Gas Flow Erosion Pattern Through Orifice

[johnchrc]

Does anyone know or have seen how an orifice in casing or tubing will erode when flowing gas through it? For example, we have been asked to pump N2 through a device down the annulus and back around the tubing through a 15/16" orifice. This would be simalr to flowing through a sliding Sleeve with just one small hole instead of multiple holes or slots. I don't have gas rates or volumes.

Assuming the flow erodes the steel when turning the corner, will the hole erode preferentially in one direction? perhaps a slot pattern eroding vertically from top to bottom?

Any input would be appreciated. Thanks.

 

[hacksaw]

errosion is not usually a problem. what sort of pressure drop are you dealing with?

 

[johnchrc]

I don't know what to expect. I have learned this is for N2 Gas unloading for an underbalanced drilling application. I have been given the hole size the customer wants and not much else. I need to have drawings in the shop end of week so I have already started detailing parts.

I am now more concerned about the impingement surface directly across from the hole. A Sleeve inside the ported housing is used to close off communication with annulus. If too much metal is removed, the Sleeve may not seal when closed. I thought I could position the hole such that it would allow for the most metal loss before failure.

What I need is carbide or boride choke inserts directly opposed from each other. I assume if this initial prtotype is promising, we will have the oppurtunity to design a "commercial" product.

 

[hacksaw]

you are dealing with product specific knowledge. you need to find out what work has been done before and spend a little time with someone who has worked with that application before, good luck

 

[johnchrc]

I agree.

This is a case of Marketing and Sales telling Engineering what they want instead of what they need. Those department heads seem to have more stroke than our Engr. Manager.

 

[zdas04]

The critical component in the analysis is the pressure drop across the orifice. If it is enough to give you velocities greater than 0.6Mach then the N2 stream will have a density on the order of liquid and a stream that dense moving that fast will have a very real potential to erode the downstream piping. If the choke is immediately upstream of an elbow or the backside of a tee, and you are greater than 0.6M then your mean time to failure could easily be measured in single-digit days.

A significantly slower stream is unlikely to cause erosion unless you are carrying errosive products (like frac sand, drill cuttings, or drilling mud), then you've created a sand-blaster/errosive-cutter with all the associated problems.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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