Help!!! B31.3 Line Sizing Assistance

[Berenger]

I posted this on the mechanical engineering forum, but got no assistance. So I thought I'd re-post here and, hopefully, get some help.
==========================================================================================================================================Can anyone explain explain the principal difference between B31.3 and B31.8. I know 3 is for plant piping while 8 is for gas transmission, but that is the extent of my knowledge.

I also created a line list based on the pipe schedule found at

http://www.engineersedge.com/pipe_schedules.htm,

but was told that this chart is based on B31.8. All the charts I have seen are identical to this one. Does anyone have a pipe schedule chart for B31.3? Can anyone share a pipe calculation spreadsheet for B31.3? Finally, what are the acceptable design factor and temperature correction factor for B31.3?

Thanks. Any and all assistance is appreciated.

 

[TD2K]

On the whole, those pipe schedules are the commonly available thicknesses I'm familiar with for inplant piping, they don't specifically limit themselves to B31.3 or B31.8 or any other piping code. I'll add some of those sizes are odd: 4.5", 7", 9" for example, I don't recall seeing those before on piping tables. Others such as 5" pipe I have seen listed elsewhere but in reality are rarely seen in the field. API 5L also lists standard available piping thicknesses but more for pipelines. These aren't the only thicknesses, you can always specify a required thickness though that's only economical for long runs of pipe like a cross country pipeline where the savings in weight and handling costs outweigh the additional cost to procure the pipe.

For any of the piping codes, they identify the formulas and any factors that need to be applied. The formulas and factors are not the same between the various codes. You should get a copy of the codes and look at the formulas and see how the required thicknesses vary for different design conditions. Under a specific code, you calculate the minimum wall thickness required to withstand the pressure. You then add any mill tolerances and corrosion allowances and then select the next available wall thickness that is greater than the minimum you calculate. You may also have clients' preferences to take into account. For example, many companies will specify minimum sch 80 pipe for 2" and below even if your calculations indicate sch 40 is adequate.

 

[Berenger]

Thanks TD2K. I did get the copy of the code. Using a "temperature correction" of 1 and a "design factor" of 0.5, I calculated the ID using an excel spreadsheet. I also confirmed my calculations using ProMax.

However, when I emailed my spreadsheet to the senior engineer, he said "this calculation was done using B31.8. Can you please re-do using B31.3". I have re-calculated but still get the same figures. So, I'm not sure if he meant the pipe diameters are wrong...or that the temperature correction and design factor that I used are wrong.

 

[TD2K]

I'll have to dig up the codes tomorrow, I don't have them here. B31.3 does not have a temperature de-rating factor that I recall (B31.8 does as well as an area factor that isn't in B31.3).

 

[TD2K]

Why don't you go over your numbers and approach with the other engineer for their comment?

 

[Berenger]

I have gone over them with some other engineers and they don't see anything wrong with it. The senior engineer is one of those curt guys who you only want to interact with if necessary.

 

[Latexman]

Sounds like it's necessary to me. Everyone makes mistakes. The sun don't shine on one dog's ass every day!

Good luck,
Latexman

 

[dcasto]

Pipe schedules are generic, they are not a function of piping codes. There is nothing that says you cannot use a custom wall thickness either. Pipeline pipe comes in many thicknesses just as "tubulars" used in drilling and production.

The equations for calculating MAOP are different in each of the Standards and if you want to do a B31.8 table, you'll have to use all 5 of the different design factors available.

Both 31.3 and 31.8 have temperature deratings, but, the flanges derate for temperature different than the pipe and they normally limit the MAOP before the pipe does.

Next, B31.3 does allow much of an upgrade in MAOP based on pipe yeild strenght, but that's another topic for another day.

 

[Berenger]

Thanks, dcasto, your post was of tremendous assistance. I did seek assistance from the senior engineer and helped a bit. I also just bought a copy of b31.3 and currently reading through. At first glance, I noticed a table for temperature corrections. However, I didn't see a table of design factors (they referred to A304.1.1, but that table is not for design factors). "Design factor" was mentioned quite a bit in standard. Do you know what table details the design factor or do you know where I can get those?

*I'm still reading through the standard and, as you know, it's over 450 pages. So, any assistance is appreciated.

 

[BigInch]

B31.3 uses allowable stresses, so there are no visible design factors (they are included in the allowable stresses). Another notable difference might be the wall thickness, which, if not specified in the pipe purchase order as a minimum of -0%, may leave you with a -12.5% production tolerance, ie. 87.5% of 1/2 inch, whereas B31.8 always uses the nominal wall thickness, such as 1/2 inch.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[OilToil]

Another difference is in the inspection and testing requirements. Some key differences that frequently come up for the work I'm involved with are that 31.3 requires 5% x-ray for the circumferential welds, whereas 31.8 I beleive has different requirements for x-ray depending on what %of SMYS the line will operate at. 31.3 also pretty much requires a hydrotest except under limited circumstances, whereas 31.8 again has different requirements depending on operating pressure.

 

[Berenger]

Thank you, all, for your assistance. I finally finished reading the standard and believe I'm an "expert" now. I have done 3 line lists since then. Once you do one, then you've done it all.