Investigation on flexible hoses in DFBAs L Tavian

Investigation on flexible hoses in DFBAs L. Tavian 21 July 2009 With the contribution of B. Vullierme, EN-MME

Today situation • Detection of news leaks in the vicinity of two DFBAs (L 1 & L 3) with symptoms identical to the leaks found in the S 4 -5 in 2007 in flexible hoses. • The probability of new flexible-hose damages is high.

S 4 -5 case reminder

S 4 -5 case reminder TS-MME analysis

TS-MME analysis

TS-MME analysis Coloration visible à l’intérieur de l’onduleux

2007 investigation conclusion • The defects have been produced after the braid installation. – Multiple fusion points on the top of the corrugation equally distributed over 360°. (Affected length 10 cm). – No mixing of materials (braid vs corrugation) – Identification of several leak holes (min 3) – No visible oxidation. – No trace of mechanical wearing – No trace of chemical elements – No damage in between braid layers • Present most probable cause: Electrical phenomenon – Extremely short (<5 ms) or without oxygen or with a cleaning after the defect creations. – Today this electrical phenomenon is not identifed yet: • During flexible production (but followed by an efficient cleaning)? • During B 183 assembly activity ? (external welding activity with the DFB under vacuum? ) • In the tunnel after vacuum evacuation ? (welding/brazing operation? Ground current return with vibration ? ELQA ? )

Flexible-hose manufacturer recommendations • 1/Avoid bended flexible hoses. • 2/ Avoid high velocities in corrugated hoses which could create resonant vibrations resulting in premature fatigue failure. For braided hoses: < 50 m/s in gas if not bended < 25 m/s in gas if bended at 90° • What is the velocity seen by the DFBA hoses ?

Flow scheme D line C line (PT 961, TT 961) Kv max, =%, R Flexible hose PT 821 (L side only) Flexible hose configuration (straight or bended) not yet known (under investigation).

He velocity in flexible hoses S 1 -2 S 3 -4 S 2 -3 S 4 -5

He velocity in flexible hoses S 5 -6 S 6 -7 S 7 -8 S 8 -1

DFBA comparison At least 4 DFBA more critical !

Ultra-sonic vibrations • Is the flow able to produce ultra-sonic vibrations? – Velocity V= 25 to 100 m/s – Corrugation wave length: l= 0. 005 m – Frequency: V/l= 5 to 20 k. Hz • If yes, what about ultrasonic welding? – Could explain the multiple fusion points • If yes, what about the status of the other flexible-hoses? – Braid and corrugations stuck together waiting a thermal or pressure transient (cool-down and quenches) to develop leaks? • If yes, DFBA in L 5, L 7, R 7 & L 8 are critical. – Braid and corrugations affected but still free of relative displacement? • If yes, stopping the flow will stop the degradation process.

Proposal for consolidation of DFBAs in L 1 and L 3 • Replace the flexible hoses by smooth piping with lyres and/or pigtails (enough “free” space in the DFB vacuum vessel). – Integration study under way (collaboration with EN-MME) but as the “as built” configuration is not known, it will need in-situ adjustment. – Proposed internal diameter: 10 mm – As for the S 4 -5, repair intervention by EN-MME. • Limit the velocity (i. e. the valve opening) in the 16 DFBA circuits. Could have impact on: – The cool-down time of the Q 7 L. – The PIMs recooling process (time, autonomy) – The temperature uniformity for SCS test.

Consolidation road map (Already done as preventive measure) No mixing of materials Simultaneous development of several leaks