6 replies to this topic

[go-fish]

Normally, I have seen that the max. design temperature of a storage vessel is dependent on max. ambient temperature, solar input, max. product rundown temperature. However, if for a fire case, the relieving temperature of a PRV on the vessel is highest of all, does that mean the design temperature of the vessel should be the boiling temperature of the tank content at the relieving pressure.

[ankur2061]

go-fish,

Design temperature (DT) for a vessel is not based on relieving temperature conditions during a fire. Fire Relief is an emergency condition for any vessel and I have never encountered the vessel design temperature based on fire relief conditions.

DT for a vessel would be based on a margin over the maximum operating temperature (MOT). The margin I am talking about is based on judgement about the operating conditions the vessel is subjected to, including operating conditions when the process is upset. The margin could be also based upon pre-defined guidelines for a particular type of process or based on guidelines that a company has adopted over the maximum operating temperature.

Hope this helps.

Regards,
Ankur.

[Root]

go-Fish,
A very good discussion you can find on this topic from http://www.eng-tips.....cfm?qid=209974
Hope this will help you for DT philosophy.
Good luck
Toor

[go-fish]

Ankur and Toor

Many Thanks. I think I was being over conservative.

[knapee]

Is Design temperature also refer to the mean metal temperature ?

The mean metal temperature in the component under consideration at the most severe condition of coincident pressure, liquid level (including fluidized or bulk solids), and vessel pressure drop expected during operation. More than one set of design conditions should be specified if the most severe pressure, temperature, liquid level, and vessel pressure drop will not occur at the same time.

This is usually, but not necessarily, the warmest temperature for equipment with only one set of design
conditions

Edited by knapee, 07 April 2012 - 06:02 AM.

[fallah]

go-fish,

The exceptional temperature created by fire will not be considered in DT evaluation for tanks/vessels. Indeed, for such storage tanks due to very low design pressure, normally emergency vents would cover the fire case relief not a PRV.

Fallah

[knapee]

Design Temperature 120F and below
1.,Brittle Fracture is a problem.
2. Process design should be setting Minimum temp.
3.where min. operating temp are above ambient, in warm climates use lowest one day mean temperature.

Design Temperate above 120F to 650F (stress for C.S. are constant)
1. 50F normally added to operating temperature to get design temperature
2. 650~850F. Use very minimum increment for c.s. because allowable stress decrease
with increasing temp.
3. 850F above, Minimum temp should be added.
4. Design metal temperature for internally insulated vessels is normally set at 650F for fluid temperature above 650F
5. Equipment subject to steam out should be designed for steam temperature.
6. Consider effect of cooling water failure, reflux pump failure, etc.

Materials for low temperature service.
1. down to -20F use steel that meets proper impact requirements
2. Form -20 F to -50 F use fully killed and Fine grained steels.