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EJAM7-3NT72 A New Mechanical Condition-based Maintenance Technology Using Instrumented Indentation Technique
EJAM7-3NT73 Survey robots for Fukushima Daiichi Nuclear Power Plant

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(EJAM): ejam@jsm.or.jp
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HP: http://www.jsm.or.jp
(in English)

 
Vol.1 No.1 ← GA 5 - AP 6 - 7 - NT 7 - 7(1) - 7(2) - 8 - 9 → Vol.1No.3
Vol.1, No.2, NT9 EJAM (1-2-NT9) - HSW (Heat Sink Welding): Preventive Maintenance Technique for Primary Loop Recirculation Piping

HSW (Heat Sink Welding)
Preventive Maintenance Technique for Primary Loop Recirculation Piping
 
TOSHIBA CORPORATION
 

KEYWORDS：
SCC, PLR piping, austenitic stainless steel, sensitized zone, stress improvement, HSW
 
1. Technical summary
 
Classification
(I: Inspection, II: Repair, III: Replacement, IV: Preventive Maintenance, V: Others)
 

This technique can reduce tensile residual stress near the inner surface of pipe weld which is the stress factor of SCC, utilizing the thermal stress distribution.

Initially the barrier to water is composed by in-air welding up to 2 to 3 layers and after that welding is carried out as cooling inner surface with watering or spraying (Fig.1). Through this process, thermal stress is induced due to temperature difference through the thickness.
 
2. Scope

(1) Components：Stainless steel piping such as BWR PLR piping
(2) Object Location：SCC Sensitized zone of the base metal near the weld
(3) Material：Austenitic stainless steel
(4) Applied Condition
　　a) This technique can be applied to the pipe joints welded in workshops, and also applied to the field welding.
　　b) This technique is applied under the air condition with cooling water or spraying water inside the pipe.
EJAM1-2-NT9-Fig.1(a)(small)HSW_by_watering EJAM1-2-NT9-Fig.1(b)(small)HSW_by_water_spraying
(a) HSW by watering[1] (b) HSW by water spraying[2]

Fig.1 Concept of HSW
 
3. Features

Prevent initiation of SCC by suppressing tensile residual stress of base metal near the weld inside the pipe. Sample of stress improvement by this technique is shown in Fig.2.
EJAM1-2-NT9-Fig.2_Residual_stress_distribution_on_the_pipe_inside_surface

Fig.2 Residual stress distribution on the pipe inside surface

 
4. Examples of Application
This technique was applied to BWR PLR piping.
 
5. Reference
(1) Teruaki Sato, Kazuyoshi Yonehara, Satoshi Hongo, Shoji Hayashi and Hideyo Saito,” Introduction of Replacement and Maintenance Technology against SCC in Recirculation Piping (PLR Piping) of Nuclear Reactor”,Maintenology,Vol.3,No.3(2004)
(in Japanese).
(2) The Japan Welding Engineering Society, < http://www-it.jwes.or.jp/qa/details.jsp?pg_no=0090050040>
 
6. Contact
Japan Society of Maintenology (ejam@jsm.or.jp)