What is Pressure Vessel Clip
The attachments welded to the equipment by the vendor for bolting the brackets for pipe supporting are known as Pressure Vessel clips or Cleats. Fig. 1 shows typical clips for a horizontal pressure vessel. Pressure Vessel clips are used mainly for supporting purposes.
Features of Vessel Clips
Equipment requires hydro/ pneumatic testing at vendors workshop to check leakage possibility and after the testing, no welding is permitted on the equipment as it may require stress relieving, radiography and subsequently re-hydro testing. Also, brackets are not welded directly to the vessel as it is difficult to transport and erect the equipment at the site. So vendors provide clips or cleats in the form of extended attachments from the vessel plate at the required locations specified by the piping team.
Vessel clip information is furnished to the mechanical static equipment department which they forward to the equipment vendor/manufacturer along with nozzle orientation.
The vendor prepares surface development drawing of the vessel and can check the fouling with weld seam and neighboring nozzles or clips.
Vessel Clip Selection Procedure
Refer Fig. 2 for a flow diagram of the Clip selection procedure.
Major Considerations for Clip Loading
The Vessel clip should be able to take the worst load combination possible as per stress analysis criteria.
- Operating load: pipe metal weight +pipe component weight like valve, flanges etc.+ Insulation + fluid + thermal load (at operating/ design conditions).
- Hydrotesting load: clip load during the hydro test ( Without insulation)
- Occasional loads: pipe metal weight + pipe component weight like valve, flange etc.+ Insulation wt.+ Fluid weight+ thermal load at operating (not at design conditions)+ wind/ seismic load.
Few Salient Points
The following points to be kept in mind while providing clip loading information.
- IF A VAPOUR LINE IS TO BE HYDRO TESTED AND IT’S LOAD IS EXCEEDING THE CLIP ALLOWABLES: In that case, the line can be hydro tested (along with column) at the ground and can be erected with the column.
- IF OPERATING LOAD IS GREATER THAN CLIP CAPACITY: Refer Fig. 3
How to Choose the Location of the Vessel Cleat
Follow the below-mentioned steps while selecting the vessel clip location.
- First clip should be load taking support
- As close as possible to the nozzle.
- To reduce the differential expansion between the pipe and the column/ vessel.
- After that guide clip should be provided after the specified span and then based on a guide span for vertical lines guides to be provided.
- There may be high sustained stress at the bend with only one load taking clip support.
- The requirement of second load taking clip should be checked.
- Second load taking clip may require spring supports.
Points to Check while Deciding Vessel Clips
While deciding clip location and load always check the following points
- Load capacity
- Insulation: bare or insulated pipe
- Width of bracket: based on insulation the width of the bracket
- Bracket length limitations
- Fouling: bracket should not foul with adjacent bracket, adjacent pipe, weld joint of elbow, the pad of nozzle
How to Avoid Fouling with Vessel Clip
- By staggering the supports
- By changing the orientation of line
- By choosing the suitable bracket
Fig. 4 shows a typical pipe supported from vessel clips.
Few more Resources for you..
A short Presentation on Basics of Pressure Vessels
Brief Explanation of Major Pressure Vessel Parts
10 points to keep in mind while using project specific pressure vessel nozzle load tables during stress analysis
Understanding Pressure and Temperature in the context of Pressure Vessel Design
A Video tutorial on “Comprehensive Design Code Coverage for Pressure Vessel and Heat Exchanger Design” by Bentley Institute