Before we talk about open drain system, lets discuss first about FPSO and Fix Platform. Since two of kind offshore structure have different on it, but not totally change on concept. Actually, FPSO or Floating Production Storage Offloading is ship that has top side module to process oil from sea bed through riser. Other word, FPSO has characteristic as ship let me say it has trim by default of ship. And Opposite with Fix Platform, Fix platform regardless trim on it’s building. bellow picture is sample of trimmer on ship.
And what is drain? As we know, drain is line to capture water on deck and will coalesce into header and throw out of ship (if it is just water). But in process system, not only in oil and gas side, drain segregate into 2 kind, Open drain and Close drain. The main different is fluid contain, for open drain may be just water (or little of bit oil contain on water) and pressureless on it. and close drain my be contain oil, water, gas and has pressure. Due to different principle on function, open drain and close drain has different header. Actually, both of drain have to use slope and it is mandatory. Although close drain has pressure. Even in hazardous and non hazardous area, two of drains have same application.
From clue issues, open drain has rodding point tundish, open drain box, header, slope. and for close drain without tundish, and open drain box also use rodding point like blind flange for some spot whose advance parameter.
Let me back application on FPSO and Fix Platform. Slope is how many length of pipe route and will bu down if the number already reached. In math we say gradient, so every slope will have same angle. Slope that capture on P&ID is minimum value. Slope indicate with 100 : 1, 50 : 1, and so on. 100 mm route of pipe, has decrease height 1 mm. Because FPSO has slope, pipe slope on it will different especially the number of slope that opposite position with slope of ship, the number will be bigger, for example by default has 100 : 1, so after we change position, it will be 50 : 1. Different with fix platform, fix platform has typical slope on close or open drain.
Rodding Point :
Rodding Point has function to clean any blocking on the line. For open drain, rodding point used to drain liquid that trap on deck. Why it has circle of shape? my fooling answer, if we open the cover, and we are careless and wrong place of cover, the cover don’t throw on pipe, because any position of cover can’t make it fall into the header, ignore it. Just joke……
Tundish is piping component to prevent flow, on offshore system, generally, tundish is applied on top of deck and pipe will be higher min 50 mm, slightly like reducer. Tundish can be rodding point, so if any liquid trap on deck we can flow it into tundish.
Open Drain Box
Bellow sample of open drain box on street.
And the important of close drain. Close drain prevent any leak from vicinity. it means close drain will connect flange to flange. Especially from process equipment. Any liquid that indicate with free drain on P&ID, if any pocket on routing and we can’t ignore it, after process allow to use pocket, we need to provide drain. It just flange, valve and hose connection. The header on edge used to connect flashing connection, same with drain but on high point of header. So we can purge on that line well if any blocking on it.