2D Elbow ASME Standard

There are standards covering general piping systems which would apply.

These standards have requirements for pipe bends and elbows which do not fall under the scope of B16.9. They have limitations on pipe wall thinning during bending, methods of achieving the bend and intrados "wrinkling" in the finished bend.

The standards are ASME B31.1 and B31.3 ....

Why must your elbows be 2D ???? ....... I can't imagine a design situation where they must be 2D and 1.5D is not acceptable ....

It is a special requirement for one Lube oil line which has very less flow rate(only by gravity). So, in that case a 1.5D elbow's radius won't allow flow in certain operating conditions. Hence a 2D elbow is necessary. Can you tell which is the exact standard?

Look for "sweeps" instead of elbows.

Lyn,

Please elaborate what do you mean by sweeps? I am not able to get it.

A "swept" bend. Look it up on Google

Now, we are getting to the root of the problem.

Is somebody pulling your leg? Who would ever have computed that a 1.5D elbow wouldn't do the job, but a 2D elbow would? If it is a gravity line, is there any significant pressure involved? If not, what is the worry about a standard?

The client is saying that the flow of lube oil is by gravity. Hence a 2D elbow with a gradual change in slope will make it easier for the oil to flow rather than a 1.5D elbow.

BEND SPECIFICATIONS

5.1 Bends

A pipe bend made to this specification and verified for pressure design in accordance with ASME B31.3 shall be suitable for the same service as the pipe from which it is made.

5.2 Out of Roundness

Flattening of a bend, is measured by the difference between the maximum and minimum outside diameter at any cross section. For 1½D bends, out of roundness shall not exceed 5 percent of the nominal outside diameter for internal pressure, and 3 percent for external pressure. For 3D bends, out of roundness shall not exceed 3 percent. (See FIG. 1)

5.3 Dimensional Tolerances

Degree of bend is to be held to plus or minus 1 degree. Overall spool length will be held to plus or minus 1/8 inch. All centerline-to-centerline or centerline-to-end face dimensions will be plus or minus 1/8 inch. (See FIG. 2)

5.4 Wall Thinning

Wall thinning of 1½D and 3D bends, as measured by the difference between the actual thickness of the pipe "A" and the minimum thickness "B" on the outside of the bend shall not exceed 18 percent of the actual thickness for 1½D bends and 12 percent for 3D bends. (See FIG. 3) Maximum allowable working pressure should be calculated using the following formula:

For 1 1/2D Bending 1P= 2SE[.82t -c]
D

For 3D Bending 1P= 2SE[.88t -c]
D

P - Maximum Allowable Working Pressure
SE - Allowable Stress
t - Actual Pipe Wall Before Bending
c - Corrosion Allowance
D - Outside Diameter of the Pipe