Liner thickness measurement for zirconium lined zircaloy cladding tube using dual frequency eddy current method

This paper describes an automatic system for measuring the liner thickness of zirconium lined zircaloy cladding tubes (liner tubes) using a dual frequency eddy current method. The system consists of four components: probe coil, eddy current instrument, scanning mechanism, and mini-computer.Eddy current signals contain thickness information mixed with undesirable information resulting from variations in electrical conductivity of zirconium and zircaloy, and coil to conductor spacing. In order to calculate the liner thickness without a disturbance by such undesirable signals, an optimal equation is formed using signals obtained from a dual frequency eddy current method.It is revealed that the system is able to measure the liner thickness of liner tubes ranging from approximately 40 to 130 μm with an accuracy of a few micro-meters.     

Space charge effect for streamer initiation and propagation in water subjected to reciprocal traveling wave voltage pulse

This paper deals with initiation and propagation processes of streamer discharges in water subjected to high-speed repetitive voltage pulse. The 50%-duty repetitive pulses were produced by the reciprocal traveling wave in a pulse forming cable which was connected with a point-plane electrode gap in a water-cell. Laue plot of time lag distributions for the streamer initiation indicated that the initiation probability during the second pulse application became much higher than that during the first pulse application. We concluded that the change in space charges distribution due to internal field during the rest-time after the first pulse enhanced the streamer initiation probability at the second pulse application. Temporal development in the positive streamers during the repetitive pulse application was observed using a gated image intensifies. When the pulse was relatively high, the streamer discharges started the propagation at the first pulse and then the discharge channel became long step by step at the subsequent pulse applications. It was also found that the periodical emission due to excitation of OH radicals was detected for a long period after the development of the streamer discharge in a spectroscopic measurement.     

Enzymatic synthesis of novel oligosaccharides from L-sorbose, maltose, and sucrose using kojibiose phosphorylase

Glucosyl-L-sorbose, -maltose, and -sucrose were synthesized using kojibiose phosphorylase (KPase) from Thermoanaerobacter brockii ATCC35047 with beta-D-glucose-1-phosphate (beta-G1P) as a glucosyl donor. One disaccharide and two trisaccharides thus synthesized were isolated by Toyopearl HW-40S column chromatography. The results of KPase digestion, methylation analysis, and 13C-NMR studies indicated that these oligosaccharides were alpha-D-glucopyranosyl-(1-->5)-alpha-L-sorbopyranose, alpha-D-glucopyranosyl-(1-->2)-alpha-D-glucopyranosyl-(1-->4)-D-glucopyranose (4-alpha-D-kojibiosyl-glucose), and alpha-D-glucopyranosyl-(1-->2)-alpha-D-glucopyranosyl-(1-->2)-beta-D-fructofuranoside, which are all novel oligosaccharides. Glucosyl-L-sorbose was partially hydrolyzed to glucose and L-sorbose by alpha-glucosidases, while glucosyl-sucrose and glucosyl-maltose were not hydrolyzed by glucoamylase, alpha-glucosidases, or CGTase.     

Fluxless laser brazing of aluminium alloy to galvanized steel using a tandem beam – dissimilar laser brazing of aluminium alloy and steels

Tandem beam brazing with aluminium filler metal (BA4047) was conducted in order to develop the fluxless laser brazing technique of aluminium alloy (AA6022) to galvanized steels (GA and GI steels). Laser powers of tandem beam and offset distance of preheating beam from the root to the steel base metal were varied. Sound braze beads could be obtained by optimizing the preheating and main beam powers under the offset distances of 0–1 mm. A small amount of zinc remained at the braze interface between galvanized steels and the braze metal. The reaction layer consisting of Fe–Al intermetallic compounds was also formed at the steel interface, and the thickness of reaction layer could be predicted during the laser brazing (thermal cycle) process based on the growth kinetics with the additivity rule. The metal flow analysis of the melted filler metal on joints revealed that wettability and spreadability of the filler metal on the GI steel joint were superior to those on the GA steel joint. The fracture strength of the lap joint attained approx. 55–75% of the base metal strength of aluminium alloy. It was concluded that fluxless laser brazing could be successfully performed by using a tandem beam because the zinc coat layer acted as the brazing flux.     

Effect of grain size on heat affected zone cracking susceptibility.Study of weldability of Inconel 718 cast alloy (2nd Report)

Summary

It is generally recognised that the flux type of covered electrodes affects the profile and mechanical properties of welds and may well control the fatigue strength of fillet welded joints. Fillet welded joints, however, have seen few systematic investigations. The purpose of this investigation is to improve the fatigue strength of fillet welded joints through appropriate design of the covered electrode flux.

Ten types of covered electrode were trial‐manufactured with variation in the flux system at two levels (to improve the profile of the fillet toe region) and the added alloying element contents of each system at five levels (to vary the hardness of the weld metal). These covered electrodes were used to prepare non‐load‐carrying cruciform fillet welded joints using 570 MPa class high‐strength steel base metal. Fatigue tests (S = σ_max ‐ σ_min, σ_max = σ _Y ) were run with the fillet welded joints. The results obtained may be summarised as follows:

1. The profile of the fillet welds appears to be affected by the flux system and base metal but not by the added alloying elements.

2. The maximum stress concentration factor (K_max) is reduced to K_max ? 1.59 for covered electrodes using an MgCO₃‐MgO‐CaF₂‐iron powder system flux (M' series).

3. The fatigue strength of the fillet welded joints at 2 × 10⁶ cycles is improved to around 143 MPa in the M' series. It can safely be said that there is an inverse correlation between K_max in the toe region and the fatigue strength of the welded joints.

4. Appropriate relations are developed and used to calculate the recovery to the weld metal of added alloying elements. The recovery to the weld metal of the added alloying elements on average gives minima of around 98%Ni, 94%Mo, 85%Cr (which are good), and around 11%B.

     

Relationship between melt flows based on three-dimensional X-ray transmission in situ observation and spatter reduction by angle of incidence and defocussing distance in high-power laser welding of stainless steel

ABSTRACT

The objective of this research is to reveal relationship between melt flows and spatter reduction by angle of incidence and defocusing distance in partial penetration welding of an SUS304 stainless steel plate using a 6-kW power laser beam. In welding speeds from 50 to 250 mm/s, underfilled weld beads with spatters were obtained at more than 150 mm/s. According to the three-dimensional X-ray transmission in situ observation of melt flows at 150 mm/s in welding speed with tungsten carbide (WC) tracers, the melt flows achieved approximately 2.3 m/s in speed and made convex molten-pool surface behind a keyhole inlet grow higher, resulting in spattering over 0.1 mm in diameter. A 2 mm inner defocusing distance or a 20° angle of advance decreased the number of spatter over 0.1 mm in diameter by half or one-third in comparison with that at focal point and 0°. The X-ray transmission images demonstrate that the appropriate defocusing distance and angle of incidence made the speed of the melt flow decrease and the melt flow behind a keyhole inlet circulate, which led to not only suppressing the convex surface but also improving the frequency that the convex surface went back to the molten pool.     

Bacterial communities in petroleum oil in stockpiles

Bacterial communities in crude-oil samples from Japanese oil stockpiles were investigated by 16S rRNA gene cloning, followed by denaturing gradient gel electrophoresis (DGGE) analysis. 16S rRNA genes were successfully amplified by PCR after isooctane treatment from three kinds of crude-oil sample collected at four oil stockpiles in Japan. DGGE profiles showed that bacteria related to Ochrobactrum anthropi, Burkholderia cepacia, Stenotrophomonas maltophilia, Propionibacterium acnes, and Brevundimonas diminuta were frequently detected in most crude-oil samples. The bacterial communities differed in the sampling time and layer. Among the predominant bacteria detected in the crude oil, only three species were found for bacteria isolated on agar plates and were related to Burkholderia, Stenotrophomonas, and Propionibacterium, while Ochrobactrum sp. could not be isolated although this species seemed to be the most abundant bacterium in crude oil from the DGGE profiles. Using an archaea-specific primer set, methanogens were found in crude-oil sludge but not in crude-oil samples, indicating that methanogens might be involved in sludge formation in oil stockpiles.