggest what is the best solution. since it is for major oil company only proven solution will be accepted. Our pipe line is 30

As long as the orifice is ONLY being used for anti-surge control on a typical pipeline compressor, you probably do not need the "textbook" upstream and downstream straight pipe lengths. Now, it has been at least 30 years since I have designed an anti-surge control loop (we were still using 4-20 ma discreet controllers then), but for the suction flow measurement we usually used the compressor inlet eye as the primary flow element. This provided sufficient accuracy for pipeline compressor stations. The control line was typically set at about 10% higher flow than the actual surge line. As long as your client accepts that setting, an inlet eye differential pressure transmitter should be acceptable. You may need to dampen (filter) the signal from the transmitter, since it will likely be "noisy." If the compressor has a high compression ratio, for say gas re-injection, then this may not be a good solution. But then you would likely be using smaller diameter pipes since the pressures would be higher.
averaging pitot type probes work somewhat better in limited confines.

NPS 30 plates can be used certainly, but are an installation problem because of the flanges and the plate thickness.