Visual external inspections

Visual external inspections (or in-service inspections) should be made regularly to operating vessels to help ensure the integrity of the vessel. The frequency of this inspection should... 

Visual external inspections are often made with the normal physical limitations of accessibility and visibility that exists at the time of the inspection. Normally, for the removal of insulation, scaffolds or man-lifts are not employed during frequent external inspections unless tell-tale conditions warrant a closer examination. In those cases, the difficulty of access to any portion of the tank should not be permitted to prevent a thorough inspection. 

Visual external inspections (or in-service inspections) should be made regularly to operating vessels to help ensure the integrity of the vessel. The frequency of this inspection should be site-specific, between semiannually and once every three years for most chemical plant processes, depending on the aggressiveness of the chemical plant atmosphere. However, API 510 will accept intervals up to once every five years. 

The plant management should allocate in writing the responsibihty for receiving on the site any materials, spare parts and components, and should issue a special procedure to control the receiving and acceptance process. This procedure should include visual external inspection for transit damage or deterioration, and verification... 

Inspections must be determined and carried out by competent persons. An inspection will vary from a simple visual external inspection to a detailed comprehensive inspection which may include some dismantling and/or testing. However, the level of inspection would normally be less than that required for a thorough examination under, for example, LOLER for certain items of lifting equipment. 

DOT and TC state that results of required periodic inspections of a cylinder must be recorded, and a copy kept by the owner or the owner s authorized agent either until the expiration of the retest period or until the cylinder is again reinspected or retested, whichever occurs first [1, 2]. Also, a cylinder that passes the re-qualification procedure must have the date permanently stamped on the cylinder in the prescribed manner. Note An E is to follow the date (month and year) when requalification by the visual external inspection method is allowed in lieu of hydrostatic retesting. 

Interior corrosion is best evaluated by a hydrostatic test combined with careful visual inspection. Thickness-measuring and flaw detection devices of the ultrasonic type may be used to evaluate specific conditions. Basic corrosion limits for both low and high pressure steel cylinders were discussed under the External Inspection section of this chapter. 

Before first use hoses to be inspected visually internally and externally and tested at proof pressure. Repeat at least annually and include check on electrical resistance. The resistance of the complete assembly should be not more than 15 ohms, unless the hose is intended to be non-conducting when resistance should be at least 25 000 ohms. Inspect hose daily when in use. Hoses used at monobuoys should also be hydraulically tested. 

The green colour due to the Cr3+ ions formed by the reduction of potassium dichromate makes it impossible to ascertain the end-point of a dichromate titration by simple visual inspection of the solution and so a redox indicator must be employed which gives a strong and unmistakable colour change this procedure has rendered obsolete the external indicator method which was formerly widely used. Suitable indicators for use with dichromate titrations include AT-phenylanthranilic acid (0.1 per cent solution in 0.005M NaOH) and sodium diphenylamine sulphonate (0.2 per cent aqueous solution) the latter must be used in presence of phosphoric) V) acid. 

On pressurized tanks, the seal has to be frictionless and useful over a wide range of pressures, temperatures, and corrosion conditions. Displacement detectors can be magnetically coupled, or they can use a torque tube, diaphragm and force bar, spring balance, flexible disk, or the flexible shaft design. All of them can be used to detect a liquid-vapor interface, a liquid-liquid interface, and if the level is constant, they can detect density as well. The external displacers are usually installed with level gauges (Figure 3.117) so that the operator can visually inspect their calibration and performance. 

Expansion joints Visually inspect externally for exceeding misalignment specification Correct or replace as needed Internal inspection every year Replace or upgrade as needed ... 

Most of the cmstaceans consumed as aquatic food belong to the classes of shrimps, prawns, crabs, and lobsters. Several hundred crustacean species are used for human consumption, and species assignment by visual inspection after removal of external features is extremely difficult. Authentication of crustaceans has been performed by just the same PCR-based techniques as those used for fish, including RFLP and SSCP analysis. In the analysis of shrimps, intraspecies variability of DNA profiles has to be considered (Figure 11.2). In most studies the mitochondrial genes 16S rRNA and cytochrome oxidase I was used as a template. Some recently published studies on differentiation of shrimps are compiled in Table 11.1. 

Visual inspection is best suited in rapid, noncontact survey of. specific areas and is ideally followed by more sophisticated methods to determine the extent of visual damage. Visual inspection is an important and simple technique by which gross defects, discoloration and external corrosion can be identified. The efficiency of such visual tests can be improved by the use of facilitating tools such as a light source, a magnifying glass, and a horoscope. Other apparatus are also available such as the profile projector of Walker and McKelvic [30], Used to examine complex parts, this instrument has a resolution of 2.5pm. 

A certified renovator must visually verify the cleanup in any external areas, including the ground and any exterior windowsills. Alternatively, if the owner or any law requires dust clearance sampling, that can substitute for the visual inspection. The renovator must re-clean if any dust or debris remains. ... 

A particularly dangerous breach in a pressure vessel happened in a steam generator where a crack (about 70 per cent of the circumference with a depth equal to a significant fraction of the thickness) was discovered on a circumferential weld. At some points the crack was through wall . It was discovered during a visual inspection thanks to the humidity patch on the external insulation layer of the component. 

Challenge In all systems with rope operation Hke ropeways or mining shafts it is usually necessary to visually check the ropes regularly for external damages. The rope has to be watched by several employees at very low speed while they are trying to detect damages. This inspection is very time-consuming and the inspection results are often neither reliable nor documented. 

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