Ornl tm 1023 by The "E" Generation

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ORNL- TM- 1023

TUBE PLUGGING IN THE MOLTEN-SALT REACTOR EXPERIMENT -. ._-_

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PRIMARY HEAT EXCHANGER ,. . . _ ____ ~ -_ . -__

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R. G. Donnelly

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ORNL- 'I'M- 1023

C o n t r a c t No.

W-7405-eng-26

METALS AND CERAMICS D M S I O N

TUBE PLUGGING I N THE MOLTEN-SALT REACTOR EXPERIMENT PRIMARY HEAT EXCHANGER R. G. Donnelly

FEBRUARY 1965

OAK RIDGE NATIONAL LABORATORY O a k R i d g e , Tennessee

operated by UNION CARBIIE CORPORATION f o r the U. S. ATOMIC ENERGY COMMISSION

1 TUBE PLUGGING IN T'fE MOLTEN-SALT REACTOR EXPERIMENT PRIMARY HEAT EXCHANGE8 R. G. Donnelly

ABSTRACT

I n order t o reduce t h e pressure drop through the shell side of t h e Molten-Salt Reactor Experiment primary heat exchanger, it was decided t o remove four of t h e outer U-tubes. This required sealing t h e eight tube stubs produced. Aplug design and seal welding procedure were developed t o assure a high-integrity s e a l between the molten f i e 1 salt on t h e shell side and t h e coolant salt on t h e tube side of t h e heat exchanger. The plugs were made t o have a s l i g h t interference f i t (0.0000 t o 0.0002 i n . ) with t h e tubes and The plug material was were machined f o r edge-welding. INOR-8as was the e n t i r e heat exchanger. The procedure f o r making t h e seals w a s t o manually weld the tube end t o t h e plug with a gas tungsten-arc torch. The welding conditions were adjusted t o provide weld metal penet r a t i o n equivalent t o a t l e a s t the thickness of t h e tube w a l l . Visual, dye-penetrant, and radiographic examinations of t h e w e l d s gave every indication t h a t high-integrity welds had been made t h a t would successfully i s o l a t e t h e f u e l s a l t from the coolant salt during t h e planned operation of the heat exchanger.

INTROlXJCTION

During p r e i n s t a l l a t i o n flow t e s t i n g of the primary heat exchanger f o r t h e MoltenSalt Reac

eriment (MSRE), t h e pressure drop through

the s h e l l side w a s found

e s i g n i f i c a n t l y greater than w a s desired

and reqyired modificatio

e heat exchanger i s of the conventional

U-tube design (See Fig. wall.

All 326 tube ends

tubes being 0.50-in.

OD X 0.042-in.

oined t o a 17-in. dim X1.50-in.

thick

tube sheet by welding and back brazing. The containment material i s t h e commercially available alloy, IN OR-^

'R. G. Donnelly and G. M. Slaughter, "Fabrication of t h e Molten-Salt Reactor Ecperiment Heat Exchanger Core," Welding J., 43(2), llS124, (1964)

2 UKUUCILO Q N L U Q O SZO3SRZ

FUEL INLET

THERMAL-BARRIER ?LATE TUBE SHEET

COOLANT INLET

COOLANT OUTLET CULL OUTLET

Fig. 1. Molten-Salt Reactor Experiment Primary Heat Exchanger.

(mi-17 Mo-7 Cr-4 Fe, w t 6). This alloy is a nonage-hardenable highstrength material which possesses excellent corrosion resistance to the molten salts and good oxidation resistance. It also exhibits good general weldability. However, it has shown a tendency toward microfissuring under certain welding conditions. Thus, the welding procedure and joint design were more critical than usual.

*W. D. Manly, -et al. pp.164-79 in Progress in Nuclear Energy, Series IV, Vol. 2 Technology, mineering and Safety, Pergamon Press, London,

1960. 3G. M. Slaughter, P. Patriarca, and R. E. Clausing, Welding J. = 38(10), 393d006 (1959) â&#x20AC;&#x2DC;MSRP Semiann. Progr. Rept. July 31, 1964, ORNL-3708, p. 363.

3 The method approved f o r reducing t h e pressure drop was t o remove t h e four outer U-tubes which were s i t u a t e d d i r e c t l y at the mouth o f + t h eshells i d e i n l e t and o u t l e t nozzles.

After removal of the shell, the four tubes This was accomplished by

were cut, leaving eight stubs t o be plugged. pressing in INOR-8plugs and s e a l welding.

The development of procedures, qualification of t h e welder, and t h e a c t u a l tube plugging operation are described.

DEVELOPMENTAL WORK J o i n t Design Due t o t h e low-pressure d i f f e r e n t i a l (50 p s i ) between the tube and s h e l l sides of t h e heat exchanger, t h e plug was not required t o have great strengthj however, a leak-tight j o i n t was e s s e n t i a l .

Therefore,

with these f a c t s i n mind and taXing i n t o account t h e proximity of t h e

adjacent U-tubes, an edge-type weld preparation was made on the plugs

as shown i n Fig. 2. UNCLASSIFIED ORNL- DWG 64 11563

/WELD

-TUBE

Fig. 2.

WALL

Schematic of Tube Plugging Design.

4 Each plug was positioned flush with the tube end.

It was f e l t t h a t a

qualified welder with a s m a l l gas tungsten-arc torch could more e a s i l y

make a high-quality weld on this type of j o i n t than on any other.

Since

the edge-type weld design also readily allows the tube end t o be joined t o a member of similar thickness, adequate j o i n t penetration i s more e a s i l y assured. Both the scpare-edge design and beveled-edge design were investigated. The thickness of the l i p on the plug was also varied; the amounts being 1, 1 1/4, and 1 1/2 times the tube-wall thickness.

In addition, j o i n t s

were welded by single-pass fusion, single pass with f i l l e r , and by a combination of f'usion and f i l l e r passes.

In the end, no combination

I V

proved b e t t e r than the square-edge design with a l i p thickness equal t o the tube-wall thickness welded i n one fusion pass.

However, a l i p thick-

ness of 1 1/4T was ultimately chosen t o assure a minimum of 1T weld penetration i n any section of the weld. The plugs were tapered and machined f o r each individual tube t o provide a s l i g h t interference f i t (Fig. 3 ) .

An interference of 0.0005-in.

was found t o cause d i f f i c u l t y i n f i t t i n g i n some cases, so a value of +o*0002 in. was chosen. -0.OOO0-

With such a t i g h t f i t none of the 30 samples

examined metallographically exhibited any indication of root cracking. Welding Procedures With the j o i n t and plug designs chosen, the welding parameters of

arc current, t r a v e l speed, and electrode orientation were varied i n an e f f o r t t o determine t h e optimum combination.

In addition, a copper c h i l l

was f i t t e d t o the tubes a t a distance of about 0.070 i n . from the top of the Joint.

It was f e l t that this would tend t o even out t h e thermal

gradients between the tube and plug. Welding current was varied from 30 t o 45 amps, and time f o r one revolution w a s varied from 40 t o 77 sec.

An overlap of 3/16 t o 1/4-in.

was made at f u l l amperage, and a foot-operated current tapering device was used a t the beginning and end of each weld t o eliminate weld craters.

The conditions giving the best penetration and weld configuration were: '

Electrode material:

W + 2$ thoria

Electrode diameter:

1/16-in.

UNCLASSIFIED ORNL-DWG 64-1!562

I I b-NOTE

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DIMENSIONS NOTE i: MATERIAL:

Fig.

ARE

IN fNCHES

MAXIMUM

TUBE

INOR-B

ROD

I’. D. :;:$gg$

Tube Plug for MSRE Heat Exchanger.

I I

I n e r t gas:

argon ( 99.99$ purity)

Gas flow rate:

17 cfh

Welding current: Welding speed:

(34 W a m D 40 t o 55 secljoint

The position of the electrode with respect t o the j o i n t was found t o have an e f f e c t on the configuration and, therefore, the effective , penetration of the weld.

The best results were obtained by holding the

electrode t i p on the outside edge of the tube.

This required t h a t the

welder touch the adjacent tubes with the e l e c t r i c a l l y insulated p a r t s of

A photomicrograph of a typical j o i n t welded under these conditions i s presented in.Fig. 4.

the torch.

Fig. 4.

Photomicrograph of a Qualification Test Sample.

40X.

...

WELDER QUALIFICATION The welder was qualified on j o i n t s i n a setup which simulated the configuration of the actual heat exchanger. %'he mockup i s shown i n Fig. 5.

The welder had been previously qualified f o r gas tungsten-arc

welding of INOR-8 i n accordance with ORNL Operator*s Qualification Test

QTS-25. The qyalification welds were required t o have the following: (1)uni-

form weld contour with no visual evidence of cracking o r porosity, (2) no positive dye-penetrant indications, (3) weld penetration of a t l e a s t one times the tube-wall thickness as evidenced by metallographic examination, and (4)no porosity of a s i z e greater than 1% of the tube-wall thickness when radiographed i n accordance with paragraph UW-51, Section 8, ASME Boiler and Pressure Vessel Code. All requirements were met, and no

porosity of any s i z e was revealed.

Fig. 5.

Mockup of Heat =changer Used i n Welder's Qualification Test.

8 Prior t o making the welds on the heat exchanger, the welder was also ,

required t o make one o r more sample welds f o r visual examination as required by the welding inspector.

THE

PLUGGING OPERATION

The first item i n the procedure was t o remove the four outer U-tubes. Heavy metal bars were clamped t o t h e four tubes t o a c t as guides f o r the pneumatically operated abrasive wheel t h a t was used f o r the cutting Metal plates were also used between the tubes being cut and

operation.

adjacent tubes t o prevent any damage by the cutting wheel. were made 1 1/8 in. f r o m the b a r r i e r plate.

The cuts

This allowed sufficient room

f o r t h e c h i l l block and also f o r repreparation of a tube end should this be necessary

I n addition t o the four U-tubes, four adjacent b a f f l e support rods were a l s o removed t o provide access f o r the welding torch. These rods were not replaced. The resultant eight tube stubs were squared off, deburred, and cleaned of a l l oxides f o r a t l e a s t 1 in. from t h e i r ends.

The inside

diameter of each tube end was then measured, and the maximum reading f o r each recorded.

The r e s u l t s are l i s t e d i n Table 1 along with the plug

diameters f o r t h e i r respective tubes.

It w i l l be noted that the plug

f o r tube "E" was 0.0002 in. greater than the z : s o - i n .

range desired.

Nevertheless, the plug was f i t t e d without difficulty. Immediately before f i t t i n g a plug, both the tube and the plug were degreased with acetone. cleaned punch. tube end.

The plug was then set i n t o the tube stub with a

A shoulder on the punch stopped the plug flush with the

After f i t t i n g the c h i l l block, t h e welding sequence discussed

previously was followed and the j o i n t visually inspected.

The process

w a s repeated f o r each tube. Visual examination revealed two welds that had areas of questionable penetration.

After demonstrating repair operations on sample welds, the

welder went over the two areas a t fill amperage t o assure sufficient penetration.

t I

9 Table 1. Tube Designation

Tube Inside Diameter Maximum (in. 1

A B c

f 1

.*i

Tube and Plug Measurements

D E

0.4151 0.4157 0.4176 0.4133 0.4142

F G H

0.4162 0.4156 0.4134

Plug Outside Diameter (in. 1 0.4153 I

0.4157 0.4176 0.4134 o.4uda 0.4162 0.4156 0.4135

a0.0002 in.

oversize.

All

welds were then inspected by dye-penetrant and radiographic were revealed. methods. No imperfections A photograph of four of the sealed tubes is presented in Fig. 6.. CONCLUSIONS' As a result of this work, it is felt that the tube plugging procedures and joint design developed are consistent with the operating

,requirements of the heat exchanger. The use of these procedures, coupled with a specially qualified welder, has resulted in sound welded joints which give every indication of successfully sealing the molten fuel salt from the coolant salt during the planned operation

of the heat exchanger.

ACKNOWLEDGMENT The author would like to thank the following people who-contributed to this work and whose personal interest in high-quality workmanship are appreciated:' R. G. Shoos&r of the Welding and Brazing'Group, Metals and ~Ceramics Division; IT. R. Housley and J. W. Hunley of the Plant and Equipment Division, Welding Inspection Group3 and W. H. Brown, welder with the Plant and Equipment Division, Research Services Group. The metallo-

bd i

1: .

graphic assistance of E. R. Boyd of the Metals Metallography Group is also acknowledged.

and Ceramics Division's

Fig. 6. (see i n s e t ) .

Four of the Sealed Tubes Inverted from Welding Position

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24. 25-34. 35. 36.

Central Research L i b r a q Reactor Division Library ORmL Y-12 Technical Library Document Reference Section Laboratory Records Department Laboratory Records, ORNL RC ORNL Patent Office G. M. Adamson E. S . Bettis G. E. Boyd R. B. Briggs K. V. Cook J. E. Cunningham R. G. Donnelly C. W. Fox J. H Frye, Jr.

54. 55-56 57. 58. 59. 60. 61-75.

C. M. Adams, Jr., Massachusetts I n s t i t u t e of Technology D. F. Cope, AFC, Oak Ridge Operations Office J. L. Gregg, Bard H a l l , Cornel1 University J. Simmons, AEC, Washington E. E. Stansbury, University of Tennessee Research and Development Mvision, AEC,ORO Division of Technical Information Extension

1-3. 4.

7-16. 17.

18.

f 1

19. 20. 21. 22. 23.

37.

38. 39-41. 42. 43.

44.

45 46. 47. 48. 49. 50. 51. 52. 53.

W. R. Gall R. G. Gilliland M. R. Hill T. R. Housley H. G. MacPherson W. B. McDonald W. R. Martin R. W. McClung P. Patriarca G. M. Slaughter A. Taboada J. R. Tallackson W. C. Thurber A. M. Weinberg J. H. Westsik