ML19274D520
| ML19274D520 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 02/07/1979 |
| From: | KANSAS GAS & ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML19274D521 | List: |
| References | |
| NUDOCS 7902120222 | |
| Download: ML19274D520 (14) | |
Text
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. '.s FINAL FEFORT ON SPOT WELDED STRUTS FOR SNUPPS PROJECTS TABLE OF CONTENTS SECTIO!{
TlTLE PAGE 1.0 Introduction 1
2.0 Material Description 2
3.0 Material deficiency and its Safety Implication 2
4.0 Technical Evaluation and Criteria 3
5.0 Test Program at Jobsites 4
6.0 Additional Plan of Action 4
7.0 Test Program at Unistrut Corporation 5
8.0 Corrective Measures 7
9.0 Conclusions 8
TABLES:
1.
Test Results of Callaway and Wolf Creek Jobsites 9
s 2.
Test Specimen Details 10 3.
Shear Load Test Sur: nary 11 4.
Retreat of Specimen 12 SKETCll:
13 1.
Test Set-Up 790212& M
1.0 I r;T RODUCTION s
In accordance with the requirementt, of 10CFR 50.55 (e), this report is prepared to provide a final sum:r.ary of the deficiency in spot resistance welding of electrical raceway support material, pur-chased under Specification No 10466-E-037.
In July 1978, SNUPPS Project was advised of a problem related to inadequate spot resistance welding on the strut supplied by Uni-strut to several other projects, where the adjoining channels were separating during fabrication of supports. No such failure was reported on either of SfIUPPS jobsites.
Immediately, tests were initiated at both SNUPPS sites. A total of 76 randomly selected samples from different strut types were subjected to a shear test to verify thc weld strength. No failure was reported.
The specification was revised to include shear test for any new material purchased as a precaution. Additionally, 380 randomly selected samples from both sites were tested at Unistrut test laboratory to obtain more data.
Only one Unistrut Part No P-5501, Coil No 7J-4661 from Wolf Creek site, was found unsatis-factory.
Immediately, actions were taken to remove this strut from the site.
During the test performed in 1978 with specimens from Unistrut P-1001, Coil No 7X-4444, one weld sheared below 1200 pounds, the established lower strength requirement. Since this was the only instance in which this material did not meet minimum require-ments, this instance was considered to be an isolated case.
Page 1
On January 3, 1979, during on-site processing one section of P-1001 Unistrut of Coil No 7X-4444, 55 -7/8" long, containing 23 spot welds was found to have 21 defective spot welds. This Unistrut had separated at each defective spot weld without ex-ternally applied stress. As a result, all P-1001 Unistrut at the jobsite was inspected and material of Coil No 7X-4444 was identified.
2.0 MATERIAL DESCRIPTION Basic strut channels are roll formed from hot dipped galvanized
- 12 gauge, 0.105 inch thick strip steel. These channels are connected to each other in various configurations, c"
=9 back-to-back, back-to-side, or side-to-side, by spot resistance welding. This material is purchased from Unistrut Corporation, Wayne, Michigan, as standard catalog items under the Specificat an lO466-E-037, used in field fabricated supports for electrical raceways.
3.0 MATERIAL DEFICIENCY AND SAFETY IMPLICATION.c The strut is used in the electrical raceway support system design.
The connection provided by spot welds between the strut sections is relied upon to maintain the integrity of the built-up section to carry the postulated loads, within the design margins.
- Thus, inadequatt 'usion at the spot welding may result in inadequate strength and may adversely affect the safe operation of the plant, under severe loading conditions.
After reviewing the nature of the deficiency experienced on other projects, the following was concluded:
The deficiency was related to spot welding technique and/or a.
procedure.
Page 2
The quality of the spot welding can r.ot be evaluated wit hout b.
actual t est to verify the strengt h of the weld, Dest ructive shear t est will provide the failure load data c.
for t he weld, and will positively verify the soundness of the sopt weld.
4.0 TECifNICAL EVALUATION AND CRITERIA Based on t.he "Reconnended Practices for Feuistance Welding",
AWS C1.1, by American Weldinj Society, AISI Specification for M <tructural Members, Part I, the Design of Cold-Formed Ste Section 4, specifies allewable shear strength per spot weld to be equal to 1.65 kips, with a factor of safety of 2.5 for 0.109 inch thickness.
11igh factor of safety is specified to account for the deliendence of the quality of spot weld on many variables such ar tips of electrodes, pressure, voltage, current, presence of im-purit ies, finish of the material, maintenance of the equipment.
The connection provided by spot. welds between the st rut sections is relied upon to maintain the integrity of the built up sections.
The calculated shear in a spot weld in a member depends upon variables such as loading, sectional properties, and conditions, use of strut as beam, brace, column or tie, etc.
Factor of safety used for the bedding stresses in the struts is 1.65 in the design of the supports.
.nerefore, it is reasonable to consider a shear value different than that specified by AWS.
Conservative weld strength requirement for SNUPPS Project is calculated to be a maximum of 1,200 lbs only. Therefore, for the analysis of the test data, failure load of 1,200 lbs or below is considered in-adequate.
Page 3
It was also decided that when failure load is below 3,200 lbs for a test specimen, two adjacent welds shall be tested to provide additional data.
A value of 3,200 lbs failure load is chosen as a conservative design base which includes safety factor of 2.G+.
5.0 TEST PROGRAM AT JOBSITES,- (Callaway and Wolf Creek) 1978 5.1 Testing Forncy Compressive Testing Machine (which is used for concrete a.
testing) with specially f abricated fixtures was selected to perform this test, Samples were selected at random from every strut Jot received b.
for different purchase orders.
Destructive shear test was performed and failure loads were c.
recorded.
d.
Summary of the test data is tabulated in Table No 1.
5.2 Review of the Test Data Out of 76 samples tested, only one weld was below 3,200 lbs, failure load being 1,600 lbs with adjacent weld at 3,400 lbs.
Including the above weld, there were 3 welds between 3,400-4,000 lbs, two at 4,000 lbs and 71 were above 4,000 lbs.
Highest value was 9,000 lbs.
5.3 Conclusion of Initial Test This data did not indicate any problems with struts at SNUPPS sites, and provided reasonabic assurance about the adequate quality of spot welds.
In addition, the specification was revised to require additional testing for future shipments.
6.0 ADDITIONAL PLAN OF ACTION 1978 The following plan of action was decided in the meeting between Unistrut, SNUPPS and Bechtel on August 17, 1978:
Unistrut indicated that starting in 1978, all materials a.
Page 4
fabricated and deliu red to the SNUPPS jobsites had been rubjected to pull tests, the results of which were traceable to individual coils of materials delivered. This data was reviewed and considered acceptable, subject to final Bechtel audit.
(This data was reviewed at Unistrut by a Bechtel representative on October 17, 1978, and was considsred accept-able.)
b.
Representative sampics from 1976-1977 strut material shall be subjected to shear test, as the pull test data was not available or trace &ble.
Materials to be shipped in the future shall be required to c.
have shear test, per revised specification.
7.0 TEST PkOGRAM AT UNISTRUT CORP., WAYNE. M'CHIGAN 1978 7.1 Criteria Basic criteria was set per Paragraph 4.
7.2 Sample s Quantity of samples was based on one weld per 100 feet of strut.
An ef fort was made to select the samples from all dif ferent coil numbers previously delivered to Callaway and Wolf Creek jobsites.
All sampics were taken from stock, fabrication shop or scrap pile.
Table No 2 lists numbers of samples from each site, by strut type and number of coils.
3" long test specimens (380 total) were prepared and idnetified by Unistrut QA Department.
7.3 Testing Shear tests were performed using compressive shear test set up per Sketch No 1.
The tests were witnessed by a Bechtel representative.
7.4 Review of Test Data Summary of the test data is tabulated in Table No 3.
352/380 Page 5
specimens exceeded 3,200 lbs shear load.
An additional 15 specimens had shear loads between 2,400-3,200 lbs.
An additional 10 specimens had shear loads between 1,200-2,400 lbs.
Only 3 specimens were below 1,200 lbs, which were considered inadequate.
Two of these were from the sama Coil No 7J-4661, Unistrut P-5501.
These welds failed at sawcut, but three other sampics from the same coil were above 4,000 lbs.
One specimen below 1,200 lbs, was from Coil No 7X-4444, Unistrut P-1001.
There was a total of 15 samples from this coil, from which only one was below 1,200 lbs.,
two were above 2,400 lbs, and twelve were above 3,200 lbs.
There were 15 samples from Coil No 7K-4444 (same coil as 7X-4444, but different operator), 14 were above 3,200 lbs, and only one was at 2,350 lbs.
Additional data for the welds adjaccat to the specimen with a failure load of below 3,200 lbs, are tabulated in Table No 4.
Average shear load (average of the original specimen and two adjacent welds), was higher than that of the original specimen.
Two exceeded 3,200 lbs, one of which was from Coil No 7K-4444.
i 7_ 5 Statistical Analysis The test data was grouped according to the welding machine wh.un produces a given shape. Statistical analyses were per-formed on each saml le to include computation of sample stat-istics (e.g. mean and standard deviation), plotting histograms, The and fitting probability de:.sity functions to the data.
factor of safety against failure, computed as, Minimum specified weld strength _
Factor of safety
=
Maximum design load Page 6
was greater than 2 for all camples; which is greater than the factor of safety for the strut material of 1.65.
The minimum specified weld strength was determined for a 90% confidence level; i.e. 10%
failures (minimum specified weld strength) in the lower tail of the probability density function.
7.6 Conclusion of Shear Tests at Unistrut Based on the above, one Coil No 7J-4661, Unistrut P-5501 at Wolf Creek Site, was considered inadequate. All o.her pre-1978 strut material exceeds the design requirement; failure in Coil No 7X-4444 is considere,t to be an isolated case.
Based on the defective piece of P-1001 material from Coil No 7X-4444 found on January 3, 1979 and the previous failure of one samplo of P-1001 material of Coil No 7X-4444, as cited in this report, P-lool Unistrut from Coil No 7X-4444 is considered to be inadequm.e.
8.0 CORRECTIVE MEASURES Specification No 10460-E-037 has been revised to include a.
additional testing of the spot weld at the manufacturing plant.
Documentation is required to be shipped with the strut.
b.
Unistrut P-5501 Coil No 7J-4661 has been removed from the Wolf Creek jobsite and will be replaced with acceptable material.
Unistrut P-1001 of Coil No 7X-4444 will be removed from c.
the Wolf Creek jobsite and will be replaced with acceptable material.
Page 7
9.0 CONCLUSICi;S The problem described in t his report was the result of:
Inadequate t est program prior to 1978 by Unistrut to verify a.
une siv t neld.
the strengtn vi b.
Inadequate maintenance cf welding equipment by Unistrut.
Supplier's actions including the added Quality Assurance and test programs per revised specifications, will provide adequate assurance of ef fectively precluding reoccurrence cf this problem in the future.
Page 8
Tahle No. 1
- Shear Load Test Su;. nary for Callaway and Wolf Creek Jobsites (1978)
A s.)
Unistrut No. Of Part No.
Specieen
( 1,200
<,2,400
< 3,200
> 3,200 P-1001 Callaway 60 60 Wolf Creek 8
1 (A) TOTAL 68 1
67 P-5501 Callasay 0
0 Wolf Creck 4
4 (B) TOTAL 4
4 P-5001 Callaway 0
0 Wolf Creek 4
4 (C) TOTAL 4
TOTAL (A+B+C) 76 1*
75 Note:
- l.
When adjacent veld was subjected to shear test, it exceeded 3,200 lbs.
2.
At Callaway, minimum and maximum shear loads were 4,000 lbs.
and 9,000 lbs., respectively.
3.
At Wolf Creek, minimum and caximum shear loads were 3,400 lbs. and 7,200 lbs., respectively.
Page 9
Table No. 2 Test Specimen Details:
(1978)
UNION - (CALLAWAY)
KANSAS - (WOLF CREEK)
Unistrut Total Total No.
Total No. Of No. Of Total No. Of No. Of Part No.
Quantity O f. Spec imen Quantity Specimen Coils Quantity Specimen Coils P-1001 20,000 216 10,000 91 7
10,000 125 8
P-5501 8,000 68 2,000 12 5
6,000 56 6
P-5001 9,500 96 3,500 23 2
6,000 73 29 TOTAL 37,500 380 15,500 126 14 22,000 254 43 o.
I Note =; (1) Coil riumbers selected for the sample at Callaway were different from those at Wolf Creek.
(2) All the samples were randomly taken from the respective coil number and Unistrut part number.
(3) P-1001, 20 foot long sections were made with five head welding machine.
Samples representing each weld head were taken.
4
Table No. 3
- Shear Load Test Summary (1978)
Unistrut No. Of Sj] EAR _ LOADS _(1bsy Part No.
Specimen 41,200 4 2,400
<3,200
>3,200 P-1001 Callaway 91 0
5 5
81 Wolf Creek 125 1
1 2
121 (A) TOTAL 216 1
6 7
202 P-5501 Callaway 12 0
1 5
6 Wolf Creek 56 2
1 2
51 (B) TOTAL 68 2
2 7
57 P-5001 Callaway 23 0
0 1
22 Wolf Creek 73 0
2 0
71 (C) TOTAL 96 0
2 1
93 380 3*
10 15 352 TOTAL (A+B4C)
(1) 2 were from Coil No. 7J-4661, Part No. P-5501.' Total of 6 samples from this coil were tested. 3 were above 4,000 lbs., I was 1,400 lbs., and 2 failed at sawcut.
(2) I was from Coil No. 7X-4444 (P-1001).
A total of 15 sampics were tested, twelve were above 3,200 lbs, two were above 2,400 lbs, and only one was below 1,200 lbs.
There were 15 samples from Coil No. 7K-4444 (same coil as 7X-4444, but different operator), 14 were above 3,200 lbs., and one was at 2,350 lbs.
When adjacent welds were tested, average load exceeded 3,200 lbs.
P Page 11
Table No. 4
- Retest of Specimen, Below 3,200 lbs, Shear Load.
(1978)
Unistrut No. Of AVERACE SHEAR LOAD (lbs.)
Part No.
Specimen 41,200 42,400
<3,200
>3,200 P-1001 Callaway 10 0
5 4
1 Wolf Creek 4
1 1
1 1
(A) TOTAL 14 1
6 5
2 P-5501 Callaway 6
0 0
6 0
Wolf Creek 5
2 1
2 0
(B) TOTAL 11 2
1 8
0 P-5001 Callaway 1
0 0
1 0
Wolf Creek 2
0 2
0 0
(C) TOTAL 3
0 2
1 0
TOTAL (A+B+C) 28 3
9 14 2
Note:
1.
Average shear load is the average of two adjacent welds and the original specimen.
2.
Three specimens with a shear load below 1,200 lbs., are the same three specicens described in Table No. 3.
9 Page 12
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