February 9, 2008 at 3:34 am #3799
Recenly we have a fire accident on the top of the coke drum.
The fire is caused by the leakage of a flexible anti-foam pipe.
We would like to know the industrial best practice with regard to this issue: Flexible or Fixed pipe for anti-foam piping?
February 9, 2008 at 9:46 am #7054
ExxonMobil’s best practice is to use hard pipe connections for antifoam, but it is essential that the piping be properly designed for thermal expansion, especially as related to coker drum vertical growth and contraction as the coke drum cycles. Key points:
- Connections to piping or equipment (coke drum) should be gusseted to provide extra strength and support at the connection to keep small piping from breaking off
- Connections should also use integrally reinforced connections where possible – no pads
- Can design in “expansion loops” in short runs of pipe to provide flexibility
- Longer runs of small bore pipe tend to be inherently more flexible
- Can support small bore piping off of coke drums and/or larger piping (OH piping), and then provide “guides” vs supports on structure that doesn’t move – i.e. clamp to OH line and then let it float through the floor plate and just rest on guides below the deck. Guides allow it to move freely but still constrained within allowable limits – no overstress.
- Install wear pads where necessary. Since piping moves around quite a bit with coke drums, it can run on structural steel, supports, etc. We have seen wear on the walls of small bore piping that is really bad – almost had a hole through on one Cokers antifoam piping – wear pads help quite a bit.
A secondary option is to use braided hosing. However, an effective Inspection & Preventive Maintenance program must be in place, so that the hose is replaced as needed.
Best regards – Mitch Moloney
February 29, 2008 at 9:38 am #7010
We plan to use fixed pipe as the flexible pipe is prone to leak.
But we do not know how to determine the pipe size, 1″ or 2″ , which is better?
Small pipe is more flexible, but it seem easy to break.
The flow rate of the antifoam in this Delayed Coker plant is 6 m3/h.
It seem 1″ is enough, but we worry that it may break sometime.
March 1, 2008 at 5:07 pm #7006
We typically have 2″ gusseted nozzles on the coke drum, swedged to 1.5″ diameter pipe for the run of carrier and antifoam to each coke drum. You do not need 2″ pipe for the run of carrier oil and antifoam to each coke drum, unless you are injecting a lot of carrier (not recommended). 2″ pipe is less flexible, as well. Still, I cannot overemphasize the need to perform proper process hydraulic calculations and piping flexibility models, that take into account the cold and hot coke drum positions and the cold and warm antifoam piping positions. Best regards – Mitch Moloney
March 14, 2008 at 12:33 pm #6988
In our DCS (we have 2) our antifoam piping are fixed pipe because as you have written: Safety.
We do not have a bend. We replace to removable T. It is easy to clean with steam.
Of course, you need to design the antifoam fixed pipe in order to be “flexible” with the drum movement
The first unit started in 1999 and we do not have a lealing
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