ML20198E931

SER Recommending Applicant Actions Re Magnetic Particle Linear Indications on Containment Weld Pads

ML20198E931
Person / Time
Site:	Columbia
Issue date:	01/23/1984
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20197G231	List: ML20197G228 ML20198E931
References
CON-WNP-0789, CON-WNP-789 NUDOCS 8605280358
Download: ML20198E931 (5)

Text

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ATTACHMENT SAFETY EVALUATION REPORT WASHINGTON PUBLIC POWER SUPPLY SYSTEM NUCLEAR PROJECT N0. 2 DOCKET NO. 50-397 MAGNETIC PARTICLE LINEAR INDICATIONS ON CONTAINMENT WELD PADS MATERIALS APPLICATION SECTION MATERIALS ENGINEERING BRANCH BACKGROUND Purpose of Weld Pads There are 19 containaent shell weld pads at the 512' and 524' elevations which are steel plates, two inches in thickness, round or rectangular in shape, and approximately five feet in diameter or length of side.

Beam seats are welded to the pads, and the seats support the radial

+ beams between the Mark II boiling water reactor containment shell and the drywell .

Each pad attaches to the containment shell with a 3/8" fillet weld for t.he entire periphery of the pad. This is the minimum allowed fillet weld size for joints with material two inches in thickness as required l

l by the American Society for Mechanical Engineers Boiler and Pressure Vessel Code,1 Section III, Subsection NE, " Class MC Components." The peripheral welds are adequate by themselves to take all loads. There are redundant plug (circular fillet) welds within the pads that also attach the pads to the containment shell which are also capa' ole by themselves of supporting all the loads. The plug welds are a little over two inches in diameter and range in size from 1/2 to 5/8 inch.

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History of Events The Quality Verification Program required reinspection of a sample of attachment welding to the containment vessel under Contract 213. Rein-spection by magnetic particle testing (MT) revealed linear indications beside the thick weld pads' peripheral fillet welds to the steel containment shell. The reinspections were expanded to all 19 two inch thick pad attachments and all had linear indications. The indications have an average length of 3.3 inches on the pad side and grinding showed average depths of approximately 1/4 inch. Metallurgical investigations determined the indications in the weld pads and shell to be hydrogen underbead cracks.

In the weld pads, some of the underbead cracks ended as lamellar tears.

For the linear indications in the containment shell plating, metallurgical examination and ultrasonic testing (UT) showed no evidence of lamellar tearing, and the shell MT indications' lengths averaged about half of those in the weld pads. All peripheral fillet welds around the weld pads at the 512' and 524' elevations had their magnetic particle indications removed by grinding. These fillet welds were weld repaired and weld built-up to 1/7 inch, exceeding their original size of 3/8 inch, I

and the final welds met MT inspection criteria.

The 19 weld pads also have 405 plug or circular fillet welds which also attach the wild pad to the containment shell. A statistically significant (55) of these welds were inspected by liquid penetrant testing and 13 had linear indications. The indications were removed by grinding to sound metal demonstrated by liquid penetrant inspection, and the excava-l tions were allowed to remain as is.

These welds were not restored to their design configuration because:

o design did not require them as they were redundant to the peripheral fillet welds, o repair of these welds in these small holes would be very difficult.

o fracture mechanics analysis determined that the flaws were innocuous.

The inspections were further expanded to include ten other field welded pads of smaller size in the drywell and a sampling of all other attachment welds to the containment shell.

A few magnetic particle linear indications and one UT indication where (MT was not practical) were found. The total length of the indications is less than 1% of the lengths of welds reinspected. This ratio is normal for reinspections of structural steel weldments. The indications were short in length, and, where depths were determined, very shallow (maximum of 1/8 inch). Most MT linear indications were removed by grinding and weld repaired. Fracture mechanics analyses were performed based upon the largest size of the flaws found which far exceeded the size of linear indications not repaired and the analysis demonstrated that the flaws remaining would not propagate.

DISCUSSION / EVALUATION The extent and severity of the linear indications found on the original 19 thick weld pad attachments were not repeated in the expanded surface and UT examinations. This indicates that the original causative factors of cracking in the two inch thick pad weldments were unique, a local problem, and not generic to other. welded steel structures.

The expanded reinspection sample size appears adequate. The small per-centage of li.near indications length found vs. total length inspected is normal for reinspections of steel weldments which had previously been inspected. The AC yoke magnetic particle inspection method is an acceptable surface inspection technique. There are other magnetic particle inspection techniques which are more effective for detecting defects which do not break the surface, such as underbead cracking and lamellar tearing, the crack causing mechanisms in this case. However, the configuration of the assembly, and the sequence of fabrication and loading caused the underbead cracks to break to the surface or caused lamellar tears to initiate at the surface. Accordingly, the AC yoke method is viewed by the staff as acceptable for this application. At the present time, we do not have a demonstration that would convincingly justify our establishing particular surface examination techniques for structural steel constructions. The fracture prevention approach by the applicant is a standard app' roach, often used and accepted by the staff for many other applications.

CONCLUSION Based upon the data presented, we recommend acceptance of the applicant's actions.

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