Piping Design Guide -Vertical -Vertical Drums
Vertical Vessels Vertical vessels can be classified into the following categories Columns Drums Reactors Columns are used in the process units for fractionation and stripping. Drums are used in the process units un its for intermediate liquid collection, product storage, separation of two different products of different densities, surging, reflux accumulation and de-aeration. Reactors are used in the process units to contain catalysts that promote chemical transformation of feeds or to remove undesired materials from feed. Vertical Drums Locating the drum The piping designer should economize piping interconnections between the the drum and its adjacent equipments ( pumps , condensers, heaters etc.) when locating the drum. The following documents are needed to locate the drum on the plot plan. P&ID Process Vessel Sketch Plot plan Piping & Plant Layout Specification (P-GS-PL-003-0A). The drum is located on the plot plan as per the process sequence dictated by the P&ID. Small drums can be placed on stand alone structures or grouped together with related equipments in an enclosed structure. Large drums need a civil foundation of their own. Drums are best located on either side of the pipe rack , serviced by auxiliary roads for maintenance access. Vessel transportation , erection and other constructibility issues should also be looked into while finalizing finalizing the location of the vessel. Adequate space must be provided around the drum for operator movement and maintenance access. Locating close to an access road to reduce maintenance efforts. Inter-distances between adjacent equipments are fixed as per Table 5 of Piping & Plant Layout Specification . The Bottom Tan Line elevation is fixed by the P&ID. The same may be increased to facilitate piping and equipment layout in consultation with the Process group. After the drum has been located on the plot plan, the following jobs are carried out.
Drum elevation review and support selection Nozzle orientation Platform and access requirement Support cleat location detailing Lifting lugs and earthing lugs location planning Finalizing Vessel Name Plate location Drum elevation review and support selection The Bottom Tan Line elevation fixed by the P&ID is the minimum elevation required for NPSH of the bottoms pumps. This may be increased in consultation with Process Group for the following . Operator Access - Proper head room clearance should be available for safe operator access to the drum. Maintenance Access- Proper maintenance access clearance should be available for safe movement of maintenance equipment around the drum. Minimum clearance as per piping layout Bottom nozzle size - The bottom nozzles are connected to the bottom head with a straight pipe piece and a 90( elbow. This lowers the clearance available below the bottom of the elbow Bottom head details ( elliptical , hemispherical etc. )Hemispherical head has a depth twice as compared to elliptical ( 2:1) This will change the center line elevation of the bottom nozzle and consequently the clearance under the elbow. Vessel supporting arrangement - Vessels are supported by the following methods Lug supported - Small vessels Skirt Supported with foundation on grade - most preferred Ring girder supported - On table top ( when bottom nozzle needs to be accessed ) Skirt supported - On table top The choice of support may fix the drum elevation for some layouts
Nozzle orientation The following documents are required for orienting the nozzles. 1. Process vessel sketch 2. Level co-ordination diagram 3. P&ID 4. Plant layout specification 5. Nozzle summary 6. Insulation requirements 7. Plot plan
General considerations for locating nozzles
Generally, the following nozzles are present on all drums. 1. Product Inlet 2. Product Outlet 3. Vapour Outlet 4. Vent 5. Drain 6. Instrument Nozzles 7. Steam Out Nozzle 8. Access Manway Orienting the nozzles While orienting these nozzles the following points are to be considered. a) Feed inlet to be placed on any orientation as there are no internals restricting the angle of orientation.The best location will be such that the piping from the nozzle is flexible enough and has the simplest routing. b) Vapour outlet , PSV connections and Vent will be on the top head of the drum. Vapour outlet is best located on the center of the head , though it may have to be shifted based on some layout considerations as explained. A large diameter makes location of the vapour nozzle critical. The nozzle may have to be offset from the center of the drum so that , after two elbows, the piping travels down the drum at a practically supportable distance from the drum. c) Product Outlet will be on the bottom head , best located on the center of the head .This is of goose neck type for vessels with skirt type support and the nozzle flange has to be brought out skirt . d) Level Instrument nozzles should be in the same sector as the inlet nozzle to avoid effects of turbulence. When baffles are provided this consideration is relaxed. e) Pressure tapping for vapour pressure to be on the top of the drum , near the Vapour outlet. f) Temperature tapping for liquid temperature to be in the lower liquid region. It is to be ensured that sufficient space is available for removal o f the temperature element . When multiple temperature elements are required , they are best placed at the same orientation but different elevations . g) Steam out connection should preferably be hill side type on the cylindrical shell so that swirling action is generated inside the vessel. This will ensure faster steam out of the drum.These should be placed as close to the bottom tan line as possible. h) Drain to be located at the lowest point , preferably on the bottom nozzle of the drum. i) Inaccessible Instrument nozzles to be oriented near ladders ( location of ladder and Instrument nozzles to be decided concurrently ) j) Access manway can be located at the following places , depending on the type of access required into the drum. 1) On the top of the drum. (In this case the vent can be located on the blind flange of the access manway.)
2) On the cylindrical portion of the drum (radially or hill side) This is the most preferred location . The orientation of manway should be such that the manway faces the maintenance access area. It should be verified that the davit swing area of the manhole cover does not obstruct the movement of maintenance personnel and does not hit any instruments or instrument nozzle connections. The center line of the manhole should be between 600mm to 1000mm (ideally 760mm) from the top of service elevation of the vessel. k) Goose neck nozzle for Vapour outlet should be considered when piping layout is fixed and requires an elbow immediately at the nozzle. This can be flanged type , thus acting as a manway also for big nozzle diameters. Flange type nozzles have the added advantage that their orientation can be changed even after the delivery of the vessel at site.
Nozzle standouts Nozzles on the top of the drum should have their flange a minimum of 180mm and a maximum of 1000mm from the TOG of the access platform. Nozzle standouts on the shell are calculated on the clearance requirement for maintenance access to nuts on the back of the flange. Due consideration is to be given to vessel insulation when calculating the standout. This standout will be confirmed by mechanical so that the nozzle passes the requirements laid down in 3PS- ( -MV001
Preparing the Nozzle Orientation Document This document should show the plan , and if required , the elevation of the vessel with the location of nozzles on the same. Nozzle orientation is to be from plant north and taken clockwise . Dimensioning should show the radial distance of the vessel flange from the vessel center. A nozzle summary table indicating the Nozzle number,service, size, rating ,flange face, elevation from bottom tan line, and standout from vessel center is to be included in the drawing. For nozzles on the vessel heads , the F/F standout from the bottom or top tan line should be given. .in lieu of elevation from bottom tan line. Miscellaneous Data to be included in Nozzle Orientation Document Lifting Lugs Generally drums can be lifted with two lugs welded below the top tan line . A tailing lug is to be provided near the bottom of the skirt for tailing operation .The preferred locations should be marked on the nozzle orientation drawing .
Earthing Lugs Two earthing lugs , ideally 180( apart should be provided on the lower portion of the skirt. The same should be marked on the nozzle orientation drawing. Name Plate Name plate should be located at a prominent location and marked on the nozzle orientation drawing. Care should be taken that the name plate projects outside the vessel insulation. Vessel Insulation Clips Indicate that insulation clips/rods are required for holding the vessel insulating bands.
Platforms and Access Ladders Platforms are required for the following purposes 1. Operational access to valves and instruments etc. 2. Maintenance access to manways. 3. Mid landings ( when elevation difference between two platforms exceeds 9m ) Calculating the TOG elevation
Platform on the top head of the drum TOG elevation from top of drum head = Insulation thickness + 50mm clearance + Platform member depth(assume 200mm minimum) + 30mm grating. Round off to the next higher multiple of 10.
Platforms on the cylindrical portion of the drum Nozzles - Platform to be 500mm (minimum) below the bottom of flange of nozzle. Instruments (LT/LG) and their standpipes - Platform to be 200mm b elow the lowest process drain on any of these items. Access manways - Platform is to be ideally760mm below the centerline of the manhole. Acceptable range is 600mm to 1500mm below the centerline of the manhole . Mid landing platforms-These are to be provided when the elevation difference between two platforms levels exceeds 9m. The mid landing to be ideally evenly placed between the two platforms. Two platforms being serviced by a single ladder should ideally have an elevation difference of 600mm between them. The platform elevations (TOG ) should be rounded off to the nearest multiple of 10 .
Platform sizing Platform on the top head of the drum This platform should be rectangular .It should cov er all the nozzles ,instruments davits etc. that need access for operations and maintenance. Ideally a space of 750mm should be provided around 3 sides of a nozzle. This may be lowered at the discretion of the piping lead . Side entry access to the platform should be the first preference when deciding the exact shape of the platform. This may be achieved by orienting the platform axis along the ladder orientation and providing an extended landing point . Platforms on the cylindrical portion of the drum Determining the Orientation angles This platform should be circular .Its orientation extent should cover all the nozzles ,instruments davits etc. that need access for operations and maintenance. Platform should extend beyond the centerline of manhole by a minimum of 1 manhole diameter. A free landing space of 750mm is to be provided for access ladders. Ideally a space of 750mm should be provided around the sides of a nozzle. This may however be lowered to 600mm on the discretion of the piping lead . Determining the width The inner radius of the platform should clear the drum insulation by 50mm. Platform width is dictated by operator access requirements.The following considerations are to be taken care of when deciding the width. Minimum platform width is to be 750mm(free of all obstructions). Width of manhole platform is to be minimum 900mm. Platforms may be locally extended width wise at regions where vertical pipes pierce the platform , maintaining 750mm clear space from insulation of piping to handrail of platform. When controls are located on the platform ,the width of the platform is to be 900mm plus the width of the controls.
Platform bracket orientation Platform support brackets are to be oriented so that they clear the vertical piping traveling down the drum , thru the platform. Support bracings for platforms at all elevations should be maintained the same as far as possible. Access ladder
Access ladders are to be vertical. They should have a clear climbing space of 680mm.Toe clearance from the centerline of ladder rung to any obstruction to be 230mm.Special care is to be taken for vessel stiffeners. Cage is to be provided for all ladders at elevation of 2300mm and above.Side entry ladders are the first preference. The ladder is to be oriented so that it can also be utilized for access to instrument connections that are inaccessible from working level. Preparing the Platform Input Document Platform and Access ladder input is transmitted to Civil via a platform input drawing. Platform on the top head of the drum This should clearly indicate the TOG elevation from bottom T/L, dimensions of platform , and its location w.r.t. the vessel center-lines. Grating cutout requirements (indicating size , shape and location) , required swing direction of self closing gate , and davit location need to be marked on the same drawing . Any pipe supports intended to be taken from the platform should be marked. Platforms on the cylindrical portion of the drum This should clearly indicate the TOG elevation from bottom T/L, dimensions of platform (orientation angles and width ), and its outer radius form the vessel axis. Grating cutout requirements (indicating size , shape and orientation) , required swing direction of self closing gate . Any pipe supports intended to be taken from the platform should be marked. Orientations of access ladders should be marked on the respective platform elevation plans. Orienting piping on the face of the column It is imperative that the orientations and standouts of various p iping traveling down the face of the column are calculated keeping in mind the following points Large diameter drums The piping of these drums can travel down the drum radially, with independent supports. Clear minimum space between pipe and shell is to be 300mm excluding any insulation. The pipe with insulation should clear the stiffening ring and its insulation. Minimum orientation angle between two adjacent pipes should be calculated as shown in figure ...( Support points of adjacent piping should be offset to save space between them. as the support brackets will have to be oriented so that there is no clash between the cleats of the supports, or between the support members and bracings.
Small diameter drums Small diameter columns have an inherent problem of supporting and guiding each line independently due to the small circumference available for the piping. After the first rest support near the nozzle , the pipes should be as though the are traveling down a vertical pipe rack . Clear minimum space between back of pipe or shoe and shell is to be 600mm. On the vertical run, minimum spacing requirements have to be followed. Supporting Piping from Drums Piping should be supported form the vessel or its platform when it is difficult to construct a civil support from grade or adjacent structure at the required location. Vessel support may also be taken to take advantage of lower differential thermal growth between vessel and piping , as compared to piping and civil support. Judicious selection of support location can eliminate the requirement of springs. Thumb rules for supporting piping from drums Small loads can be transferred directly to the platform members. These include rest , one way stop , two way stop or hold down supports and the piping layout should be done accordingly. Large loads should be transferred to the vessel shell and the piping layout should be done such that the platform members do not interfere with these independent supports. First piping support is a rest support and it should be as close to the equipment nozzle as possible. Second and subsequent supports are guides and they are to be located as per the allowable piping spans available in the tables. For tall drums , another rest support may be needed. This is done by providing a spring support which will take care of the differential expansion of vessel and piping. Piping support should not cause any hindrance to movement of personnel. Vessel growth should be considered to check clash of a piping support with any adjacent piping or structure. For both these cases , information is to be transferred to civil and mechanical for them to adequately design the support members. This is done via support cleat location plan drawing and nozzle cleat load information table. Support cleat location plan drawing indicates the location of the CPS from a Tan Line , its TOS and its orientation. Nozzle cleat load information table indicates the various loads acting at the support location under various conditions.
Types of supports Supports welded to piping Horizontal trunnions welded to pipe take the vertical load of the pipe. They are generally used in pairs , set apart at 180( . Their axis is perpendicular to line drawn from center of column to center of pipe at the location of support. Trunnion lengths should be adequate enough so that their ends project 50mm from outer edge of support bracket member Shoes are provided for guiding purpose and to prevent insulation cladding hitting the support bracket member. Adequate shoe length is to be taken for differential movement of pipe and vessel. Supports welded to vessel Support brackets( non braced and braced ) and Guide brackets( non braced and braced ) are the most common support arrangements for vertical piping. These can be seen under 3PS-PL015 B13 to B and G to
Calculating the minimum dimensions of support members Load bearing supports Trunnions or springs transfer load to these supports. Minimum clear inside dimensions are calculated so that the insulation cladding is 50mm away from the inside of structural member or supp ort plate of spring. Guide supports Bare pipe is guided directly by the guide bracket. Shoes are provided in pairs ,180( apart , for lines with insulation. These can be single pair or double pair depending upon the type of guiding required at that particular location. The guide gap required by stress is to be added to the end to end-to-end dimensions of bare pipe or pipe with shoes. Preparing the CPS Input Document CPS input is transmitted to Civil and Mechanical via a CPS input drawing. A sketch clearly indicating the TOS, dimensions , and the CPS location w.r.t. the vessel centeline needs to be drawn. Any requirement of additional support plates for springs or trunnions are to be indicated. A summary table indicating the CPS number, TOS, stress file number, corresponding node number from the Nozzle cleat load information chart needs to be created. The Nozzle cleat load information chart indicates the various loads acting at the support location under various conditions. It is to be attached along with the CPS input document.
