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Erosion Due To Flow




Erosion can be defined as the mechanical loss of material by the impact of solid particles (e.g. sand, certain hard scales, catalysts) and / or liquid droplets.

Erosion caused failures are not new. The oil and gas industry has suffered and continues to face many failures that can be attributed to erosion.

Under aggressive operating conditions, flow velocity limits and thus the production limits are set to avoid erosion. If the velocity limits are overly conservative (lower values) then an oil company can suffer production losses and if they are too optimistic (high velocities) there is a serious risk of erosion damage and the loss of system integrity.

Erosion mechanism can be a combination of several factors in flowing fluids. Some of the erosion mechanisms are described below:

Liquid Droplet Erosion

This form of ersoion happens due to the formation of very high pressures and stresses at the point where the liquid droplets contact the pipe wall. Wet gas with an annular mist flow regime can cause droplet impact but generally droplet erosion is a problem in very high velocity systems.

Erosion-corrosion

Erosion-corrosion occurs in environments that have the potential to be both erosive and corrosive. The erosion and corrosion can either be independent, in which case the total material loss is the material loss produced by each mechanism in isolation, or synergistic, in which case the total material loss is greater than the sum of the independent mechanisms of erosion and corrosion. It is important to note that erosion-corrosion is not a pure erosion phenomena.

Cavitation-erosion

Cavitation is caused by the high energy collapse of vapor bubbles (or cavities) in a liquid flow stream as a result of pressure recovery following pressure reduction to a value below the vapor pressure of the liquid at the flowing temperature. Cavitation-erosion is not caused by the impact of solid particles or liquid droplets, but by the impact of a very high velocity liquid pulse onto the solid boundary from a collapsing bubble.

High pressure drops using single-stage control valves and sharp directional changes (e.g. short-radius elbows) can result in cavitation-erosion in piping systems. Multistage pressure reduction and long radius elbows provide better protection against cavitation-erosion.

Effect of flow patterns on erosion in multiphase flow

The flow patterns that are encountered in multiphase flow can be described as follows:
a. Bubble Flow
b. Plug flow
c. Stratified flow
d. Wave Flow
e. Annular Flow
f. Slug flow
g. Churn Flow
h. Mist Flow
With the exception of stratified flow all the flow patterns that have been described above are commonly encountered in horizontal, vertical and inclined flow.

The flow pattern is very important in determining the erosion cahracteristics of multiphase flow, i.e flow containing solid particles. The major factors that effect erosion in multiphase flow are:
1. The phase that the soild particles travel in and
2. How the phases are distributed in various patterns

Due to the higher density and viscosity of the liquid compared with the gas phase, solid particles carried in the liquid phase follow the streamlines more closely and are less likely to impact the pipe wall if the fluid changes direction. Hence, for the same mixed phase velocities, flow regimes where the particles are carried in the gas exhibit higher erosion rates than flow regimes where the particles remain in the liquid.

In annular flow the particles are carried in both the liquid film and the gas core. The phase distribution in annular flow usually consists of a slow moving liquid film on the pipe wall and more rapidly flowing gas core containing liquid droplets.

In bubble flow the low relative velocity between tha gas and liquid phases means that there is very little entrainment of particles into the gas phase. This results in all the particles being carried in the liquid phase. The liquid flows as a continuous phase with the gas fairly evenly distributed in it. As both gas and liquid flow at similar velocities the effects of direction changes (bends) and other fittings on the phase distribution is much less pronounced than in annular flow.

As with bubble flow, the relative velocities between the phases, in churn flow is low. However, the large amount of mixing and generally random distribution of the phases could lead to a small portion of the particles being carried in the gas phase.

API 14E- "Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems" as well as ISO 13703- "Petroleum and natural gas industries- Design and Installation of piping systems on offshore production platforms" provide calculation equations for erosional velocity in multiphase flow. The basic equation for calculating erosional velocity as per the above references is:

Ve = C*(1/ρm)0.5

where:

Ve = fluid erosional velocity, ft/s (m/s)
ρm = gas / liquid mixture density at flowing temperature and pressure, lb/ft3 (kg/m3)
C = empirical constant

The 'C' value as recommended by API 14E and ISO 13703 are as follows:

English Units:
C = 100 for continuous service; C=125 for intermiitent service; for solids-free fluids where corrosion is not anticipated or when corrosion is controlled by inhibition or by employing corrosion resistant alloys, values of C = 150 to 200 may be used for continuous service; values of 250 may be used for intermiitent service

SI units:
The values mentioned above should be multiplied by a factor of 1.22 (e.g. 'C' value of 100 becomes 122)

The mixed phase density may be calculated as follows:

Engllish Units:

ρm = 12490SlP + 2.7RSgP / (198.7P + RTZ)

where:

Sl = liquid specific gravity at standard conditions (water =1)
P = Operating Pressure, psia
R = Gas/liquid ratio, ft3/barrel, at standard conditions
Sg = gas specific gravity at standard conditions (air =1)
T = Operating Temperature, R
Z = Gas compressibility factor, dimensionless

SI Units:

ρm = 28833SlP + 37.22RSgP / (28.82P + 10.68RTZ)

where:

Sl = liquid specific gravity at standard conditions (water =1)
P = Operating Pressure, kPaa
R = Gas/liquid ratio, m3/m3, at standard conditions
Sg = gas specific gravity at standard conditions (air =1)
T = Operating Temperature, K
Z = Gas compressibility factor, dimensionless

Once Ve is known, the minimum cross-sectional area required to avoid fluid erosion is determined by the equation below:

English Units:

A = 9.35 + (ZRT/21.25P) / Ve

where:
A = minimum pipe cross-sectional flow area required, in2/1000 barrels liquid per day

SI Units:

A = 277.6 + (103ZRT/P) / Ve

where:
A = minimum pipe cross-sectional flow area required per unit volume flow rate, expressed in square millimeters per cubic metre per hour mm2/m3/h

However, recent studies on erosional velocity limits that the 'C' values given as per API 14E are very conservative. I had made a post related to the 'C' values for erosional velocities based on recent studies and also had provided the link for a "Society of Petroleum Engineers" (SPE) paper which discusses in detail about 'C' factors that need to be considered based on the solid content and the various piping materials. Below is the link for the post:

http://www.cheresour...per-api-rp-14e/

Hope the readers and members of "Cheresources" enjoy this rather lengthy blog entry.

I am looking forward to comments from all of you.

Regards,
Ankur.




Hi Ankur,
This is very interesting and more eloborated article.
Thanks,
Mani
Hello Sir,
Really very helpful.
Thanks
Amit.
Photo
Sherif Morsi
Jan 31 2012 09:44 AM
Hi Ankur,

A very interesting topic.
Bu could you please advise on the following:

1- What if I need to size a new line that has gas (single phase) with some sand coming from the wells through the flow line, How can I calculate the erosion velocity (P.S The API formula of erosion velocity is limited to two-phase flow)?

2- Same as above but with single-phase liquid lines carrying sand?

3- HYSYS has some values for "C" that differs with sand quantity, what do you of that?

Regards,
Sherif
Sherif,

1. Refer the link for gas wells:

http://www.sand-moni...s/sms_pdf15.pdf

2. For liquid pipelines the erosional velocity approach may not be considered. Instead, make sure that the velocity is restricted to a maximum of 4 m/s. This approach will ensure that other aspects of liquid pipeline such as "surge" are also addressed besides solids such as sand being carried by the liquid.

Regards,
Ankur.
Photo
nikoli nayda
Apr 29 2012 11:16 PM
Ankur,
Based on erosion, is there a similar method of predicting maximum flow rate in a pipe, that utilizes fluid density and temperature, as well as the density of the pipe, relative to solids-free fluids ?

Thanks for your thoughts.
Best regards,
Nick
Nick,

I am sorry but your quesion is not clear to me specially the part where you mention density of the pipe. Can you elaborate?

Regards,
Ankur
Hi Ankur,

The link for the pdf file http://www.sand-moni...s/sms_pdf15.pdf is not working any more. could you share the paper? my email is fucheng.t@gmail.com

thanks.
Dear Ankur Sir,

What criteria should be followed in heat exchanger regarding velocity for single phase fluid.

Dear Ankur Sir,

What criteria should be followed in heat exchanger regarding velocity for single phase fluid.


What type of heat exchanger? If S&T, then which side are you talking about, shell or tube. Excellent guidelines for tube side velocities are available in the Process Heat Transfer Master Excel file at:

http://www.cheresour...-heat-transfer/

Regards,
Ankur

What a wonderful piece of information. 

 

Thank you Ankur Sir

Thank you sir,

I always look upto you for inspiration , your blogs are quite informative 

Sir, i want to convince my colleague about limiting velocity in liquid flow .

We have the case that liquid is flowing in 6" line and for 2 meter length an with bends pipe line size is 2" . IN this 2" line velocity is about 20 m/sec .

How can i study the effect of such high flow on pipeline , adjoining pipeline fittings , structure and the system whole .

I want to equip my argument with more and more resoning and standard guidelines and not on thumb rule or general practices .

Please suggest me some literature and give your valuable suggeltions.

Regards,

sahil

Photo
ahmed abd elmonem
Oct 03 2013 07:21 AM

thanks for your work it is highly appreciated

Dear Ankur,

Link for PDF file provided above is not working any more. please update it again.

regards

Dear Ankur ,

This article is worth elaborated , Thank you for all your effort to guide the junior engineer! I've some question in this regards.

I'm designing an oil network with pipesim software( liquid single phase). to evaluate the velocity, which one will be considered for the design ? erosional velocity or liquid velocity ? and in which case do we use each one ?

thank you for sharing your experience on that.

Dear Ankur ,

This article is worth elaborated , Thank you for all your effort to guide the junior engineer! I've some question in this regards.

I'm designing an oil network with pipesim software( liquid single phase). to evaluate the velocity, which one will be considered for the design ? erosional velocity or liquid velocity ? and in which case do we use each one ?

thank you for sharing your experience on that.

Various operating and engineering companies have developed their own standards for velocity limits (lower as well as upper) for both liquids and gases based on several factors such as erosion, corroision, noise, vibration, slug formation and settling.

 

If you are working for a particular company or client try to find out if they have their own process standard regarding limiting velocities or they follow some other company's standard for this. Use these limiting velcoity numbers to ensure that the velocity is maintained between these limits. Cheresources itself has a line sizing criteria spreadsheet at the following link:

 

http://www.cheresour...velocity-check/

 

Regards,

Ankur

Ankur

 

How can I calculate the erosion velocity for single phase gas in a pipe?

 

The above API formula of erosion velocity is limited to two-phase flow?

Is the same formula to be used as above for gases.

for liquids u have clarified to limit the velocity below 4m/s.

 

PKS

Ankur

 

How can I calculate the erosion velocity for single phase gas in a pipe?

 

The above API formula of erosion velocity is limited to two-phase flow?

Is the same formula to be used as above for gases.

for liquids u have clarified to limit the velocity below 4m/s.

 

PKS

Erosion velocity for clean (no solid particles) and dry (no liquid droplets / mist) gas is not a matter of concern and can be ignored. The only issue for clean and dry gases is noise and vibration. Limiting velocities for clean and dry gases can be very high subject of course to the pressure drop limitations in the system

 

For wet gases containing trace amounts of solids, the API formula for 2-phase fluids for erosional velocity can be applied.

 

Hope this calrifies your query.

 

Regards,

Ankur.

Hi Ankur,

 

I am not new in this group, but this is my first time to discuss in this group.  I have a question regarding the limitation (maximum) amount of sand rate in our subsea pipeline.

 

Our pipeline facility has been designed with basis sand's limitation of 0.1 lb/MMSCF gas.  The gas is quite wet with water content 50 barrels for 270 MMSCFD gas.

 

Basis 0.1 lb/MMSCF is equal to 0.016 gram/sec. Mixture density (gas + water) is about 15.7 kg/m3 and sand assumed 2650 kg/m3, and gas flow rate is 30 MMSCFD.

 

Later on we found in our SAM (Sand Acoustic Monitoring) which install in the flowline (christmass tree), the measured sand rate is about 1.7 gram/sec. 

Refer to the SAM, actual measured sand rate which 1.7 gram/sec is much higher than our basis design.

 

Currently, we are requested to set the HH set point of sand rate at our subsea pipeline, but I believe our basis is even too low then the actual rate.

 

What do you think? 

 

I just read the article that 0.1 lb/MMSCF is the limitation for 'sand free' condition of pipeline?   And I read from DNV RP-0501, the maximum limit of sand rate is about 50 ppm W and from API 14 E is about 5 ppmv.

 

Shall I use 50 ppmw or 5 ppmv as the HH set of sand rate in our subsea pipeline?  

 

If this is sandy and no sand free, I guess our basis is wrong??

 

Please advice,

 

Thanks,

Tanti

Tanti,

 

What kind of sand are we talking about? Is it very fine silt or mud particles or siliceous sand?

 

Silt or mud particles will tend to stick to the walls of the pipeline and decrease the diameter of the pipeline thus increasing the velocity, but provide some protection to the metal of the pipleine due to coating. Whereas siliceous sand will be more erosive to the pipe metal.

 

If your sub-sea pipeline erosion rate with the present sand content is <0.1 mm/year then you need only ensure that the fluid velocity does not exceed 20 m/s. If the erosion rate is more than 0.1 mm/year you need to do a detailed analysis to arrive at a solution which include drastically reducing velocities or injecting inhibitors to slow down the erosion or in a worst case scenario change the metallurgy of the pipe.

 

API 14E is too conservative to be taken seriously as per my understanding.

 

Hope this helps.

 

Regards,

Ankur.

Hi,

Could you please give some information about Tube Side Two Phase Flow erosion Velocity in S&T exchangers? What Criteria will be applied?

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