flare piping design temperature
flare piping design temperature
(OP)
i have a hot compressor discharge relief scenario. the temperature downstream of the psv in flare is 140 degrees c. my flare piping is design temp 110 deg c.
must the flare piping have a design temp suitable for 140 deg c?
thanks.
must the flare piping have a design temp suitable for 140 deg c?
thanks.





RE: flare piping design temperature
RE: flare piping design temperature
temperature for a short duration relief scenario. i dont want to change flare piping unless necessary.
RE: flare piping design temperature
RE: flare piping design temperature
In short, my answer is, "No, not necessarily.".
RE: flare piping design temperature
So, the existing pipe is nominally limited to 110C at XX psig. What is that pressure value? 110C is a very low temperature limit for piping, so I'm guessing that the value of XX is way higher than the actual pressure you'll see in the flare header during this scenario. In other words, it's very unlikely that this pipe will be close to it's internal stress limit when the temperature is 140C.
The more important question is what impact does this have on the pipe design (expansion/contraction)? This is something that's often overlooked, and it's a real risk for flare headers. I'm familiar with a number of flare hdrs which have experienced loss-of-containment failures because of thermal stresses. Plant personnel generally regard the flare header as a garbage can, and they think they can toss anything in without any reason to be concerned. That's not true. One must be cautious about the following combination of events:
- dumping a high flowrate
- at an unusually high or low temperature
- over a long period of time
If those three points apply to the case which we're discussing, then have a pipe stress analysis performed before proceeding. Otherwise, there's probably no problem.
RE: flare piping design temperature
You probably won't melt the flare material or reduce its strenght significantly (unless it is stainless), but flare pipework is notorious for being designed very thin and in service has corrosion defects. Hence don 1980 is totally correct in his assessment and it is expansion and thermal stress that will be your issue. You need to do as as built, latest condition stress analysis if this is a new relief load.
I recall the texaco refinery in milford haven was virtually destroyed some years ago when the main flare header failed due to entrained liquid punching a hole in it and enveloped the plant in a gas cloud which as the report put it "found an ignition source". A flare header needs to work hard to keep it's contents inside it until it burns it and I often feel it is an overlooked critical safety item so please don't take liberties with it.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: flare piping design temperature
Determine your actual material of construction -- what kind of pipe is it? Then look up the temperature/strength table; ASME Sect IID or B31.3 are two good ones. What temperature does this material start loosing strength? If that temperature is higher than 110°C, use the table temp and ignore the 'artificial' 110°.
If the table gives a 'start of derating' temp lower than 110°, hire a Pipe or Pressure Vessel Eng. to evaluate your header. I'll bet a paycheck that your header is just fine, and the 110° rating is unsupported by engineering calculations.
If it didn't get calculated, it is merely opinion. And your opinion is as valid anoyone elses.