There is no one simple answer to this question ...
Steam out is a procedure used to THERMALLY clean out a system.
It is important to consider both the maximum temperature that will be acceptable for cleaning and the pressure consequences of an full open valve. Use of HP steam may overpressurize and damage equipment.
Additionally, when the steam condenses, there may be a vacuum condition that the equipment was not designed for. I personally have been involved with many thinned wall components that have been ruined by vacuum due to inexperienced engineers like you ....
What are the temperatures and pressures of your LP/MP/HP steam ?
The connection of the steam pipe may be based on the steam-out temperature as required for the operation.
As MJC mentioned, you may make sure the P & T of your LP/MP/HP steam, and use the proper one for the service.
And in another project;
LP: 8 kg, 225C.
HP: 40 kg, 385C.
(No MP)
I saw the first case using MP steam for steam-out & flushing condition. Second case using LP steam for the same.
I am getting why they are used for these two projects from MJC's answer.
But if you can give me a tentative pressure/temperature boundary to chose that would be helpful.
Additional information: Both were coker plants in hot sites, so there is no scope of having negative temperature except probably in the Debutanizer section due to auto-refrigeration.
What can MP or HP steam do, that LP steam cannot? If there is no particular reason to steam out the facility at higher temperatures corresponding to MP/HP steam, then LP steam is your choice.
