ML20116F455

Intervenor Exhibit I-159,consisting of Pp 80-90 of Item 12, Investigation/Resolution of Concerns, Re Concern 1, Interpass Temp

ML20116F455
Person / Time
Site:	Catawba
Issue date:	10/11/1984
From:	Kruse B, Llewellyn D AFFILIATION NOT ASSIGNED
To:
References
OL-I-159, NUDOCS 8505010101
Download: ML20116F455 (12)

Text

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l. - . 69 Item 12 INVESTIGATION / RESOLUTION OF CONCERNS Page 1 of 6 ASSIGNED TO: D. H. Llewellyn CONCERN NUMBER: 1 INTERPASS TEMPERATURE Statement of Concern Ten welders had concerns regarding potential violations of maximum interpass temperature requirements for welding on safety related systems.

Plant procedures require.that between welding passes the temperature be allowed to decrease below the maximum interpass temperature (350*F for stainless steel and 500*F for carbon steel) prior to starting the next pass. The concerns of the ten welders are as follows:

1. While four of the ten welders knew of no specific instances of violations, three (Individuals 6, 12 and 81) felt there may have been unintentional violations by other welders (not themselves), and one felt that he could possibly have at one time also unintentionally violated interpass temperature requirements (Individual 38). Two of the four individuals (81 and

38) felt that these unintentional violations might be due to production pressure by foremen. However, all of these individuals felt that the violations, if they occurred, were minor and had no impact on the quality of the welds.

2. Six welders stated that they knew of specific instances of violations of interpass temperature requirements.

(a) One welder (Individual 36) alleged that he was directed by Individual 142 to make the fourth pass on a stainless steel weld after the metal had cooled for about 10 minutes. He stated that at this' point he could hold his hand on the weld for only 1 second. The welder speculated the temperature was still above 350"F. The welder stated that the weld was later cut out.

(b) One welder (Individual 106) alleged that he was directed by his foreman (Individual 78) to climb back up a scaffold and make the second pass on a stainless steel weld after the weld had cooled for over 3 minutes. During this time the welder had climbed down a scaffold and began talking to another worker, while his foreman had climbed up the scaffold and with his hand checked the weld temperature. Again, the welder was speculating that the temperature was still above 350*F.

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(c) Two welders (Individuals 70 and 196) stated that they and other welders were directed by their foreman (Individual 142) to make between 12 and 24 stainless steel socket welds in the Unit 1 pipe chase as fast as possible without regard to interpass temperature requirements. Significantly, welder 196 described the situation and production pressure as follows:

"On interpass temperature, [ foreman 142] told us when we were working 'on stainless steel to keep using the temp stick and the minute the pipe was cooled below 350 degrees to start back on the weld. Someone asked the question if this procedure would affect the fitting and [the foreman] said that in his opinion, it would not."

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Item 12 INVESTIGATION / RESOLUTION OF CONCERNS Page 2 of 6  !

CONCERN NUMBER: 1 I

Statement of Concern (continued) - -- _'

(d) One welder (Individual 192) " heard" of welding conducted by another (Individual 67) after an inspector had determined the weld joint was still too hot to weld. Significantly, when interviewed, Individual 67 knew nothing of the incident. (Foreman override was not alleged.)

(e) One welder (Individual 14) knew of a weld in the " pump structure" where interpass temperature may have been violated. However, he stated that the weld was later cut out. (Foreman override was not an issue and he felt the violation was unintentional.)

l TYPE OF CONCERN: _X_ FOUNDED

- UNFOUNDED Q-1A REQUIRED YES X NO Q-1A NUMBER Investigation The investigation consisted of interviews with welders and supervisors, review of appropriate codes and procedures, testing of weld samples, and an evaluation of the chemistry of Catawba's process fluids with regard to stress corrosion cracking.

' Interviews 1.

All welders interviewed were specifically asked if they had any knowl. edge of interpass temperature violations. Of the 134 welders interviewed, only the ten noted above raised concerns regarding violation of interpass temperature requirements. Further, of these ten welders only six had heard of specific incidents and only four stated that they had direct knowledge of interpass temperature violations. Further, those who alleged direct knowledge did not use a temp stick or other positive method of determining whether interpass temperature requirements had been violated; rather, they speculated that the

maximum interpass temperature specified by procedure may have been exceeded.

Indeed, two of the four appear to have had a very conservative impression of what the maximum interpass temperature requirements were. Significantly, many welders stated that with stainless steel you had to let it cool below 350*F or it was difficult to weld. It should be noted that if this difficulty resulted in unacceptable indications they would be detected in the subsequent QC inspection).

2. Testing of Coolina Times Duke conducted tests to investigate the two welders' allegations (noted above) that (1) a delay of about 10 minutes between the third and fath pass of a 2 inch stainless steel heavy wall socket weld and (2) a delay of over 3 minutes between the first and second pass of a stainless steel weld on a 6 inch schedule 40 pipe were insufficient times for the welds to cool below the 350'F interpass temperature required for such welds. Testing was performed on 4

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Item 12 INVESTIGATION / RESOLUTION OF CONCERNS Page 3 of 6 CONCERN NUMBER: 1 Investigation (continued) numerous samples of various sizes (including those noted above) to determine the length of' time it took for the temperature of the weld joint to drop below 350*F.

The test results reflected that for the heavy wall 2 inch socket weld, the maximum cooling time required for the temperature to drop below 350*F for any pass was 7 1/2 minutes; for the third to fourth pass the time was 4 1/2 minutes

- much less time than the 10 minutes which the welder stated had elapsed. In short, in this instance maximum interpass temperature requirements were not exceeded.

The test results for the 6 inch schedule 40 w(ld reflected that the required cooling time was 21/2 minutes between passes 1 and 2, 31/2 minutes between passes 2 and 3, and 6 minutes between pass 3 and the final pass. The welder had stated that 2-3 minutes of cooling time had elapsed when the welder was directed by his supervisor to continue welding. To continue welding, he had to. wait for his foreman to climb down from a 5 foot scaffold, climb the scaffold, and prepare himself to weld before he actually started. Thus, before he started welding at least 3 minutes time had elapsed. This is greater than the 21/2 minutes cooling time needed for the interpass temperature to drop below 350*F between passes 1 and 2, as reflected by the tests noted above.

Accordingly, in this instance the weld was also well below the 350*F maximum interpass temperature.

- The fact that several of the welders making allegations felt that they needed to be able to place their hands on the weld for one to two seconds without pain before they considered it safe to weld, reflects the conservative misconception of some welders at Catawba. Clearly, a welder would not be able to hold his hand on a weld joint that was at 350*F for a second or more without severe skin blistering. This misconception in all likelihood accounted for some, if not all of the allegations. Significantly, this misconception reflects the conservative approach of the Catawba welding program.

3. Code Requirements The only ASME or AWS code requirements regarding maximum interpass temperature relates to welding on material subject to charpy impact testing.

The subject of the few specific concerns raised in this area were exclusively l related to stainless steel. Stainless steel does not require impact testing, j and thus there is no code requirement regarding interpass temperature. No one alleged any specific instances of maximum interpass temperature violations on any other type of material (much less on material subject to charpy impact i testing). In short, the few allegations regarding exceeding maximum interpass

! temperatures do not in themselves represent violations of any code requirements. However, Duke has committed to comply with NUREG-1.44 which recommends a maximum interpass temperature of 350*F for stainless steel welding.

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Item 12 INVESTIGATION / RESOLUTION OF CONCERNS

.! Page 4 of 6 CONCERN NUMBER: 1 Investigation (continued)

4. Testino of Stainless Steel d

Duke Nuclear Guide 1.44, paragraph 6.0, requires that a maximum interpass temperature of 350*F be observed for welding on stainless steel to minimize the weld heat affected zone sensitization. Weld heat affected zone sensitization is manifested as a precipitation of chromium carbides at the grain boundaries I

of the stainless steel material. If this condition occurs and is severe, the stainless steel will be more sensitive to corrosive attack in certain aggressive environments. (As will be discussed later, such aggressive environments are not present at Catawba.)

To determine the effect on stainless steel of exceeding the interpass temperature requirement, Duke conducted tests consisting of welding stainless steel samples using interpass temperatures ranging from 250*F to over 750*F (well above the 350*F specified by procedure). Significantly, one of the test i samples was welded by the welder (noted above), who alleged that 12-24 such welds had been welded in violation of interpass temperature requirements. The

- welder attempted to recreate the worst case condition he had experienced.

A metallurgical evalaution was performed on the test sample to determine whether the degree of sensitization was significantly affected by the range of interpass temperatures used in the tests. The results reflected that there was no appreciable difference in the severity of sensitization for these ranges of interpass temperatures, i.e., 250*F - 750*F. These results were confirmed by s subsequent field testing.

! In order to further substantiate these results, J. A. Jones' Applied j Research Laboratory (an independent organization) employed the electrochemical potentiokinetic reactivation technique on the test coupons. Their conclusions

! were:

a. Test results were consistent with the aforementioned test results,

b. That for these test coupons, interpass temperature did not appear to influence the d7 gree of sensitization.

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c. The heat affected zone did not appear to be significantly different from unaffected base material conditions.

5. Evaluation of Catawba's process Fluids Even assvning that severe sensitization of the stainless steel occurred, the corrosive environment necessary to lead to intergranular stress corrosion

cracking ("IGSCC") (the potential adverse consequences of such sensitization) is not present at Catawba.

i Stainless steel is susceptible to stress corrosion cracking when exposed ,

! to the correct aggressive environment. In' a nuclear power plant the relevant possibly aggressive environment is the reactor coolant or process fluid with the presence of an active anion corrodant. Examples of such active anions are l

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, INVESTIGATION / RESOLUTION OF CONCERNS Page 5 of 6 CONCERN NUMBER: 1 Investication(continued) l

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oxygen, chlorides, fluorides, sulfides and sulfate ions. Simply the presence

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- of these anions is not enough to cause IGSCC; they must be present in significant concentrations.

4 The specifications for Duke's McGuire Nuclear Station coolant chemistry

, are attached as Enclosure 1 to the discussion. The Catawba specifications are i

! currently -in the process of final drafting, so they are not available for *

! attachment to this report. However, they will be the same as McGuire, or in some cases more conservative. Significantly, in every case, concentrations of potential corrodants in the Catawba aqueous environment which could lead to IGSCC are well below the critical concentrations identified by experience and research.

In sum, process fluid chemistry and impurity controls at Catawba create an aqueous environment which will not result in IGSCC. However, even assuming that IGSCC occurs, a major LOCA would not be expected. Any form of stress corrosion cracking in ductile austenitic stainless steel would lead to a leak before break event. With the leak detecting capabilities designed in the Catawba Systems, any leak would be detected before critical loss of coolant or process fluid occurred.

In summary, because the designed normal operating environment at Catawba i is not aggressive in terms of IGSCC, the possibility of sensitized welds does j not significantly increase the probability of stress corrosion cracking at Catawba.

Resolution-Conclusion

' Of the 134 welders interviewed, as set forth above, only 4 welders (3 incidents) alleged direct knowledge of interpass temperature violations on safety related systems. Further interviews and testing demonstrated that in l all likelihood these allegations were not actual violations. In short, there

is little evidence to confirm the allegations that interpass temperature was exceeded by craft. In any event, if interpass temperature requirements were

, violated, it is clear that the practice was not widespread, but consisted of l isolated instances. Moreover, if interpass temperature requirements were violated as specifically alleged, tests and research reflect that it would not have had an adverse impact on the integrity of the welds in question. It should be noted that in no case did a foreman direct a welder to violate

interpass temperature requirements. Rather, the few welders who raised this concern felt that the communications with the foreman left the impression that they were to rush at the expense of quality. The two foremen directly implicated by the allegations have either previously been removed from a supervisory position for reasons ' unrelated to this investigation (Individual

78) or will be so removed (Individual 142) for reasons stated in this report.

(See e Section VI of the main report.)

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Item 12 INVESTIGATION / RESOLUTION OF CONCERNS Page 6 of 6 CONCERN NUMBER: 1 Action No additional technical action is required. Personnel action will be taken in accordance with Section VI of the main report.

INVESTIGATION / RESOLUTION:

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FACE 29 OF 29 SECONDARY SYSTEM

WET LAYUP SPECIFICATIONS Duke Power Company McCulte Nuclear Station

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