70/30 Cu-Ni Wall thickness calc. 3

[prens11us]

hello all,

I want to calculate wall thickness of 70/30 Cu-Ni (B466) pipe.

I am using the formula that is from B31.3 para 304.1.1. Is the procedure same as carbon steels.

Should I add corrosion allowance to pressure design thickness, or assume CA as zero?.

Finally are the wall thicknesses of the different schedules are as same as for the carbon steels.

thanks in advance.

best regards

prens

 

[metengr]

If you intend to calculate the minimum wall thickness using ASME B31.3, you need to use the allowable stress value for Cu-Ni pipe from Table A-1. As far as corrosion allowance, this is up to the designer.

No. Once the pipe OD has been selected, the wall thickness will be dictated by your design calculation from B31.3.

 

[jnleroux]

The standard wall thicknesses for seamless copper pipe can be found under ASME II, SB-42, "Specification for Seamless Copper Pipe, Standard Sizes".

The ODs are the same as carbon steel, but the thicknesses are different. For example, standard wall for a 1" carbon steel pipe is 0.133", where std. wall for copper is 0.126" and XS is 0.182".

As far as corrosion allowance, it depends on the corrosion mechanism. Unless there is absolutely no chance of any corrosion, it is a good idea to have some allowance. Otherwise, as soon as you have any pitting/corrosion, you will be beyond retirement thickness. If you use ASME B31.3 for your calculations before you choose your pipe, you will probably find that you'll have more wall than needed for pressure retention. For small bore piping, you will probably find that the thickness required for the pipe to support itself will be greater than the thickness required for pressure retention. Use the thicker of the two as your base design thickness and the remainder rounded down to the nearest 1/8" or 1/16" as your corrosion allowance.

Best of luck,
John

 

[sjrfc2]

I'm pretty sure the SB-42 is for copper pipe where this would be copper-nickel. SB-466 (95) has size info for the CuNi in X1.1.

Mil-T-16420 identifies classes (200, 700, etc..) for CuNi.

http://www.premiercopper.com

has info available online for sizes. I think they're the same as some of the as the SB-466 sizes.

Velocity especially in seawater can cause erosion of the CuNi piping. I'm not sure how much better it is for 70/30 vice 90/10 but its something to consider when you are selecting pipe sizes , walls, and materials.

http://www.copper.org/applications/cuni/txt_applications_for_seawater_service.html#Erosion

Provides some info. I'm not sure a flat out velocity number is OK. I've seen it further restricted with smaller sizes and I think its based on Reynolds numbers.

Additionally any steps including backing rings can cause localized erosion in the piping so you should consider fitting design and joint requirements as well.

 

[prens11us]

john and sjrfc2 thank you for these valuable help.