13 replies to this topic

[go-fish]

Hi

What kind of flow velocity is desirable for refined hydrocarbons in transfer pipelines?

Thanks

[JMW]

There should be an ASTM standard somewhere which will govern the maximum flowrates referenced to static electricty generation.
ASTM D4865 - 09
After that it is about all the usual things, pumping energy/capacity, headloss etc.
In marine fuel bunkering the use of centrifugal pumps and high viscosity fuels means the operation is a compromise between heating the fuel to reduce viscosity enough to get a good flow. But while heating takes energy, the higher lower the temp, the higher the viscosity and the lower the flowrate. This means that turn-around times are longer. So its down to a balance of different operational and economic factors.

Not sure what else you might be thinking of.

Edited by JMW, 10 March 2012 - 04:40 AM.

[Himanshu Sharma]

20 ft/sec Maximum is a general rule of thumb for HC Liquid in KCS lines,but i have seen process engineers generally limiting it to 10 ft/sec.This is related to erosion and Line pipe life considerations.

Alloy steel lines can permit higher up to 30 ft/sec maximum.

Edited by Himanshu Sharma, 12 March 2012 - 09:32 AM.

[J_Leo]

the speed limits are different for liquid , gas and mixed hydrocarbon lines.

For liquid, speed limit is also related to the pipe size. The larger of the pipe, the bigger of the speed limit. For pipe large than 8", the speed limit is 6-12 ft/s, depending on the state of the liquid. For saturated liquid, lower speed is allowed.

For gas, the speed limit is much high. It can be up to 200ft/s and even more. The smaller of the density, the higher of the allowed speet limit. Speed limit is proportional to （density^(-1/2)

[Robert Montoya]

According API RP 14E the maximum velocity is: Vmax (ft/s)= 100/(density lbft3)^1/2

[ankur2061]

go-fish,

The point JMW has made is absolutely right. For refined petroleum products also known as white oil products such as gasoline, jet fuel and kerosene the velocities should be such that a build-up of static electricity is avoided. I had posted a blog on flow rates for loading of white oil products in tankers where velocity guidelines are provided to prevent static electricity build-up while the product is flowing in a pipe. Have a look at the blog entry at:

http://www.cheresour...e-oil-products/

Hope this helps.

Regards,
Ankur.

[go-fish]

Thanks everyone

@ ankur

Do refineries generally add any additives for preventation of static build -up? I am using about 2.2 m3/hr in 24 inch pipe for gasoline. Is it high?

[R NESAMANI]

Thank you all .
We are operating LPG pipeline of 1300 km long. What is the maximum flow velocity? which std? how to calculate the velocity?
Just i want to check whether we operating correctly or not....?

[kkala]

Following useful threads represent past discussions on allowable velocities, as well as static electricity (and antistatic additives) for hydrocarbons.
http://www.cheresour...id-line-sizing/ '> http://www.cheresour...id-line-sizing/ , from post No 6 (by Narmia) on.
http://www.cheresour...rmissible-speed '> http://www.cheresour...rmissible-speed
http://www.cheresour...city-generation '> http://www.cheresour...city-generation .

[ankur2061]

Thanks everyone

@ ankur

Do refineries generally add any additives for preventation of static build -up? I am using about 2.2 m3/hr in 24 inch pipe for gasoline. Is it high?

go-fish,

Refineries do add additives for prevention of static build-up. The additive type is dependent on the product and its resistivity or the static build-up. Anti-static additive suppliers can provide you the dosage rate for their chemical and the refinery product for which it can b used.

Some general design guidelines for he design of additives of any type are provided below:

- toxicity;
- chemical and thermal stability (including shelf life of the additive)
- viscosity;
- compatibility with additive system materials (e.g. elastomers).

Very toxic additives require gas-tight designs, pump seals and special precautions for their transfer. The pump seals should be compatible with the type of additives to be used.

Thermal stability properties will dictate the requirements for temperature alarming, safety relief valves and the use of special injection systems such as eductor systems.

The different characteristics of each type additive may require specific design and operating guidelines.

Hope this helps.

Regards,
Ankur.

Edited by ankur2061, 20 March 2012 - 10:29 AM.

[kkala]

As indicated in last link of post No 9 (by kkala) main factor to determine use of antistatic additives is (specific) electrical conductivity of the fuel handled (usual units pS/m). Small electrical conductivities increase the risk due to static electricity. And electrical conductivity tends to decrease by lowering sulfur content of a fuel (rather a trend nowadays).
Wikipedia is generally reported in said link, but the specific article is http://en.wikipedia...ic_electricity , paragraph "Static built-up in flowing flammable and ignitable materials" and "Fueling operations". The article is judged quite useful for introduction, yet following point seems to need further treatment.
Wikipedia: "Because water content has a large impact on the fluids dielectric constant, the recommended velocity for hydrocarbon fluids containing water should be limited to 1 meter per second".
Comment:Velocity limit of 1 m/s (low velocity) is applicable wherever there is possibility of contacting air (e.g. at end of pipe discharging into a cone roof atmospheric tank). This is a legal requirement in several countries for all hydrocarbon liquids (fuels), irrespectively of their water content.
Low velocity should be also maintained upstream of potential air contact (e.g. said end of pipe) at a length corresponding to 5 times the relaxation time of the fuel (see wikipedia article). This can dictate increase of pipeline diameter in this last pipe part.
In the rest pipe, velocity can be higher than 1 m/s and comply with the relevant pipe sizing criteria (links of post No 9). There is no air at that part of pipe, so an electric discharge (if any) will not cause fire or explosion. Of course bonding cables and earthing have to be applied on the pipeline (see wikipedia). Look at http://epa.gov/regio...ing_venting.pdf '> http://epa.gov/regio...ing_venting.pdf for explanations on bonding.
For quite low fuel conductivities (lower than about 10 pS/m, per wikipedia) above measures (low velocity, bonding, earthing) are not safe enough. Then antistatic additives are recommended, presumably in addition, after a specific survey.
It is noted that water conductivity is higher than than of liquid hydrocarbons, more than 10E6 pS/m (wikipedia article), so water addition rather increases fuel conductivity globally.
As mentioned, advise / opinion/ supplements on the above would be appreciated, to make this safety point clear.

[ankur2061]

go-fish,

For further details on anti-static additives refer the liks below:

http://books.google....asoline&f=false

http://en.wikipedia....ntistatic_agent

Regards,
Ankur.

[JMW]

From a thread in another forum it has been pointed out that aviation fuels usually also have an antistatic additive added but it was also pointed out that these additives are shear sensitive and breakdown rapidly so are only added prior to critical operations such as fuelling aircraft.
I don't know enough here to comment but wonder if similar considerations are relevant to other antistatic components.

[psuche03]

I see this thread is a bit old at this point, but I can add a few good references.  API RP 2003 (protection against ignitions - static-lightening-stray currents) gives specific velocities to limit for static charge build up.  Additionally, the ISGOTT (International Safety Guidelines for Oil Tankers and Terminals) give velocity limits for loading ships.  Both documents indicate the same velocity limits.  Also see the section on charge dissipation time when passing through a filter.  Any engineer should review the document, so I'll refrain from listing the specific velocity limits.