Gamma ray scanning

The current and past operation should be compared so that the timing of the observed problems is estabhshed. The possible causes (hypotheses) can be compared against the measurements found on the log sheets. The number of possible causes can then be reduced. When the quantity or quahty or measurements is insufficient to further reduce the set of causes, additional measurements are required. These may require special instruments (e.g., gamma-ray scanning) not routinely usedin the plant. Alternative operating conmtions may also be required to further reduce the number of causes. As part of the problem identification, it is alwavs important to look for measurements that are inconsistent with the proposed explanation. They will be more informative than the ones justifying the hypothesized cause. Ultimately, with appropriate additional measurements, the cause can be identified. This is not an exact science and, as stated above, relies heavily upon the communication, technical, and investigative skills of analysts. 

Figure 8-56. Examples of gamma ray scanning diagnostic diagnosis of depropanizer column to evaluate performance. Used by permission, Tru-Tec Division, Koch Engineering Co., Inc.

Profiles of foam density, derived from gamma ray scans of the separators, showed that no discrete foam layer was in the vessels, but a two-phase mixture of gas and liquid occupied a substantial pan of the total height of the vessel. 

Permanent gamma ray scanning equipment was installed on each separator along with foam density and level recorders in the process control room. An emergency trip system that automatically shuts a valve in the appropriate separator gas line to isolate the separator from the compressor suction drums when a high foam level occurs was added also. A similar trip system was insulted in the gas feed line from the HP separator to the power station... 

With the above equipment, it was demonstrated exptly that a 30-mil (0.030,f) gap can be detected using rigidly controlled lab conditions with a mock projectile and an artificially induced separation. This technique was also tested with 100 fully loaded projectiles. The presence of an actual base separation was not positively identified in this very small sampling of shells. However, two projectiles showed abnormal gamma-ray scan profiles. Upon sectioning, these indicated the presence of anomalies at the base region. The method is concluded to be sufficiently sensitive to detect... 

A gamma-ray scan of the column can generally pinpoint problem areas or zones. The rays penetrate the column metal, and their absorption depends on the amount of fluids or solids in then-paths. Several commercial organizations specialize in scanning, and they are capable of traversing the entire colnmn, with rays emitted in several different directions. 

An additional point of inflection (Fig. 14.11c0 on a downcomer gamma ray scan (33). On a tray gamma ray scan, foaming resembles flooding, but may appear somewhat less dense. 

Figure 14.14 illustrates the principle of column gamma-ray scanning. The source and detector are lined up on the same horizontal plane, and a reading is taken either across the tray or across the... 

Premature flooding occurred due to foaming in downcomers fh>m just below the feed up. This was detected by gamma-ray scans. Adding antifoam improved performanoe but was imdesir-able in the process. Downcomer enlargement in the trouble area solved theproblmn. 

C26.10 Cl 133-96 Standard Test Method for Nondestructive Assay of Special Nuclear Material in Low Density Scrap and Waste by Segmented Passive Gamma-Ray Scan... 

Gamma Scanning is a very effective, well established, troubleshooting technique. This powerful diagnostic tool, which has been used for decades, has become popular as it allows inspection of the distillation column components without interrupting operation In comparison to other non-destructive control techniques used in practice, gamma-ray scanning provides, in real time, the clearest vision of the production conditions inside a process reservoir. It is also cost-effective, particularly when compared to lost production (Hills, 2001). 

Developments on software tools for data acquisition and numerical simulation for Gamma-ray scanning, IEEE Proceedings of the 1st ANIMMA (International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and their... 

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