ML20127J741
| ML20127J741 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/10/1966 |
| From: | Bolotsky M, Holt A US ATOMIC ENERGY COMMISSION (AEC) |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9211190410 | |
| Download: ML20127J741 (13) | |
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() t y DIemorandwn , j i TO ! Files , u.a. (C 10 . b A. B.11olt, Chief bhW b d, ! FRW M. Bolotsky * '. , . bob'y ! Technical Assistance Branch, SS i W8)MI VISIT ON SEPTEMBER 30, 1966, TO ATLANTIC REFINERY, PHILADELPHIA, PENNSYLVANIA, TO OBSERVE FIELD ERECTION OF A PRESSURE VESSEL l DIMENSIONALLY SIMILAR TO THE PROPOSED MONTICELLO REACTOR VESSEL so- 243 INTRODUCTION- l On September.30, 1966 AEC Regulatory Body personnel visited the Atlantic . Refinery at Philadelphia, Pennsylvania, to inspect a hydrocracker ' pressure vessel that is being field erected by the Chicago Bridge & Iron Company, The latter company has beensolected by the General Electric Companyj to field erect the reactor vessel of the Monticello, Minnesotta, Nuclear ,
' Generating Plant of the Northern States Power Company. The Atlantic-Refinery pressure vessel was selected for inspection because it is similar dimensionally to the Monticello proposed reactor vessel, as shown by the l following tabulation of vessel parameters that was obtained from P. C.
Arnold, Vice President and Director of Welding, CB&I. Atlantic Refinery Monticello vessel Vessel Parameter Vessel Code ASME, III, Class A ASME, III, Class A Plate Material A387-D (2.5 Cr,1Mo) A302B. nickel modified Overlay Material Ty'pe 347 stainless steel Type 308 stainless steel 1 17' 1" Inside Diameter 13' /2" Inside licight 79' 0" '63' 1 /2" Thickness 11/ 16" 13 Top 11ead 3 2 /16" 1 Shell 6 7
/8" 5 /4" 11 5 1 - 6 /4" Bottom Head 3 /16" 74 Weight 575 tons 600 tons Operating Temperature 800 - 850*F, approx. 550*F-Operating Pressure- 2000 psi, approx.= 1000 psi Main Components Bottom llend Bottom Head (Hemispherical) (Hemispherical) 10 Shell Rings 4 Shell Rings (Assembled at CB&I Shop) (Assembled at site)-
Top' Head' IE888bangeE" Hem a herical) Top llead (llemispherical) i
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9211190410 661010 POR ADOCK 05000263- .w
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(' ) Files The following persons visited the Atlantic Refinery vessel: R. S. Boyd - DRL C. W. Rein:uuth - C0 B. Crimes - DRL H. D. Thornburg - Senior Reactor J. J. Shea - DRL Inspector, CO, Chicago Office A. B. Ilolt - SS R. A. Lofy - Parameter, Inc., M. Bolotsky - SS consultant to CO and DRL The following CD&I personnel were met at the site of the partially crected vessel: P. C. Arnold - Vice President and Director of Welding J. Cristofori - Welding Manager, Eastern Area D. Moody - Job Superintendent A. Potter - 11 cad Welding Supervisor at the site - The vessel was inspected during the noon lunch break of the vessel erection crew. Discussions were held with CBLI personnel before, during, and following vessel inspection.
SUMMARY
OF OBSFRVATIONS AND DISCUSSIONS WITH CB&I contracturni Set-up at Atinntic Refinery Vesnel The main contractor for the plant modification at the Atlantic Refinerv if the Fluor Corporation, which subcontracted the fabrication and erection of the hydro-cracking vessel to CB61. The vessel vill be owned by CD&I until it is turned over tto the Atlantic Refinery af ter successful com-pletion of the acceptance hydrostatic test required by the ASME Code. Pref abriention of Vennel Components After prefabrication at CB&I's principal fabricating shop, located at Birmingham, Alabama, the vessel components are railroaded and trucked to the Atlantic Refinery site. The shell rings come as completed cylin-drical sections containing nozzles and longitudinal volds that were put in at the shop, whereas each of the Monticello vessel shell rings will k be delivered as two halves which will have to be assembled at the site prior to crection. Fitti a e and stress relieving the welds can he welding the'longitudina scamch,twohalvesofashellringtogether, f g5e donc much more readily a e' shop than at the site in a temporary field t,\ shop. Consequently, it will be much more difficult to achieve proper [([g/ shape and dimensions for the Monticello shell rings. U 2
_ _ - . _. n i (* l 4 Files OCT 101966 i Also, at the Atlantic Refinery the botton head and skirt were received as one completed component (See Fig.1 of Appendix 1 of this memoran- , dum), whereas Appendix G of the" Facility Description and Safety Analysis ! l Report" for the Monticello Plant indicates the possibility that both ! the top head and bottom head may have to be shipped to the site in I
; sections. This will require even more difficult fit-up and welding than will be the case for assembling the shell rings. Fig. 2 of Appendix 1 illustrates, schematically, the field shop welding that will be necessasy j for the bottom head in this event.
f welder Ounlification I By agreement with the boilermakers union, presnure vessels must be built a with only local people. However, union headquarters does allow CE&I to bring in CB&I welders for critical locations to the extent that they constitute only an agreed upon percent of the total boilermakers on the job. An alleviating factor is that most of the boilermakers who work on pressure vessel erection do jobs other than welding. At the Atlantic Refinery site there was a good supply of local welders who had worked previously for CD&I. Therefore, there was no problem
- in regard to having only experienced welders do the vessel welding.
j Moreover, in addition to first having to pass the ASME Code required welder qualification test, all of the velders were trained by CB&I at the site. This training consisted of practicing on a typical joint of the same material, material thickness, geometry, etc., as in the vessel. Only when their welding was considered satisfactory by the CB&I weld-ing supervision were the welders allowed to begin work on the vessel. ! The same system of welder qualification will be used at the Monticello site. According to Mr. Arnold, there are sufficient local welders there who have worked for CB&I that, despite the union restriction, about 90% of the Monticello vessel welders will be welders -who have previously welded CB&I vessels. Fit-up of Vessel Sectionn The as-received vessel heads and shell rings are inspected for out-of-roundness and other possible dimensional defects before being accepted as fit for erection. Before welding can be done each head and each ring must be satisfactory in regard to sidewise matching of the shell courses (see Fig. 3 of Appendix 1) and in regard'to plumb. l 1
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j * . (, . .' OCT 10 26 i Tiles 4 Article 5 (" Fabrication") of Section III of the ASME Code reflects both the difficulties encountered in velding plates to true cylindrical shape and the necessity that matching ends of shell rings and formed heads be not offset toefar prior to welding. i The first part of Item N-517 (" Tolerance for Formed Heads") of Article
- 5 reads
"The 6k irt or cylindrical end of a fortned head shall match 1 the cylindrical edge of the adjoining part within the tolerance specified in N-525 and shall be truly circular to the extent that the difference in inches between the maximum j and minimum diameters does not exc.eed the smaller of E + 50 200 i f00,whereDisthenominalinsidodiameterininches.
The first part of Item N-525 (" Alignment Tolerance") of Articic 5 statest 4
"N-525.1 Alignment of sections at edges to be welded shall be such that the' offset of the thinner section is not greater than the value shown in Table N-524, where t is the nominal section
- thickness of the thinner section at the joint
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Tabic N-525 MAXIMUM ALLOWABLE OFFSET IN VELDED JOINTS Direction of Joints in ' Cylindrical Shells i Section Thiekness Lonnitudinal Circumferentia! Over 2 inches 1/8 inch 1/4 inch" ^ ' 0 Item N-516 (" Tolerance for Shella") of Article 5 also requirea that i all cross sections of cylindrical shells meet the D + 50 and D 200 100
, requirement. It is noteworthy that the AS"E Code will aHow the Monticello vessel rings to have the largest dinteeter exceed the smallest diameter
. by as much as 205 + 50 inches. Although such a degree of out-200
= .27 of-roundness would hardly permit compliance with Table N-525, it is apparent that the fabrication tolerances of the ASME Code will allow out-of-alignment and flat spots to be present in the Monticello vessel and that their.cxtent will depend only upon the quality of the CB&I work'at the site.
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( v l I OCT 101966 d Files ' 1?cid Joint Prennration An essential part of CB&I's procedure for obtaining sound girth velds of thich walled pressure vessels is the use of a ring,1/2 inch by 1/2 inch in cross section, and a corresponding certain veld joint contour, both shown by Fig. 4 of Appendix 1. Each ring is made from the same material as the vessel shc11 material. Each cylindrical scetion is received from Birmingham with a ring machined flush with J and tack welded to the top of theweld joint, at the upper part of the section. The_next vertical cylindrical course is placed on the ring with no play between the surfaces. In case the two sections to be volded are out of alignment. the upper veld joint is machined so as to match the ring, thus resulting in 4 the vessel shell contour shown by Fig. 5 of Appendix 1. By this wcld preparation a sound root pass can be obtained even if the outer and inner surfaces of the matching components are not exactly co-axial or cxhibit flat spots. The deficiencica in geometry are f aired out by
- weld metal, and, after velding, the surfaces are ground to the finish needed for~ ultrasonic examination and radiography.
Ucidinn Prehentinn It has been found by CB&I that successful welding of ferritic steci pressure vessels requires maintaining a temperature of 300-400*F at the wcld joint continuously until the weld is post-weld stress re-lieved. This is achieved by strapping cicctrically heated circular pada to the outside of the vessel, both above and beneath the joint to be volded. In order to allow access to the hot weld joint by the velders working at the outside of the vessel, the preheating bands are in-sulated at the outer surfaces. The preheat made the inside of the vessel very hot in regard to comfort of the welders working at the inside. Consequently, CB&I had an air conditioning unit hooked up to cool theevessel interior at the veld in progress. Even so, inside temperature was so high that tha eye goggles of the welders readily became covered with perspiration, 'thus mpairing their vision during volding. _Ucidinn Procedure Welding is begun _by first putting down four circular layers of veld metal at the inside face of the veld joint ring (see Fig. 4) using 5/32 inch diameter electrodes. During this time, and thereafter, a CD&I welding supervisor visually examines each vold pass as it is completed individually. Af ter completion of the fourth. pass, the veld is ex-amined by Magnaflux. Then the weld ring is removed from the outside-by are gouging or chipping, and the veld root is Magnafluxed. Next, four veld beads are applied at the veld root, and tdagnaflux examination is then given these wcld passes. Thercafter, welding is donc simultan-
( _) l OCT 101966 Files l l l cously at both sides of the wcld joint. After the first five or l six wcld passes have been completed, larger size cicctrodes are used to complete the veld (i.e., 3/16 inch diameter). Control of Veldinn Rod Mofnture k'clding rods are baked in ovens at the site for three hours at 800*F. l This reduces the moisture content of the coating of the as-received ]; rods from 0.02% to 0.01%. They are then transferred to holding ' ovens which keep them at 250*F until they are used. The holding ovens are at the hot velding area, so there is no opportunity for the rods to absorb moisture before use. Baking the cicetrodes prevents the possibility of absorption of hydrogen by the wcld and therefore . presents wcld cracking due to hydrogen. l Hot Ultresonic Examinntion of Ucids 11pon completion, each girth veld is shear uavc ultrasonichily in- , spected while being maintained at 300-400*F by the preheaters. The ultrasonic examination is done with the veld hot so that any defects found can be repaired at this time, prior to post-wold stress relief. CB&1 clains that their hot ultrasonic test sensitivity is better than what the ASME Code requires when it specifics ultrasonic testing, which is donc at ambient temperature. CBLI considers the details of their technique to be Company Confidential and therefore did not discuss them. It is pointed out that the ASME Code does not require ultrasonic examination of the longitudinal and cire'umferential velds in the shcIl of a pressure vessel. First pont-k' eld Stress Relief When the hot ultrasonic examination has shown that a weld is sound, a temporary furnace is built aroung the veld. By means of oil burn-ers placed at the inside.of the vessel plus proper baffling and in-sulation, the veld region is heated gradually to 1200*F and held at tempera-ture for one hour. The preheaters continue to operate follouing the ultrasonic inspection until the oil burners have taken over the heating of the veld region. Following the one hour stress relief, the wcld is allowed to cool to ambient temperature. Gamma Rt.dionraphy of Ucids Now that the veld has been stress relieved, it is safe to allow it to cool to ambient temperature in order to conduct 100% radiographic ex-amination of the weld, as required by the ASME Code. CBLI has f.aund that pressure vessel steci velds are prone to crack if allowed to reach ambient temperature without first having been stress relieved. .It is necessary to conduct radiography at ambient temperature because the radiographic film cannot withstand exposure to preheat temperature. [:
00T 10 26 Files f f : T At the site, CB&I conducts radiography by means of a cobalt 60 sourec. This is suspended inside the vessel at the center location relevant to i the wold, film packs are placed against the wcld region at_the vessel j outside, and,onc exposure of almost 24 hours then radiographs the en-tire girth veld. Mr. Arnold maintains that, despite the long exposure, I the 1% sensitivity required by the ASME Code for 6-8 inch thick volds is achieved (see Item N-624, " Technique for Radiographic Examination l of Wclded Joints," of Section III of the Codo). I In the CD&I Birmingham Shop a wcld of this thickness would be radio- ! i graphed by means of the CB&I 25,000,000 voit botatron, with resulting sensitivity of 1/2%, according to Mr. Arnold, However, Mr. Arnold feels that this difference in sensitivity is not significant._ Mr. Arnold stated that even if a portabic betatron existed, it would not be feasibic to uso it in the field because of the shiciding probicm. i Actually, CBLI is not concerned about cobalt 60 radiographic sensi-tivity because of their faith in the reliability and sensitivity of their hot ultrasonic testing technique. Weld Renion Stainlenn Steci Overlay _ Next, the inner and outer faces of the weld region are clad by stain-1 css steel wcld overlay. Details of this step were not discussed with CBLI. Ultrasonic Exanination of Claddine This inspection is done to verify that bonding between base metal and cladding is sound. Assuming that the wcld region was-preheated _ prior to cladding, again the ultrasonic inspection would be done hot. Final Post-Ueld Stress Relief Upon assurance that the stainicss steel overlay is proper, the veld region is now given a second post-wold stress relief treatment at 1200*r by the technique described previously. This time the veld is held at temper-ature for one hour per inch of thickness, as required by the ASME Code (sco Tabic N-532 of Section III of the Code). For the Atlantic Refinery vessel this means seven hours at temperature. When asked why the first stress relief is done for only one hour, Mr. Arnold replied that the shell material could accept only a certain number of hours at stress relieving temperature without degredation of its mechanical properties. If defects requiring wcld repair were found after the first stress relief treatment, additional stress relief time would be necessary prior to the final stress relief operation. This has to be allowed for.
( riles OCT 101956 Final Nondestructive Insocetion of Ucids Mr. Arnold mentioned that, in compliance with the request by the Atlantic Refincry, the girth walds, now clad, would be radiographed a second time. Also, a third ultrasonic inspection would be conducted, this time at ambient temperature on the clad wcld regions. The conversation on these topics was held while inspecting the vessel and was not amplified later because the visit in the afternoon was curtailed unexpectedly by the
, necessity that Mr. Arnold meet with Atlantic Refinery personnel. Whether or not CB&I intends to perform a second radiographic examination and a third ultrasonic inspection of the Monticello vessel velds was not dis-cussed.
Schedule for Joinint Two Shell Sectionn The following is an approximate schedule of operations involved in joining two shell sections. It was obtained from conversation with Mr. Arnold and Mr. Cristofori and may not be exact or complete because of . lack of time to check each item. Days Operation Required
- 1. Inspection for out-of-roundness and fit-up to match the base 1
- 2. Weld preheating, root welding, and Magnaflux of wcld root passes 1
- 3. Completion of welding 7
- 4. Hot ultrasonic inspection of wcld region 1/2 day S. Post veld-stress relief of weld region, for 1 hour 2
- 6. Cooldown from post-weld stress relief 1
- 7. Gamma radiography of veld region 1 8 Weld preheating and stainicss steci overlay at veld region 2
- 9. Hot ultrasonic inspection of cladding at veld region for bonding 1/2 day
- 10. Final post-weld stress relief of veld region, for 7 hours 2
( .i OCT 101966 Files 11. Cooldown from final post-weld stress relief 2
- 12. Final gamma radiography of wcld region 1
- 13. Final ultrasonic inspection of wcld region 1/2 dav Total time for above operations 21-1/2 days CB&T Ouality Centrol The direct control is exercised by a welding supervisor and an assistant on cach shift. The duty of the welding supervisor is to certify each veld pass. The assistant to the velding supervisor takes carc of the usual supervisory chores arising from the vessel crection. The CB&1 welding inspectors report to the licad Welding Supervisor at the site.
The welders are paid per hour and not per foot of weldment. A bonus is paid for clean " radiography". Thus, the welders arc encouraged to take their timo and do their best work. CONCLUSIONS The fit-up procedurcs, welding methods, and quality control procedures in offect by the Chicago Bridge & Iron Company at the Atlantic Refinery site for assembling the 13 foot, 6 inch diameter hydro-cracker pressure vessel are so ucil developed that one has no hesitation in' accepting the , CD&I claim about the Code compliance of the vessel. l Out of roundness and small irregularities introduced during fit-up are more difficult to cope with for CD&I because of the lack of facilitics in the ficld (i.e. , rolling equipment, heat treating furnaces, etc.) .This means that when two cylinders are welded together misalignments can not be corrected. At the Atlantic Refinery site because the pressure vessel is wclded up from prefabricated rings, the fit-up is easy and the weld-ing groovo nearly as perfcet as one may.vish for. When one is compelled-to start with two half rings at the crection site, as will be the case for the Monticello vessel, whether or not the results will be proper cannot be stated from just the visit tc the Atlantic Refinery vessel. This point needs much further consideration.
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b Of110IN$ Files The process of radiography used by the CB61, i.e., the use of cobalt 60 cource in the center of the vessel plus an exposure tino of many hours, does not give as good sensitivity as can be obtained when 6-8 inch thich ucids are radiographed in the shop by ccans of a betatron. A point to be resolved in whether or not hot ultrasonic inspection plus cabalt 60 radiography are sufficient.
Attachment:
Appendix 1. ,. '$ cci P. Morris, Dir., DRL/w/att. E. Case, Dep. Dir., DRL/w/att._ J. J. DiNunno, Asst. Dir., SS/w/att. R. Boyd, DRL/w/att. J. Shea, DRL/w/att. C. Reinmuth, 00/w/att.
- H. Thornburg, CO, Field Office, Chicago, w/att.
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