The 9th Symposium on Accelerator &ience and Technology, Tsukuba, Japan1993

Burst Failures of Water Cooling Rubber Pipes of TRISTAN MR
Magnet Power Supplies and Magnets
Tadashi Kubo
National Laboratory for High Energy Physics
1-1 Oho, Tsukuba-shi, Ibaraki-ken 305, JapanABSTRACT
In 1992, from June to September, the rubber pipes of magnet
and magnet power supply for water cooling burst insuccession. All the rubber pipes to be dangerous to leave as
those were had been replaced to new rubber pipes before the endof the summer accelerator shutdown.
INTRODUCTION
It passed about 7 years from the beginning of the TRISTANMR accelerator operation. It is strange that these failures
happened at the. same short period in the different situations
such as that one was in the MR tunnel and the other was in thepower supply stations on the ground. A number of and various
types of rubber pipes are used for power supplies and magnets.
Thus the detail analyses were carried out with respect to thevarious items. This document describes the processes of theanalyses of the failures and the final hnprovements.

RUBBER PIPES OF THE MAGNETSClassification of the rubber pipe3 types of the rubber pipes which were supplied from thesame company have been used for 4 types of the magnets.
Table 1a, 1b. show the parameters of the magnets.

The rubber pipes which happened to burst up to this time
were those of QB type magnets except for a few cases.
Past failures of the rubber pipes
We have experienced water leak failures of the rubber pipesof QA magnets in 1991. Magnet name is QW4 which islocated in the neighborhood of wiggler magnet, where theradiation level was very high at the accelerator operation. Thewater leak process was a little different from the failures at thistime, because the rubber pipe did not burst in any case, but thewater leaked from the couplers in both ends. And also therubber pipes had many cracks on the surface and lost
flexibility. It had been considered to be that these phenomena
came from radiation damage.
These effect does not come out after the radiation shield withPb.
Investigation of the burst failure
Rubber materials
The rubber pipe which has been strengthened with 3 layers
has been used for the magnet. The raw material of it is ethylenepropylene rubber of which abbreviated name is EPDM. Table
2. shows the structure.
Table 2. Structure of the rubber pipe
outside layer
middle layer
inside layer

Table Ia. Magnet parameters
Typemagnet namelength

QA
QB

0.8m
l.Om

Qc
B

1.5m
5.84m

height ofmagnet center

QF,QD,QS6 -7, QWI--4
QC4-6, QRF,DQSI-5
QC3
B

0.9m
1.5m
0.9m
1.5m
0.9m

Table 1b. Magnet parametersTypenumber ofmagnets

number of
rubber pipes

Diameter ofrubber pipes

QAQB

240
88408264

1920704320
641056

l/4"
318"
318"
112"
112"

Qc
B

ethylene propylene rubber
vinyl on fiber ( for reinforcement )ethylene propylene rubber

In 1982, the examination in quality about EPDM rubber wascarried out with respect to the radiation damage. The
mechanical strength of the samples was measured before andafter irradiation. The sample was irradiated with y -ray from
6 °Co and the total dose was 1.3 x 10 4 C I kg.
It has been
confrrmed that both samples endured the pressure of over 100kg I cm 2 and repetitive pressurization of 10000 times.
Investigation of the change in qualitySome of the rubber pipes for QB magnet which have beenused from the beginning of the accelerator operation could notendure the cooling water pressure of only 10 kgf I cm2 . Thefailures happened 6 times after all. The outside layer burst
lengthwise in about 10 em and the middle and the inside layers
in about Scm in all cases. Water flew out heavily at everytime. This phenomenon was a little different from the case ofQW4 magnet mentioned above.
Then we ordered the technical company to analyze new and-285-used rubber pipes in order to investigate the reason why thefailure happened. The analyses were carried out on thefollowing items.
Table 3. Items of the analyses

magnets and ordered the company to manufacture the improved
rubber pipes of which thickness of the inside layer is 3mm.
The replacement work of the 1024 rubber pipes was carriedout at the end of September for 5 days. There happened nofailure after the replacement for one year.
RUBBER PIPES OF THE POWER SUPPLIES

1) surface observation observation of surface condition withscanning electron microscope(SEM)
2)qualitative analysis X ray micro analysis(XAM)of elements
3)qualitative analysis spectrum analysisof the infrared ray absorptionof materials
Soxhlet extraction ( solvent : acetone )4)quantitative
determinationof the rubber admixture
It became clear that for the degraded rubber pipe each layer
seemed to be changed in quality on surface appearance and therubber admixture also to be decreased in quantity.
Investigation from the point of view of the structure
Up to here the degradation of the rubber pipes was
examined from a viewpoint of radiation damage and chemicalprocess. But finally it proved the design of the rubber pipe tobe insufficient.

Outline of the failure
For MR magnet system 72 power supplies which are cooledby pure water have been installed in 4 power supply stations.
The rubber pipe for water cooling has been adopted as
insulator against the ground .
In June, 1992 it happened the burst failures of the rubber
pipes twice at the same period of the magnet failures. But inthis case it has been considered that the failures were caused byquite different reason.
Investigation of the failure
Table 4. shows the specification of the rubber pipe. It also
consists of 3 layers for reinforcing.
It could not be explained that the rubber pipe could not endure
the water pressure of only 10 kgf I cmz with the condition of noradiation. Then the detail analysis same as the case of magnet
was carried out.
Table 4. Specification of the rubber pipe

Fig I. Change in diameter with water pressure

normal pressure
test pressure
minimum break-downpressure
minimum loadfor drawing fittingsworking temperature
outside layer
reinforcing layer
inside layer-10102030

Pressure ( kg! I em 2 )The thickness of the inside layer of the rubber pipes used forQA, QB and Qc magnets are 3mm, 1.75mm and 3mm
respectively. This difference affects the life of the rubber pipes
essentially. It looks like that the life of the rubber pipe for QB
magnet had been reduced extremely in accordance with thedegradation of the rubber and the vinylon fiber after long timeuse. To confirm this fact the pressurization test was carried out
for a new one and a degraded one. Fig 1. shows the result.
New one endured the pressure with 35 kgf I cm 2 for 10minutes.
Replacement work
On July end we decided to replace all rubber pipes for QB

18 kgf I cm 235 kgf /cm 272 kgf I cm 2135 kgf-40°C-93 oc
rubber formulated CR family( polychloroprene rubber )synthetic fiber braided ( rayon )rubber formulated NBR family( acrylonitrile butadiene rubber )Investigation of the change in quality
Technical company analyzed the new and used rubber pipes inregard to the items same as the magnet case. It became clearthat each layer seemed to be changed in quality on surface
appearance and the rubber admixture also to be decreased inquantity for the degraded rubber pipe.
Investigation of the deposit inside the rubber pipe
The brown colored deposit was confirmed on the surface of
inner layer by the observation of two burst rubber pipes. It
proved to be that this phenomenon was the decisive evidence ofthe failure at this time. Fig 2. shows the qualitative analysis of
the deposit. As can be seen the main component of the deposit
is Cu.
Mechanism of the deposit
For the power supply Cu metal has been used for watercooling fin of SCR, hollow conductor of transformer etc. The
mechanism of the dissolution of Cu metal into water and the-286-

deposit of the Cu oxide on the surface of rubber pipe were
estimated as Fig 3.

has been caused by the exchanging of S for Cu atoms in themolecular bond. And also it was found that the deposit could
be seen only on the rubber pipe supplied with DC voltage.

Fig 2. Qualitative analysis of the deposit
Fig 4. Appearance of the deposit@@@(f)@@(jjbcucu.

material for evaporating~_1t-~-I1

Cu + - 02Cu 2 +2+20H -Cu ( OH) 2

Cu is in existence as copper hydroxide in pure water of pH~

belowpH

Cu is in existence as Cu ion in the waterover pH( OH) 2 _ _ _ _.,..
Cu2Cu0

ffi

ffi

ffi

-

....----

-G

0

0

G 0

0

00

From the investigation described above it proved to be that itis impossible to use the NBR group rubbers to the water coolingsystem which uses Cu metal for conductor.
In addition, quite different phenomenon was found. ForB
magnet power supply the ground fault failures through Cu
oxide deposit happened frequently a little before the burst
failures.
Replacement work
We decided to replace all the rubber pipes which weresupplied with DC voltage at both ends. The EPDM rubber pipe
was adopted at this time by the reason mentioned above.
In case of power supply the rubber pipe has been made use of
only by putting into the nipple on main water pipe. By cutting
into required length from the rubber pipe roll the 80 rubber
pipes for B, QF and QD magnet power supplies and 1080 forother small-sized Q magnet power supplies were replaced.
The replacement work was carried out in the middle ofSeptember for 13 days. There happened no failure after thiswork.

Dissolution of Cu metal into water

Cu + 20H+ -----.../

ffi ffi ffi ffi ffi ffi

Fig 3. Dissolution and deposit of the Cu-8-E)+ -8-

10.230 C~eV)

5.120

CONCLUSION

Cu 0 + HzO + Q cal
Cu 2 0 + (0)Cu is in existence in the water as copper oxide ( Cuz 0 ) orcuprous oxide ( Cu 0).
The molecules of the copper oxide and the cuprous oxideand the inner layer of the rubber pipe are charged, so the Cu
oxide will be deposited on the surface of the rubber pipe by theelectrostatic force. The condition of the charging depends on
pH, flow velocity and temperature of water, and electricfield. Fig 4. shows the appearance of the deposit of Cu oxide.
It is said to be that the degradation of the NBR group rubbers

It will be necessary to pay attention to the following mattersat the time of designing magnet or magnet power supply.
1) The rubber pipes of NBR family cannot be adopted if there
was a possibility that Cu ion dissolves into the cooling water.
2) In generally the degradation speed of rubber pipe will
be enhanced under the environment of water. Thus in timeof designing rubber pipe it must be taken into accountto make the thickness of this .Jarge enough.
3) Even if water resistant materials is used, there will be apossibility of ground fault failure caused by the deposit ofCu oxide. Therefore the periodical maintenance of thecooling water system should be carried out.

-287-