16 replies to this topic

[colt16]

Anyone with Marine Loading Arm design experience can comment on what should be the velocity limit for the specification of these equipment?

 

Seems like OCIMF standard has two criteria - 12.0m/s to prevent vibration in Marine Loading Arm and less than 7.0 m/s to prevent static electricity accumulation in refined petroleum products. 

 

My question - is the 7.0m/s too conservative? Even OCIMF say that it may be too low in their ISGOTT publication.

[ankur2061]

Have a look at the following:

 

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

 

Regards,

Ankur.

[colt16]

Have a look at the following:

 

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

 

Regards,

Ankur.

 

Sorry sir but the above link doesn't understand the query that I posed. It seems that the charts provided is more conservative than OCIMF standard for 11.0m/s but it doesn't answer the question from static electricity generation point of view.

[ankur2061]

Static electricity generation is a function of the conductance of electric charge by the product being handled. Many a times anti-static additives are added to white petroleum products to increase conductance and prevent accumulation of static charge

 

Have a look at the following link in terms of restricting loading rates to prevent static charge generation:

 

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

 

Regards,

Ankur.

[colt16]

Static electricity generation is a function of the conductance of electric charge by the product being handled. Many a times anti-static additives are added to white petroleum products to increase conductance and prevent accumulation of static charge

 

Have a look at the following link in terms of restricting loading rates to prevent static charge generation:

 

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

 

Regards,

Ankur.

 

these refer to bulk road vehicles. are you sure they are the same for marine loading arms?

 

although I appreciate the links, I already know many of the things you posted. I was hoping someone with the familiarity of working with OCIMF standards can shed some light. thanks.

Edited by tanykiat, 14 January 2015 - 04:44 AM.

[ankur2061]

Static charge due to high flow velocity has nothing to do with road tanker or marine loading. The guidelines in the blog entry are specific to keeping the product of velocity and pipe internal diameter within certain limits for preventing accumulation of static charge. In the blog entry, it clearly sates that if the conductivity is less thea 50 pS/m or unknown and sulfur content less than 50 mg/kg (ppmw), the product of velocity and pipe internal diameter should not exceed 0.5 m2/s.

 

Assuming that you don't know the conductivity of the fluid being loaded and also the sulfur content, you still have a conservative lower flow rate for prevention of static charge buildup considering a value of 0.5 m2/s.

 

Regards,

Ankur.

[colt16]

Static charge due to high flow velocity has nothing to do with road tanker or marine loading. The guidelines in the blog entry are specific to keeping the product of velocity and pipe internal diameter within certain limits for preventing accumulation of static charge. In the blog entry, it clearly sates that if the conductivity is less thea 50 pS/m or unknown and sulfur content less than 50 mg/kg (ppmw), the product of velocity and pipe internal diameter should not exceed 0.5 m2/s.

 

Assuming that you don't know the conductivity of the fluid being loaded and also the sulfur content, you still have a conservative lower flow rate for prevention of static charge buildup considering a value of 0.5 m2/s.

 

Regards,

Ankur.

 

 

Using that equation for a 12" MLA (ID = 0.305m), you will get 1.64 m/s

 

That is clearly unrealistic which is some way below the 7.0 m/s by OCIMF for preventing static electricity in accumulator liquids. 

[colt16]

Sorry, am giving this topic a little bump for more opinions.

[DANA-IF]

Static charge due to high flow velocity has nothing to do with road tanker or marine loading. The guidelines in the blog entry are specific to keeping the product of velocity and pipe internal diameter within certain limits for preventing accumulation of static charge. In the blog entry, it clearly sates that if the conductivity is less thea 50 pS/m or unknown and sulfur content less than 50 mg/kg (ppmw), the product of velocity and pipe internal diameter should not exceed 0.5 m2/s.

 

Assuming that you don't know the conductivity of the fluid being loaded and also the sulfur content, you still have a conservative lower flow rate for prevention of static charge buildup considering a value of 0.5 m2/s.

 

Regards,

Ankur.

Hello, intreresting blog

 

but :

Does 7m/s is a normal velocity , that seems too high ?

 

In API 14E , the liquid line velocity shouldn't exceeds 5 m/s 

Regards !

[ankur2061]

Different standards advocate different velocities. Also different operating companies advocate different guidelines for velocity and pressure drop based on their operating experience.

 

So there is no single guideline which is universally applicable. Depends on operating experience and a combination of other factors such as capital cost, operating cost, safety, reliability and profitability.

 

If you think 7 m/s is high then you must see the NORSOK standards for offshore O&G industry which advocate even higher velocities and limit velocity based only on MOC of the pipe. They have arrived at velocities based on their owns studies of cost, safety, reliability and profitability. Many companies in offshore O&G exploration follow NORSOK standards and consider them to be at par with other standards such as API.To me, the reason for even higher velocities is obvious. Space on offshore platforms is available at a premium. If you have conservatively low velocities, you will require bigger pipes for a given flow which will tend to increase the platform size and thus greatly increase the cost of the platform and ultimately the cost of oil and gas production.

 

Velocities in pipes has been intensively discussed on "Cheresources" and there is a free spreadsheet on velocity guidelines of various standards posted by our member Ajay Satpute in the download section.

 

Regards,

Ankur.

[DANA-IF]

Different standards advocate different velocities. Also different operating companies advocate different guidelines for velocity and pressure drop based on their operating experience.

 

So there is no single guideline which is universally applicable. Depends on operating experience and a combination of other factors such as capital cost, operating cost, safety, reliability and profitability.

 

If you think 7 m/s is high then you must see the NORSOK standards for offshore O&G industry which advocate even higher velocities and limit velocity based only on MOC of the pipe. They have arrived at velocities based on their owns studies of cost, safety, reliability and profitability. Many companies in offshore O&G exploration follow NORSOK standards and consider them to be at par with other standards such as API.To me, the reason for even higher velocities is obvious. Space on offshore platforms is available at a premium. If you have conservatively low velocities, you will require bigger pipes for a given flow which will tend to increase the platform size and thus greatly increase the cost of the platform and ultimately the cost of oil and gas production.

 

Velocities in pipes has been intensively discussed on "Cheresources" and there is a free spreadsheet on velocity guidelines of various standards posted by our member Ajay Satpute in the download section.

 

Regards,

Ankur.

Hello ; 

Thanks a lot MR.Ankur for you reply ;

 

on my current task I'd like to size a line with two downloading arm ( JET A-1 PRODUCT)

 

I'm in trouble to find  maximum velocity guide  for this line since it is located after pump dicharge  .

 

I'm wondering if you could guide me on that ?

[ankur2061]

OCIMF recommends 7 m/s for marine loading arms. Some good information is available at the following link:

 

http://pipelineandga...-considerations

 

Regards,

Ankur.

[DANA-IF]

OCIMF recommends 7 m/s for marine loading arms. Some good information is available at the following link:

 

http://pipelineandga...-considerations

 

Regards,

Ankur.

I FORGOT TO SAY THAT MY TASK IS ONSHORE AND NOT MARINE 

 

I'm wondering if onshore and offshore have the same recommendations ?

 

REGARDS 

[ankur2061]

Marine loading arms means loading arms for marine vessels (ships) and can be onshore or offshore. Onshore loading arm here means from storage terminal on land to ship berthed in jetty.

 

Regards,

Ankur.

Edited by ankur2061, 11 September 2015 - 10:30 AM.

[DANA-IF]

Marine loading arms means loading arms for marine vessels (ships) and can be onshore or offshore. Onshore loading arm here means from storage terminal on land to ship berthed in jetty.

 

Regards,

Ankur.

 I HAVE ALSO CALCULATED THE EROSIONAL VELOCITY FOR JET A-1  : its around  5 m/s 

 

Then 7 m/s is higher than 5 m/s !

 

 

I'm wondering if  I Should take into consideration the erosional velocity ?

 

Best regards !

[ankur2061]

7 m/s is for loading arm, not for the pipe. Loading arm size can be based on a maximum velocity of 7 m/s.

 

Jet A-1 is single phase (liquid) and is not supposed to contain any solid particles, so I am not sure whether there is really any significance of erosional velocity. The API 14E erosional velocity equation is meant for two-phase fluids that may or may not contain solids.

 

You want to play safe and stick to guideline of erosional vlelcoity, then go for 3 m/s (60% of 5 m/s). You also need to check the acceptable pressure drop in the line for a selected velocity and line size so that you have a minimum pressure at the loading arm inlet as specified by the loading arm manufacturer. In one project that I had worked, the loading arm inlet pressure was specified was 2.5-3 barg to ensure filling of the tanker based on pressure drop in the arm and the static lift up to the manifold of the ship.

 

Regards,

Ankur

[DANA-IF]

Thanks a lot MR.ANKUR for the explanation 

 

Regards !