7 replies to this topic

[mtwk]

Hello,

I'm a mechanical engineering student on placement at a steam company and I've been asked to investigate the erosion of 90-degree pipeline elbows. I've suggested giving this to a chemical engineer but there aren't any here. I started by trying to calculate the rate of mass removed from the elbow by the fluid so that I could determine how long it would last before becoming unsafe. I assumed, probably wrongly, that there would be an equation relating the mass flow and temperature in the pipeline with the mass lost from the elbow, but I couldn't find anything obvious online.

Please could I have some help finding which equations to use for this problem or which books and journals to read. Is it even realistic for me to attempt to continue?

Some typical conditions might be:

Fluid: Dry steam (no solid particles)
Pressure and Temperature: 101.5 psi (7bar) gauge at 339 deg F (170.5 deg C)
Flow rate: 882pounds/h = 0.245pounds/s (400kg/h = 0.11kg/s)
Pipeline: Steel, 2inch = 50mm, friction factor 0.031

Thanks,

Mitchell

[gvdlans]

Why do you expect that the pipe will lose mass, when there is dry steam (no particles) flowing through it? What would be the mechanism?

My estimation is that pipe mass reduction because of erosion will be zero.

[mtwk]

I thought that the force of the water on the pipe wall would slowly remove material, like a river on its banks. Have I got the wrong idea of what's going on? Would erosion only occur after corrosion?

Thanks for replying,

Mitchell

[gvdlans]

Dry steam does not contain liquid water (by definition). If it is not dry there would be a point, although I still expect the effect to be next to nothing. Note that steel is a lot stronger/tougher than a river bank.

[mtwk]

Understood, thanks for your help.

Mitchell

[gvdlans]

You're welcome!

In wet steam lines there is a phenomenon called erosion-corrosion, that is described here: http://corrosion-doc...ion/erosion.htm

I understand that this is mainly relevant when soft alloys are used as pipe material

[vittorio6]

Hello,

I'm a mechanical engineering student on placement at a steam company and I've been asked to investigate the erosion of 90-degree pipeline elbows. I've suggested giving this to a chemical engineer but there aren't any here. I started by trying to calculate the rate of mass removed from the elbow by the fluid so that I could determine how long it would last before becoming unsafe. I assumed, probably wrongly, that there would be an equation relating the mass flow and temperature in the pipeline with the mass lost from the elbow, but I couldn't find anything obvious online.

Please could I have some help finding which equations to use for this problem or which books and journals to read. Is it even realistic for me to attempt to continue?

Some typical conditions might be:

Fluid: Dry steam (no solid particles)
Pressure and Temperature: 101.5 psi (7bar) gauge at 339 deg F (170.5 deg C)
Flow rate: 882pounds/h = 0.245pounds/s (400kg/h = 0.11kg/s)
Pipeline: Steel, 2inch = 50mm, friction factor 0.031

Thanks,

Mitchell

If you need to calculate erosion then you can look at API RP 14E or better to the DNV Det Norske Veritas Standard - DNV Recommended Practice RP 0501; Erosive Wear in piping Systems that you can find at http://www.dnv.com/

V

corrosion prevention

[riven]

I would not expect erosion due to particles or wet steam. However your pipe will certain feel fatigue especially if it is old. For example if the pipeline has been under stress for that last 10 years at say 600C and 40 bar then I would expect something to happen.

Your best bet in this situation is to document your situation carefully (inlet and outlet temperature pressure, flow conditions etc) and check the maintenance records to see how old this pipe is and for how long it is in service. Then contact either a more senior engineer, the pipeline manufacture or even check the maintenance records again to see if the pipeline is past itsrecommended lifetime. If it is not, there should be no reason to change unless it was used incorrectly.