I am working on an existing line for which I can give you below information:
1) Line is 16” and has cyclic load (varying from ambient [the ambient temperature ranges from 5° to 52°C] to 300°C in a period of 36 hours)
2) The line is cold insulated due to the design temperature of connected vessel (which is -15°C). This really beats me. I don’t know the exact reason for minus design temperature when the cyclic operating temperatures are above ambient.
3) The line had a spring hanger which is deactivated as the beam holding it failed. Now it is feared that the line load is transferred to the connected equipment nozzle and integrity of the line and connected equipment is endangered. The failure of piping or nozzle or leakage may happen on this line.
4) As a temporary solution to relieve the load on the equipment nozzle (prior to shutdown) we intend to:
a. Do stress analysis of the line with spring hanger on a horizontal part of the line at a new place (near the nozzle). The existing spring hanger was on vertical line before this horizontal portion.
b. Select can-type spring hanger as per stress analysis outcome.
c. Put a clamp with saddle on top of cold insulation & cladding on the point mentioned in a. above. (This may give rise to another problem and which is the insulation density at this point. The insulation density (and compressive strength) at support points in the cold insulated systems is higher than other places. We may have to elongate the saddle to distribute the load so that the unit load per area is lesser than the compressive strength of the insulation).
d. Put the new spring hanger (can-type) below the clamped saddle.
e. Depending upon the temperature of the line at the time of installation (We intend to do this activity when the temperature is at its operating maximum that is 300°C), raise the load column of spring hanger below the clamp by its jacking action and stop when the load indicator reaches the “hot load”.
Now questions to you are:
1) What is your opinion on this strategy as I explained above? If you have some previous experience and have better solution please share with us.
2) How much vertical adjustment in the can-type spring hangers can we get? The hot load will be around 4000 kg. The vertical clearance below the line is around 600mm (available for hanger minus the insulation and saddle height).