Welding HDPE pipe and pressure drop
Welding HDPE pipe and pressure drop
(OP)
When PE pipe is thermal welded the weld leaves a bead inside the pipe.
How much does this bead effect the pressure drop down the pipe?
We have line (90mm OD 10mm wall) that does not flow any where near the flow it should but the pressure drop calculation did not include the effect of the weld bend.
How much does this bead effect the pressure drop down the pipe?
We have line (90mm OD 10mm wall) that does not flow any where near the flow it should but the pressure drop calculation did not include the effect of the weld bend.





RE: Welding HDPE pipe and pressure drop
How long is the line, and what is the fluid? What was the flow you expected, and what are the upstream and downstream pressures?
RE: Welding HDPE pipe and pressure drop
The flow we want is 5.5 l/s DP = 5.5 bar
we get 1 l/s DP = 12 bar.
fluid is water @ 48C
The line is above gound and the run is flat.
thanks
Kevin
RE: Welding HDPE pipe and pressure drop
1. Try reversing the flow and see if any debris comes out.
2. Run a sizing pig through until it stops; replace the defective segment/segments.
RE: Welding HDPE pipe and pressure drop
Some less competent manufacturers keep to the highest tolerance wall because they cannot control the extruders well enough. They tend to be back yarders who use lots of regrind, have low overheads, old machines and die heads and no technology back up. The additonal resin used is countered by their low caost of operation.
Dont buy PE on price buy on technology. The cost of a failure will soon outweigh the savings you have made.
As far as the weld bead is conserned you could always cut it out. The Daisy Gorseline cutter is one such tool but I believe there are others out there.
RE: Welding HDPE pipe and pressure drop
He = K*v1^2/2Gc
K= (1- (d1/d2)^2)^2
He = headloss
K = K factor
d1 = effective diameter of pipe at bead
d2 = diameter of pipe
Gc = gravity
v1 = velocity at d1
Hydrae
RE: Welding HDPE pipe and pressure drop
RE: Welding HDPE pipe and pressure drop
I did a calculation treating the welds as an orfice plant and got a very small orfice to give the measure drop.
After a bit more site work we found some rocks on the line. all OK now
Kevin
RE: Welding HDPE pipe and pressure drop
The equation is derived as the resultant pressure recovery down stream of the orifice using conservation of momentum and energy. The energy goes into the small eddies downstream of the expansion as heat. Look up in your fluids book of all the minor losses a 'sudden expansion' is the only one determined with an equation, all the other losses have a lookup table for the K value based upon experimental results.
Kevin
Where the rocks on or in the line?
Hydrae
RE: Welding HDPE pipe and pressure drop
Kevin
RE: Welding HDPE pipe and pressure drop
RE: Welding HDPE pipe and pressure drop
For the orifice loss it would be reasonable for this simple approximation to assume that the slight increase in velocity is not recovered thus Hl = (Vo - Vp)^2/2g. Vo = V orifice will be Q/(cc.do).
Vp = average pipe velocity.
You would then need to reduce this by a factor (say 50%) to account for the fact that the friction factor is for real pipe and already includes bead losses.
If losses are more than anticipated it usually means that there is an obstruction in the pipe as is the case here.
RE: Welding HDPE pipe and pressure drop
RE: Welding HDPE pipe and pressure drop
Technical Note PP 828-TN
Internal Fusion Bead Flow Resistance
For pressure piping applications, tests show that polyethylene pipe with internal fusion beads has a surface roughness of 7 x 10-5 feet, which corresponds to typical surface roughness values for the design of smooth pipes and to a Hazen-Williams C-factor for water at 60°F of 150. AWWA and Factory Mutual Research both recommend a C-factor of 150 for the design of polyethylene water pipe using the Hazen-Williams equation.
When these surface roughness or C-factor values are used in design, the effects of internal fusion beads are automatically factored into the results, and flow resistance due to internal fusion beads does not need to be considered separately.
Hope this helps