Inspection for corrosion

Bases should be inspected for corrosion and corrected if necessary. 

If different materials are used in different sections of the column, special care must be taken to ensure that no interchanging of materials occurs between sections. If the column has previously been in service, its internals should be inspected for corrosion and operation damage. The materials of any parts that were changed should also be checked. 

The hoist must be carefully inspected for corrosion and damage especially if the hoist has been out of service for a prolonged period of time. Hoists located in wet underground hoist rooms are particularly at risk of heavy corrosion and metal pitting after only a few years if they have not been in continuous operation and fully serviced, as seen in Figures 4 and 5. The pictured hoist was overhauled and re-commissioned at a new mine site as shown in Figure 6. The unanticipated corrosion repairs contributed to a budget overrun. 

Be aware and inspect for corrosion under pipe supports and corrosion under insulation. Promptly handle any deficiencies. 

Regular inspection for corrosion data, pressure vessel, etc. 

Cost reductions for scheduled maintenance and inspections for corrosion and fatigue cracks. 

Internal corrosion of the down-comer pipe is a common problem. Build-up of sediment on the walls or bottom of the treater can cause the interface levels to rise and liquid to carry over and/or oil to exit the treater with salt water. Bi-annual inspections should be performed to include internal inspection for corrosion, sediment build-up, and scale build-up. 

The IP s were used in combination with appropriate Pb-filters (see 121). For wall thickness inspection we used standard medical IP s (AGFA MDIO), which exhibited an inherent unsharpness of ca. 310 pm. This should be compared with the inherent unsharpness of the film for an Ir-192 exposure which amounts 230 pm 111. For corrosion assessment we used IP prototypes with an inherent unsharpness < 230 pm. 

Projection radiography is widely used for pipe inspection and corrosion monitoring. Film digitisation allows a direct access to the local density variations by computer software. Following to a calibration step an interactive estimation of local wall thickness change based on the obtained density variation is possible. The theoretical model is discussed, the limitations of the application range are shown and examples of the practical use are given. The accuracy of this method is compared to results from wall thickness measurements with ultrasonic devices. 

Projection radiography has long been used for pipe inspection and corrosion monitoring. In this traditional tangential wall thickness estimation the distance of border lines of the projected wall shadows of a pipe onto the film is a direct measure for the wall thickness. This method is not considered here, newer developments can be found in / /. 

LORUS is also used for inspection of piping that has been on supports or sleepers for some time, to see whether corrosion has developed at the contact points. But the technique can also be used for corrosion detection under insulation, inspection of pipelines at dike and road crossings, nozzle reinforcement pads or craek detection in suspension systems for railway cars. 

Metals and alloys do not respond alike to aU the influences of the many factors that are involved in corrosion. Consequently, it is impractical to establish any universal standard laboratoiy procedures for corrosion testing except for inspection tests. However, some details of laboratory testing need careful attention in order to achieve useful results. 

The manuals provided by the equipment manufacturers should indicate the recommended preventive maintenance tasks and the frequency they should be performed covering such aspects as cleaning, adjustments, lubrication, replacement of filters and seals, inspections for wear, corrosion, leakage, damage, etc. 

Underground tanks are not recommended for plant areas. They cannot be inspected for external corrosion, and the ground is often contaminated with coiTosive chemicals. 

All storage tanks should be scheduled for inspection every few years. And on insulated tanks the insulation should finish 200 mm above the base so that checks can be made for corrosion. 

Another tool the interstates use to maintain their pipelines is a device known as an intelligent pig. Propelled through the pipeline with the gas stream, these devices, taking thousands of measurements with electronic sensors that can be analyzed later by computers, can inspect pipeline interior walls for corrosion or other defects and remove accumulated debris from a section of pipeline. Pipelines also use state-of-the-art coating and cathodic protection to battle corrosion. 

If changes have been made to the process (e.g. if incoming water quality cannot be maintained or other uncertainties arise concerning the corrosion behavior of the construction materials) it is possible to incorporate coupons or probes of the material into the plant and monitor their corrosion behavior. This approach may be used to assist in the materials selection process for a replacement plant. Small coupons (typically, 25 x 50 mm) of any material may be suspended in the process stream and removed at intervals for weight loss determination and visual inspection for localized corrosion. Electrical resistance probes comprise short strands for the appropriate material electrically isolated from the item of plant. An electrical connection from each end of the probe is fed out of the plant to a control box. The box senses the electrical resistance of the probe. The probe s resistance rises as its cross-sectional area is lost through corrosion. 

The removal of rust films or other corrosion products to facilitate inspection for perforation prior to termination of the exposure will change the natural performance of the material, and is therefore not tolerable. 

No one method for corrosion inspection is sufficient in itself and it is extremely dangerous to rely on data provided by one method only. A study is required of all methods available and the most suitable then chosen —... 

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