1. Corrosion of Brass quick connectors on Yoke Cooling circuit
Norbert FRANK - PH-CMX

2. Problem: After investigation:
High Temperature in radial cable tray on YB0 sec. +3 in Nov > no flow in this sector!
Slight and constant decrease in flow observed since Feb. 2011
After investigation:
One blocked quick connector (type QC4) found in thermal screen output side of sector +3 (YB0) in Feb. 2012
Norbert FRANK - PH-CMX

3. While dismounting, all of their stems were breaking
Further 4 quick connectors (type QC4) have been changed same problem of corrosion
While dismounting, all of their stems were breaking
Chemical Analysis (EN/MME-MM)
Initial Components (C.o.C. Swagelok)
Fe %
Cu %
Zn %
Pb %
Zinc is almost disappeared, as in leaching phenomenon, typical of brass
Elmt
Line
Element %
Sigma %
Atomic % Fe K
0.42
0.21
0.47 Cu
98.86
0.81
98.67 Zn
0.95
0.65
0.93 Pb M
-0.23
0.44
-0.07
Picture EN/MME-MM
Picture EN/MME-MM
Norbert FRANK - PH-CMX

4. After having changed these 4 quick connectors (type QC4), YB0 main flow increased about 4 l/min
One bigger quick connector (type QC6) has been changed -> same symptom of corrosion
Pictures: M. Droege ETH
Norbert FRANK - PH-CMX

5. Status, geography and accessibility
Quick connectors serve the radial thermal screen panels, vac-tanc thermal screens and HO-RBX boxes.
In case of failure: no leaks, just blockage of the cooling loop (broken stem should stay blocked in the quick connector). We have proven in November 2011 that we can most probably survive with no cooling on one sector. The temperature of the HO-RBX boxes should be observed, but in principle, they should also survive without cooling.
Geography:
96 QC4 connectors (mobile wheels, RTS) – not accessible
12 QC4 connectors (YB0, RTS) – 6 accessible – 5 already changed
48 QC4 connectors (mobile wheels, HO-RBX boxes) – not accessible
48 QC4 connectors (YB0, HO-RBX boxes) – not accessible
12 QC6 connectors (YB0, RTS) – 10 accessible – 1 already changed
24 QC8 connectors (YB0, VacTS) – accessibility has to be checked – 0 already changed (vac-tanc thermal screens, Rack cooling circuit)
Changing of a accessible connector requires:
Cooling loop to be closed (pump can stay on, no need for stopping the circuit)
Thermal screen panel shall not be emptied
The same quick connector exist in Stainless Steel and can be replaced with no further part replacement (to be checked regarding corrosion: compatibility between existing brass nut + copper pipe and new stainless steel quick connector)
Changing one connector takes about 20 min, once the accessibility is granted to the sector
Norbert FRANK - PH-CMX

6. Conclusion
“…A dezincification has occurred in the brass stem, which is a typical form of corrosion of brass (selective corrosion of brass is called dezincification or leaching). As expected, de-zincified areas show a relatively porous and weak layer of copper and copper oxide. Usual analyses in de-zincified areas indicate 90 to 95% Cu, which is indeed the main element signal in our analysis of corroded areas. This usually occurs when brass is used in specific environments. Dezincification of brass components in demineralized water has already been demonstrated in the power convertors of LHC…”(EN/MME-MM, EDMS , )
No further tests on Yoke cooling circuit have been performed this year (no flow/pressure variations)
Connectors need to be changed
Norbert FRANK - PH-CMX