IPE-TM-300 Vessels
Small Vessels Design
IPE-TM-300-16
1. Table of Contents
1. Table of Contents 1
2. Purpose 1
3. General 2
4. Manways 2
4.1 Vessels greater than or equal to 48” (1200) ID 2
Figure 1A 2
4.2 Vessels less than 48” (1200) ID and greater than or equal to 36” (900) ID 3
Figure 1B 3
4.3 Vessel less than 36” (900) ID and greater than or equal to 30” (750) ID 3
Figure 1C 3
4.4 Vessels less than 30” (750) ID 3
Figure 1D 3
5. Head Types 4
5.1 Vessels greater than or equal to 36” (900) ID 4
5.2 Vessels less than 36” (900) ID 4
6. Body Flanges 4
6.1 Vessels greater than or equal to 30” (750) ID 5
6.2 Vessels less than 30” (750) ID 5
Figure 2 5
7. Inlet Piping 5
7.1 Vessels greater than or equal to 30” (750) ID 6
7.2 Vessels less than 30” (750) ID. 6
Figure 3 6
8. Non-Accessible Internals 7
Figure 4 7
9. Packing 7
Figure 5 8
10. Cartridge Trays 8
Figure 6 9
11. Summary Forms 10
12. References 10
13. Metric Dimensions 11
14. Manway/Handhole Table 11
Layouts and details for sieve, valve and bubble cap trays and packing distributors, retainers and supports are not covered in these guidelines.
2. Purpose
This procedure provides guidelines for determining the dimensions and requirements used in the design of small vessels. Small vessels are considered to be any vessel less than 4’-0” (1200) in diameter.
3. General
Use this information to complete the design of small diameter vessels. This includes using P254 and any hand calculation sheets or procedures.
This procedure provides typical design standards for small vessels. Alternate designs are possible after consultation with the process/technology specialist and/or the vessel specialist.
4. Manways
Columns having an ID of 48” (1200) or larger should apply the Inflection Point Engineering standard manway size of 24” ID. Manways larger than 24” ID may be used to accommodate entry of large internals.
Items 4.2 through 4.4 should be discussed and resolved with the customer prior to performing any design work on the vessel.
4.1 Vessels greater than or equal to 48” (1200) ID
a. The standard manway is 24” ID. Vessels having large internals may require a manway diameter greater than 24” ID.
b. The top manway is normally located on the side of the vessel. Horizontal vessels typically have the manway located on the side of the shell.
Figure 1A
c. When MD Trays are specified, the top manway shall always be on the vessel side. This makes the insertion of the trays and internals easier.
4.2 Vessels less than 48” (1200) ID and greater than or equal to 36” (900) ID
a. Typically, use a manway having an 18” ID.
b. Manways greater than 18” ID may only be used after consultation with the customer and the Inflection Point Engineering technology specialist.
c. If a manway greater than 50% of the vessel ID is required, the design engineer should consider providing a flanged head (curved or flat). Body flanges on the vessel may also be considered.
Figure 1B
4.3 Vessel less than 36” (900) ID and greater than or equal to 30” (750) ID
a. Provide a flanged head (curved or flat)
b. Manways (if required) shall be 18” ID
Figure 1C
4.4 Vessels less than 30” (750) ID
Figure 1D
a. The design engineer should provide a flanged head (curved or flat) on the vessel.
b. Handholes (6” – 12”) may be applied to be used as inspection ports. The maximum handhole size should be limited to 50% of the vessel ID. Two handholes should be provided; one handhole can be used for a lighting source while the other is used for access to the vessel interior. See the Handhole table in Section 14.
c. Body flanges are used as required to provide access to internals..
5. Head Types
Generally Inflection Point Engineering applies 2:1 elliptical heads to all vessel designs under 1000 psig (70.0 kg/cm2g) design pressure.
5.1 Vessels greater than or equal to 36” (900) ID
See Figures 1A and 1B above.
a. Normally use 2:1 elliptical heads.
b. Hemispherical heads may be used for applications over 1000 psig (70.0 kg/cm2g) design pressure.
5.2 Vessels less than 36” (900) ID
See Figures 1C and 1D above
Specify a flanged head to provide access to the vessel interior. The flanged head may be curved (typically 2:1 elliptical) or flat. Flat heads are usually limited to applications requiring CL RF150# flanges. Vessel designs requiring higher flange classes should use a flanged curved head (typically 2:1 elliptical) .
6. Body Flanges
Body flanges are applied to vessel designs to provide access for the installation, removal, repair and maintenance of internals. Generally vessels having an ID greater than or equal to 30” (750) do not require body flanges. Adequate access to internals on these vessels can usually be provided via manways.
Body flanges can be difficult to seal due to the large surface area associated with the flange. Every body flange that is installed is an additional point for leakage to occur. Therefore the application of body flanges should be kept to a minimum.
6.1 Vessels greater than or equal to 30” (750) ID
a. Typically body flanges are not used used when the vessel ID is 30” (750) or greater, except for very specialized applications.
b. Consult with the technology specialist to determine if body flanges are required.
6.2 Vessels less than 30” (750) ID
a. Use body flanges as needed to provide access to vessel internals.
b. Usually the maximum working access reach into a vessel is 24” (600) from the face of the body flange, without the use of special tools or procedures.
c. Where possible, the design engineer should locate internals that require working access such that they are no more than 24” (600) from the face of the nearest body flange.
Figure 2
d. Working access reach greater than 24” (600) will usually require special tools to accomplish maintenance or repair. If possible, relocate internals to avoid special tools requirement.
e. If no other solution for accessing internals is possible, provide additional body flanges
f. When body flanges are specified, include the following note on the 301 specification: “Contractor to verify the number and location of body flanges after consulting with the internals supplier.” This note should be applied to each body flanges on the vessel specification.
7. Inlet Piping
Small vessels may require stab-in inlet piping arrangements. This occurs when cartridge trays or other internals that require full diameter clearance for installation (mesh blankets, hold down screens, etc.) are provided in the vessel design. Cartridge trays, mesh blanket or other internals must be installed before the stab-in inlet piping to avoid mechanical interference.
The application of stab-in inlet piping is limited to vessels that are too small to allow personnel to enter the vessel and work effectively. Inflection Point Engineering represents that a man can enter and work in a vessel as small as 30” (750) ID.
7.1 Vessels greater than or equal to 30” (750) ID
In general, stab-in inlet piping should not be used for vessel designs having a diameter of 30” (750) or greater.
7.2 Vessels less than 30” (750) ID.
a. The inlet pipe normally needs to be removable to allow inspection, cleaning or replacement. This is provided in larger columns by an internal flange. However, internal flanges do not provide enough access in small columns.
Stab-in inlet piping requires a nozzle ID that is large enough to allow the largest stab-in inlet piping fitting to pass through. Example: a 1½” Sch. 40 inlet pipe has an OD of 1.90”. The smallest nozzle that can pass the 1½” inlet piping is 2” Sch. 80, which has an ID of 1.939”. See IPE-TM-300-03, “Minimum Openings Required for Passage of Pipe fittings”.
Figure 3
b. If the stab-in inlet piping has a fitting on the end (tee or elbow), the required nozzle size will be significantly larger than the OD of the stab-in inlet piping. In the example above, if the 1-½” inlet piping has a tee at the end of it, the required nozzle size to allow the 1-½” tee pass through is a 6” Sch. 40 nozzle. See IPE-TM-300-03, “Minimum Openings Required for Passage of Pipe fittings”.
c. Provide a note for each occurrence of items “A” and “B” above stating “Contractor to confirm stab-in inlet piping & fittings will pass through the vessel inlet nozzle”.
d. Avoid the use of elbows on the stab-in inlet distributor that are turned downward. The velocity of material exiting the elbow can disturb the liquid below the outlet, generating additional liquid entrained in the vapor.
8. Non-Accessible Internals
Welded items such as vortex breakers and some baffles are attached to the vessel during fabrication of the vessel. Generally access to these types of internals isn’t required. Inspection ports for the bottom of the vessel are normally provided if personnel access is not feasible.
Figure 4
9. Packing
9.1 Packing is frequently used in small diameter columns instead of trays for the following reasons:
- Ease of loading
- Access required only at feed points
- Potential lower cost than cartridge trays
9.2 There are some guidelines that the designer should be aware of when developing a column design using packing. These guidelines are based on recommendations made by FRI in their Design Practice 3.07 called “Design of Small Scale Columns”.
- The maximum ratio of Vessel ID to packed bed depth should be no more than 10/1.
- The maximum number of theoretical stages should be 10-12 per bed.
- The minimum ratio of vessel ID to the largest packing dimension should be at least 10. This item limits the packing size, based on the vessel ID.
Packed beds have a tendency to mal-distribute by collecting liquid at the vessel walls. The items listed in 9.2 limit the mal-distribution by requiring long beds to be separated into multiple beds. Multiple beds require a liquid collector/re-distributor arrangement between the beds. The collector/re-distributor ensures the liquid is evenly distributed onto the subsequent packed bed.
Figure 5
10. Cartridge Trays
Cartridge trays are used for some small diameter columns. Packing is usually preferred over cartridge trays, due to its ease of loading and minimal use of body flanges.
However there are some applications where cartridge trays are more advantageous than packing. Some of these applications are:
- Fouling systems
- Some foaming systems
- High pressure systems
- Systems requiring large turndown
The designer should consider the following design points when specifying cartridge trays.
- Each bundle of cartridge trays should be limited to a maximum of 8-10 trays per bundle. This will ensure that the friction of the cartridge tray against the vessel wall is not excessive, which could damage the cartridges or prevent complete insertion into the vessel.
Figure 6
- Ensure that adequate access to the vessel interior is provided with inspection nozzles and body flanges.
- Stab-in inlet piping may be required to allow the cartridges to pass the feed point.
- Typical access points are at feed and reflux nozzles, the top of every cartridge bundle. Access may also be required at the bottom of every bundle to inspect/maintain the cartridge support clips.
- The vessel shell may have to be fabricated with a special roundness tolerance (smaller tolerance than code) to ensure the cartridge bundle can be fully inserted into the vessel without binding or damaging the bundle. Add a note to the 301 specification stating “Contractor to confirm vessel roundness tolerance after consultation with tray vendor”.
11. Summary Forms
The following Forms contain the basis for determining and the space for recording the necessary information for the subject internals. Access these forms using the Intranet database.
| Form No. | Title |
|---|---|
| Form ” | Form ” |
| Form ” | Form ” |
| Form ” | Form ” |
| Form | Form |
| Form ” | Form ” |
12. References
Consult the following Documentation System Procedures, Inflection Point Engineering Standard Specification and Standard Drawings for additional information.
| Document No. | Title |
|---|---|
| Procedure IPE-TM-300-01 | Metric Equivalents for Vessels and Trays |
| Procedure IPE-TM-300-02 | Vessel Level Instrument and Level Indicator Installation |
| Procedure IPE-TM-300-03 | Vessel Nozzles, Internals and Ancillaries |
| Procedure PSD-18 | Project Specification 301 Preparation |
| Standard Specification 3-18 | Trays and Packing (Random and Structured) |
| Standard Drawings 3-192 to 250, 3-400 to 417 | Distributor Traps |
| Standard Drawings 3-270 to 273 | Stabbed in Reboiler Tubes |
| Standard Drawing 3-274 | Drawoff Wells for Reboilers |
| Standard Drawings 3-290 to 298 | Partial Drawoff Accumulator Trays |
| Standard Drawing 3-288 | Total Drawoff Accumulator Trays |
| Standard Drawings 3-340 to 352 | Collector Trays |
| Standard Drawings 3-282, 284 | Blind Trays |
| Standard Drawing 3-280 | Traps |
| Standard Drawing 3-252 | Disc and Donut Pans |
| Standard Drawings 3-254 to 262 | Side to Side Pan |
13. Metric Dimensions
This procedure assumes that the required values are determined by using English units. When the required values are to be in metric units, convert the English units to metric using the guidelines in Procedure .
14. Manway/Handhole Table
The table provided below indicates the maximum manway size that should be applied to vessel designs. Note that vessels over 48” may have large manways applied, up to 50% of the vessel diameter. Nozzle diameters less than 18” ID are used as inspection ports.
| Diameter Basis | Vessel ID | Vessel ID | Vessel ID | Vessel ID | Nominal Pipe Size | Nominal Pipe Size | Nominal Pipe Size | Nominal Pipe Size | Nominal Pipe Size | Nominal Pipe Size | Nominal Pipe Size |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Vessel Diameter | 48” | 42” | 36” | 30” | 24” | 20” | 18” | 16” | 14” | 12” | <=10” |
| Nozzle Diameter | 24” ID | 18” ID | 18” ID | 18” ID | 12” | 10” | 8” | 8” | 6” | 6” | none |
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