hot oil coil 1

[Faster7]

what is best practice to test a leak suspected hot oil coils for crude storage Buffer tank?.
the coils pipe is A106 Gr B NPS 3" seamless pipes, used to heat up tank store heavy crude oil with 450,000 barrels 80 diameter, 15M maximum liquid height.
the tank have 3 coils (loops) supplied from 6 inch main header.
- heating media is therminol55.
- operating pressure 9 bar, maximum temperature 250 deg.C.
- the heating system is a loop from horizontal vessel to heater, to tank coils and back.
- the coils is welded joints which changed from flanged joints after last internal inspection.
- the last internal inspection is before 5 years.
- we test every coil and monitor vessel level suspected in 2 coils and isolated ,
- the tank is in-service now and will not going to make internal inspection soon.
- suspect of leak because of noticed decrease in level of heating medium in hot oil horizontal vessel.
- Crude is sweet not corrosive.
but we need to confirm that
is pressure test with therminol ok? and what pressure we need to use is it MOP or design pressure?.
and what hold time we have to use is 24 hours or 4 hours?


Regards

 

[LittleInch]

Leak test is usually 1.1 x MOP.

If you haven't noticed a leak / drop in pressure in 4 hours then it's too small to worry about.

But allow plenty of time for thermal equalisation( 3-4 hours) before the main test.

but there are many causes of less heating - fouling of the tubes / coking / scaling being the main one.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Faster7]

thank you LittlenInch always have valuable inputs.

 

[LittleInch]

Sorry, I misread your post and if, as you say the level in the heating MEDIUM tank is going down then looks like a leak somewhere. Therminol doesn't exactly evaporate....

I thought you said heating...

If the tubes were flanged and now welded maybe they have got overstressedof if they just cut the flanges off and then welded the ends together? Plus did they cut the pipe back to get rid of the HAZ?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Faster7]

yes probably we suspected in welding cracks. yes they must cut weld and HAZ put frankly i am not sure they did or not.