Transcript New developments in fabricated Tees‐A quality Assurance Design

NEW DEVELOPMENTS IN FABRICATED TEES –
A QUALITY ASSURANCE DESIGN GUIDELINE
A.C. Seibi and R. J. Lawrence, GPPA
Outline
 Background
 Approach
 Quality Control
o Lab. Tests
o Finite Element Modeling
 Results & Discussion
 Conclusions & Recommendations
Background
Background
Background
Design????
Background
Do we have to strictly follow ISO 4427 ????
f  0.8
f  0.5
Approach
1. Search for field reports of failures.
2. Examine welding fabrication process.
3. Perform finite element analysis.
4. Carry out laboratory burst tests on elbows
and tees.
5. Compare results of 3. and 4.
Preliminary Findings
1. Very few field failures of pipe
fittings.
2. Overlapping beads at tee joints may
present weakness in fittings.
3. Soaking time for large diameter
pipes should be revisited.
4. Bead not welded properly
QC: Lab Results
Parrot beak
Pipe yielding
1st Joint
2nd Joint
Long Term Test (Tees).
12.4 MPa for 100 hrs at 20 oC
5.4 MPa for 165 hrs at 80 oC
63 – 250
Size (mm)
560 - 900
2000
Pass
Pass
Pass
0.9
Pass
Pass
---
0.95
Pass
Pass
---
1
0.8
Fail
Pass
Fail
Pass
--Pass
0.9
Pass
Pass
---
0.95
Pass
Pass
---
1
Fail
Fail
---
Temperature Derating
(oC)
factor
0.8
20
80
QC: Finite Element Modelling
Elbow
Tee
FEM Results
60
50
Pressure (bar)
40
30
20
10
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
Displacement, U/D
Press. vs. displ
Stress contours
Results
Bend
Pressure
Pressure
Size
Angle Thickness
FEA
Experimental Error
(mm)
(deg.)
(mm)
(bar)
(bar)
(%)
317.5
45
12.7
21.8
23
5.39
225.6
90
15
33.8
37.5
9.87
167.1
90
15.1
46.6
49.2
5.28
161
45
14.9
54
60
10.00
225.8
45
13.8
34.95
34.9
0.14
Difference ≈ 0.1 – 10%
Max. s & e not at the same place.
Why?
Displacement
contours
Stress concentration
Deformed shape
Failure occurs at intersection due to
viscoelastic material behavior
FEM Results
Longitudinal
strain
Transverse
strain
Practical Solution - UPI
 UPI developed a 2000
mm reducer tee.
 No worry about pipe
derating.
FEM Results
It was recommended to create fillets at the inner
and outer sections of the junction.
Conclusions
1. A derating factor of 0.8 for modern PE100 like
HE 3490 LS pipe tees can be safely accepted.
2. Most failures in tees take place in either 1st or
2nd weld. Need further investigation.
3. FE results showed a good agreement with burst
pressures of pipe bends.
4. FE results showed that the max. stress is
concentrated at the tee junction and that
potential failure is anticipated to take place at
the intersection of the welds.
Recommendations
1. Need to understand reasons behind tee failure
along the welds.
2. Must develop a strain based failure criterion for
plastic pipes and fittings.
3. Damage mechanics should be considered in FEM
to better understand failure modes in fabricated
pipe fittings.
4. Should take a look at the soak time in welding of
large size fittings.