Corrosion inspection program

Maintenance. The lack of maintenance and investment in inspection programs results in not only poor housekeeping but unnoticed leaks due to corrosion, leaking flanges and valves, and inoperative instmmentation that could prevent spills. 

Since HtS dissolved in water is very corrosive to carbon 4 steel, a comprehensive corrosion-control program is being conducted. In the field, each well is treated once per month by displacing inhibitor down to the perfora-. tions with stock tank oil. Corrosion coupons in the flow-lines are inspected every 6 months Little corrosion has been detected in the field. In the plants, corrosion in-hibitor is added daily to the gas-sweetening solvent, the salt water system, and the stabilizer overhead. Inhibitor is -Jj also added to bulk chemicals as received. Numerous corrosion coupons and probes are installed in each facility and are pulled for inspection every 1 to 3 months Corrosion rates have been low (less than I mil/year) asY result of the inhibitor injection program. 

Although the refrigeration of a hazardous process fluid will provide the benefits listed above, this technique does necessitate the insulation of the process equipment and piping. This makes it more difficult to inspect the equipment for external corrosion and embrittlement problems, unless there is an aggressive inspection program in place or noncorroding materials of construction are employed. 

The degree and frequency of external inspection of equipment and piping under insulation is site specific. The API 570 Piping Inspection Code has added this note of caution The extent of a Corrosion Under Insulation Inspection program may vary depending on the local climate warmer, marine locations may require a very active program, whereas cooler, drier, mid-continent locations may not need as extensive a program. [16]... 

A liquid pipeline has less stored energy than a gas pipeline, and a rupture does not cause an explosion. However, an explosion can occur on ignition of an explosive product. In the case of a hazardous liquid product pipeline, the environmental impact can be as serious as an explosion. The risk of an oil leak from the Trans-Alaska Pipeline System has continued to be the primary driver for the aggressive corrosion prevention and inspection program maintained by the operator. Of major concern is the risk of oil leakage into water streams and thereby contaminating water supplies. 

Corwith JR, Westermark RV. The downhole corrosion control program at Ekofisk. Inspection, Maintenance and Repair, Febr. 1984. 

The demonstrated reliability of these pipelines has required the use of several different corrosion protection schemes. To reduce attacks on the outer surfaces of pipelines, improved cathodic protection systems and coating materials (fusion-bonded epoxy, which replaced coal tar systems) have been used along with better inspection programs. 

Virtually all definitive test work is done in a pilot plant or plant. The final test is performance of actual operating equipment. A systematic, quantitative inspection program is the final measure of success of a corrosion control program. All other methods are evaluated in terms of how closely they approximate this method. Other methods used are listed and described briefly below. 

Even the best design cannot be expected to anticipate all conditions that may arise during the life of a system. Corrosion inspection and monitoring are used to determine the condition of a system and to determine how well corrosion control and maintenance programs are performing. Traditional corrosion inspection practices typically require planned periodic shutdowns or service interruptions to allow the inspection process. These scheduled interruptions may be costly in terms of productivity losses, restart energy, equipment availability, and material costs. However, accidental interruptions or shutdowns are potentially much more disruptive and expensive. 

Figure 6.1 Integration of corrosion inspection and monitoring programs for producing management information.

An example of an industrial concern being translated into an inspection program is the loss of plant profitability due to production losses associated with boiler tube failures. Underdeposit corrosion in steamgenerating systems is caused or enhanced by the breakdown of a protective magnetite film and/or the inability to form such a film. Production losses resulting from reduced steam capacity are far greater than the actual repair and maintenance costs incurred during shutdowns. The major contributors to the formation of deposits and scale are... 

In an idealized corrosion control program, inspection and maintenance would be applied only where and when they are actually needed, as reflected by the maintenance on demand (MOD) concept. In principle, the information obtained from corrosion monitoring systems can be of great assistance in reaching this goal. Conceptually, the application of a monitoring system essentially creates a smart structure, which ideally reveals when and where corrective action is required. 

Production losses during shut-downs are the major economic concern. The frequency of periodic shut-downs for maintenance and inspection depends on the rehabihty of the corrosion control program. The more corrosion control apphed, the fewer shut-downs will occur in the system. Thus, less time is lost from scheduled shut-downs. The frequency of costly, unscheduled outages can reduce even more drastically. 

VFO works well in gas turbines. In a nine-month test program, the combustion properties of VFO were studied in a combustion test module. A gas turbine was also operated on VFO. The tests were conducted to study the combustion characteristics of VFO, the erosive and corrosive effects of VFO, and the operation of a gas turbine on VFO. The combustion tests were conducted on a combustion test module built from a GE Frame 5 combustion can and liner. The gas turbine tests were conducted on a Ford model 707 industrial gas turbine. Both the combustion module and gas turbine were used in the erosion and corrosion evaluation. The combustion tests showed the VFO to match natural gas in flame patterns, temperature profile, and flame color. The operation of the gas turbine revealed that the gas turbine not only operated well on VFO, but its performance was improved. The turbine inlet temperature was lower at a given output with VFO than with either natural gas or diesel fuel. This phenomenon is due to the increase in exhaust mass flow provided by the addition of steam in the diesel for the vaporization process. Following the tests, a thorough inspection was made of materials in the combustion module and on the gas turbine, which came into contact with the vaporized fuel or with the combustion gas. The inspection revealed no harmful effects on any of the components due to the use of VFO. 

Insurance inspections and cleaning programs further add to the frequency at which a boiler may be out of service. During these outages and offline periods, the boiler metal waterside surfaces are especially susceptible to rapid corrosive attack and damage. Consequently, various protection protocols are employed to stave off this risk. The primary factors responsible for downtime corrosion are ... 

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