ML20213F921

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Collapse Tests on Intentionally Damaged Alloy 600 Once- Through Steam Generator Tubing
ML20213F921
Person / Time
Site: Arkansas Nuclear Entergy icon.png
Issue date: 04/20/1976
From:
BABCOCK & WILCOX CO.
To:
Shared Package
ML20213F823 List:
References
LR:76:2341-74:1, NUDOCS 8611170248
Download: ML20213F921 (17)
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CbCOCk & MX .,,, ,, = ,,m . c...., ..o w .saei i I D. F. LEVSTEK - MPGD, LYNCH 8URG W {.H. MEN - CHEMISTRY & CORROSION, ARC e..,,.,,,,

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obj. COLLAPSE TESTS ON INTENTIONALLY DAMAGED ALLOY 600 Sets OTSG TUBING APRIL 20,1976 g.~.....-...-.-, ,

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SUP94ARY A test progmm on the effect of a lose of coolant accident (LDCA) on D inte ::ic'ully d2uged Alloy FCC steam generator tubing was carried out at the {

Q A Miance cesearch Center. *he progrcr- consisted of a serice of ocllapse tests

'o i r. refrechel OTsa :uality va:er at 600'T ard pressures betveen 2000 and i

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Distribution (COMPANY LIMITED) This infonnation is freely available to all Company personnel. Written approval by sponsoring unit's R&D coordinator is required only if release outside of the Company is requested.

r1 F.J. Pocock

. P.S. Ayres 0 M.J. Bell - NPGO, Lynchburg M.J. Mravich/W.S. Leedy

%s y R.U. Blaser J.P. Rowe E.E. Coulter - NED, Akron P.E. Sensmeier

' H.F. Cobel - MPGO, Lynchburg T.S. Sprague/L.E. Spry - NED, Barberton p H.4. Domian R.M. Douglass - Mt. Vernon G.J. Theus G.F. Tisinat - Beaver Falls g Chemistry & Corrosion Files (3) g G.N. Ensunuel - Mt. Vernon 0.W. Koch /N.L. Evanchan - NED, Akron Contract Control D J. A. Manzi/E.M. Oorsey B.N. Mcdonald - NPGO, Lynchburg Corporate Information Services Anr tihrarv (3)

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% R.C. Ritschard/J.V. Monter J d. Musat 8611170248 861031 PDR ADOCK 05000313 P PDR

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l B&W makes no werranty or representation, expressed or implied:

e with respect to the suuracy, completeness, or usefulness of the information contained in this report e that the use of any information, apperatus, method, or process disclosed in this report may not infringe privately owned righti B&W assumes no liat>Isty with respect to the use of, or for damages resulting from the use of.

e any informetion, apparates. method, or process disclosad ir.

this report 1 e experimental apparatus furnished with this report.

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Page 2 Babcock & Wilcox LR:76:2341-74:1 s

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1. INTRODUCTION j Abnormal operation of a once-through steam generator (OTSG) may subject its Alloy 600 tubing to a variety of potentially da sging events. Movement between the support plates and tubes my result in thin.!na of the t@e wall due to mechanical wear. Water chemistry upsets may lead to intergranular attack, intergranular stress corrosion cracking, or wastage attack. Should any of these events occur, it could pose a safety related question if a loss of coolant accident (LOCA) were to subsequertly occur. The question would relate to how much damge a tube can endure and still perform satisfactorily in case cf a LOCA.

5hould a LOCA incident occur, the damaged tubes would have to withstand the entire secondary side pressure (approximately 1000 psi) without collapsing.

If tube collapse did occur, the tube wall might rupture and secordary water could enter the primary system and perhaps overload the containment building's pressure capacity. Therefore, there is a need to ascertain how much external pressure a daraged tube can withstand before collapsing and rupturino. In order to determine the extent of " allowable" tube damage, a test program was conducted wherein intentionally damaged Alloy 600 OTSG tubes were subjected to various collapse pressures. The specific objective of the test program was to l determine whether or not tubes damaged to 50% of their wall thickness could I withstand a LOCA incident.

?. TE3T PROGRAM 1

2.1 Material The material used was Alloy 600 OTSG tubing, Heat M5442, manufactured by the Tubular Products Division of the Babcock & t!!!cox Company. All Tubing 1

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' Pas stress relieved, 1150'F/18 hrs, prior to testing. The actual dimensions of this tuMng are 0.d28" 00 x 0.038" wall. The analysis is given in Table 1.

Table 1 Analysis of Heat M5442 v

C .051 Cr 15.81 Fe 8.92 Mn .37 Ni 74.01 Mg .037 5 .0063 Mo .07 Al .28 B .0018 Cu .02 Ti .25

,. Si .13 Co .045 Pb <.005 2.E ' Specimens Duplicate test specimens,18" long, were made of each defect geor etry.

The tubes were sealed at' bc,th ends by welding in a plug of the same material.

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Defects were placed in thi middliof each tubular sr,ecimen, w*th the exception of two undamaged tubes used as comparison spetjmens.

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2.3 Defect Depth The objective of the program is to assure satisfactory tube perforrance in case of a LOCA incident with tubes having incurred damage such that only 50% of their wall ranained. Tubes with a 50% defect depth were not expected to collapse with of.ly' LOC 5 pressures applied, f.e.1000 psi. Therefore, tubes with defect depths greater than 50% of the wall were tested and pressures higher thar.1000 psi were imposed to estaolish tN relationship of defect depth and shape with collapse pressure. Tubes with defect depths less than 50% of the remaining wall w(re also tested to traplete the test array.

The defe:t depths used for each defect gecmetry were:

, 1)' 1001(0.038") of tube wall ree.sining (no defect)

- 2) 75% (0.0285") of tube well retaining P

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Babcock & Wilcom L R:76:2341-74:1 Page 4

3) 50% (0.019") of tube wall remaining
4) 30%(0.0114") of tube wall remaining.

2.4 Defect Geometry Two specimens of each defect geometry / defect depth combination of interest were tested. The various defect types are described and illustrated below.

e Longitudinal Slit A longitudint,1 groove. 0.010" wide and I" long, was machined in the outside surface of the tube with a milling cutter. This defect simulated a

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longitudinal crack in the tube wall.

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s Circumferential Slit A slit defect groove. 0.010" wide, and extending around 12G' of the circum'erence was machined in the outside surface of the tube with a milling cutter. This defect simulated a circumferential crack in the tube ws11.

e Circumferential Thinning A 360' area of uniform thinning 0.5" long was machiied on the outside surf at e of the tube. Tnis defect simulated an area of uniform t. nning of the tube wall.

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Babcock & Wilcox LR:76:2341-74:1 Page 5 e Flat Defect A flat spot. 0.75" long, was introduced on the tube wall by two techniques -

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machining and by electrochemical (sulfuric acid - glycerine ritture) machining

- of the metal. These defects sirnulated areas thinned by mechanical wear (machined) or by chemical attack (electrocheHcal machining). Chemical attack did not result in significant intergranular penetrations of the tube wall as can be seen in Figure 1.

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Figure 1. Appearance of Tube Surface After Removal l

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2.5 Test Conditions Each test was conductej for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> at 600*F and the pressure was varied, in 500 psi increments, between 2000 psi and 4000 psi. All tests were conducted in a refreshed autoclave using nonel GTSG feedwater (Table 2).

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I Babcock & WNees LR:76:2341-74:1 Peee 6 Table 2. Test Solution

- pH 9 25'C 9.3-9.5(M4) 3 Conductivity 4-10 umhos/cm j 0xygen 0 (i.e. residual hydrazine) l Iron <5 ppb Temperature 600'F(316'C)

Flowrate 0.5 gal /hr (1.9 titers /hr)

Prior to testing, the diameter of each specimen was measured at three points on the circurnference at the site of the defect. After this, the specimens were installeo in a carbon steel holder (Figure 2). The assew6ly was placed in the autoclave and the autoclave was pressurized to the desired level and then heated with water f'owing through it. Pressure was maintained by a mechanical back pressure regulator. Water was supplied to the autoclave by means of a high pressure mechanical pump. After each test, all specimens were remeasured at the same locations on the circunference. If any evidence of flattening was observed, the specimen was removed and regarded as failed. In most cases, failed specimens collapsed and there was little doubt whether failure occurred.

l When measurements were completed, the unfailed tubes were placed back in test.

Failed tubes were testeo for rupture by removing the cap on one end, imersing the tube in water and pressurizing the inside with helium. Bubbles would form at the site of a through-wall failure.

3. RESULTS & OISCUSSION Results of the tests are presented by test pressure.

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,4 Figure 2. Collapse Specimen Holder With One Test Specimen Installed

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o Figure 3. Appearance of Fracture in Failed Tube 3000 psi 3500 psi

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j and Figure 4 suwvnarize the results of the test program, and Figures 5 through fs show tubes after failure.

From the results preser.ted in Table 3 and shown in Figure 4, the follwing surrary staternents can be made:

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Babcock & Wilcos LR:76:2341-74:1 Page 10 Table 3. Summary of Results of Collapse Test. 628" 00 m .038" Wall.

Alloy 600 Tubing Temperature: 600*F. Circulating OTSG Feedwater Time: 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> at each pressure. Maximum pressure 4000 psi Type of Defect Circtsferential Slit 120' ,

Longitudinal Slit Circumferential. 360' l Flat (Machined) l L

Flat (Chemical)

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4. CONCLUSIONS i The results of collapse tests on intentionally damaged Alloy 600 OTSG tubing allows us to conclude that:

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5. REC 0m EN W IONS This test has demonstrated only the effect of pressure (loss of primary coolant) on the collapse properties of intentionally damaged Alloy 600 OT56 tubing. The burst properties of similar tubing were not investigated. In order

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Babceedt & h LR:76:2M1-74:1 Paes 17 1 1

l to complete the study of the behavior of this material under adverse operations, we recommend the initiation of such a progrars. The burst properties of Alley 800 tubing with the same defect geometries as the collapse specimens, at the same pressure and temperature, should be determined. A program to detemine the tensile properties of damaged tubing at room temperature and at 600*F is also recomended.

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"M. & WRces LR:76:2341-74:1 Paae 17 to complete the study of the behavior of this material under adverse operations, we recomend the initiation of such a program. The burst properties et' Alley 400 tubing with the same defect geometries as the collapse speciesns, at the same pressure and terature, should be deteroined. A program to detemine the tensile properties of damaged tubing at room tamperature and at 600*F is also recomended b vm ,

R. H. Emanuelson/G. J. Theus

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