Re: Fire Case

It has always been my understanding that analysis of piping/equipment at risk due to fire exposure pertains to its protection against excessive over-pressure. Therefore analysis pertains not so much with the resulting pipe stress but rather the protection of vessel/pipe/tanks based on credible overpressure scenarios using API 520/521 standards. In case of a gas-filled pressure equipment such as process piping in which the credible overpressure  scenarios is due to external fire – treatment is a bit different, perhaps ASME Code Case 2211-1 may provide some understanding. The focus should be risk reduction in any external fire case scenarios or prevention of failure using the result of process hazard analysis.

• In PipingDesign@yahoogroups.com, "Tushar Rajyaguru" <trajyagu@l...> wrote:
  >
  > The discussion is getting really interesting. I would further
  clear some points.
  >
  > 1) Analysis Temperature : Let me clarify this exercise may be
  carried out only for the cases where there is significant difference in operating and design conditions. There is no thumb rules, no written guidelines. Purely engineering judgement and common sense.
  >
  > With higher temperature you will end up with large gaps or else,
  increase the support loads (if higher frequency is to be maintained) and design heavy supports. This one is cost implication. This support may not be active in very low operating cases and sometimes very purpose of analysis is killed. Intension is not to simply analyse the line in operating cases , but to arrive at some justifiable and logical temp. which may actually be there in worst situations.
  >
  > I can give you some practical examples. In one of project flare
  design temperature is 350 deg. C. while operating temp. was around 70. We just inquired from where this magic figure of 350 came ? The process philosophy is design temp should be considered as temp. of max. temp. tapping coming to flare. Moreover fire case etc. was also considered. Now my logic is out of say 100 tapings, 90 tapings are below 100 deg c and only due to 2-3 tapings of high temp. is it wise to design entire flare header as well as all connected tapings for this temperature ? In such cases each tapping shall be reviewed and with help of process people you can arrive at some lower temp. For header it is difficult to determine the exact gradient, so we can vary temp. according to design temp. of tapping from one tapping to next tapping and make some temp. zones.
  >
  > Now let us come to fire case. The purpose of fire case is see that
  piping material should withstand some minimum temperature in case of fire and not to see that when fire is on, plant should run normally and all support as well as nozzles are safe. In case of fire, plant will be immediately shut down and there is no point in analysing such hypothetical conditions.
  >
  > Another interesting case is analysis of reciprocating compressor
  lines. the design temp. of suction line was around 180 deg while operating just 40 deg. The minimum frequency to be maintained is 23 Hz. Just imagine, you need to hold each and every corner to reach this frequency in operating case. And, think what would be result in design case ? If you want to satisfy both conditions, just provide loops everywhere and kill the piping. The logic of such a high dgn temp. was spill back from discharge line to the suction line whose dgn temp. was 180. Now if suction itself comes at 180, discharge will reach beyond 250 and there is high temp. trip of 160 deg. in discharge line. so there is no possibility of suction temp. can reach beyond 70 as per our calculations. So analysis temp .can be set as 70 for suction line.
  >
  > Conclusion, apply your mind, engineering is not all about rules,
  regulations and bid requirements. We should use our own engineering judgement and common sense. If you are true technically bid itself can be changed.
  >
  > ================================================
  > "NO EFFORT IN LIFE GOES UNPAID, HENCE GO AHEAD"
  > ================================================
  > Tushar K. Rajyaguru
  > Plant & Piping Engineering,
  > Larsen & Toubro - Chiyoda Ltd.,
  >
  >
  >
  > [Non-text portions of this message have been removed]