Paper deterioration factors

Many conservation treatments have been devised to slow down the rate of deterioration of paper. Often these treatments neutralize excess acidity in paper, which is an important factor in paper permanence. The probability of success with a new method is often determined by the use of accelerated aging tests and also by drawing parallels with existing methods thought to be effective. Many studies have investigated the best conditions for accelerated aging tests, but disagreement between laboratories is often found. However, even the best set of conditions produces a distortion of the results that would have occurred in ambient conditions. 

The lack of paper permanence is attributable to both internal and external influences [4]. In addition to sizing materials, internal factors include the type of fiber, coatings, and the presence of acidic and metallic compounds. External variables are the conditions during storage and use. Heat and humidity accelerate the deterioration of paper, and atmospheric pollution is frequently the source of external acid attacks. A comparison of identical volumes stored in the Netv York Public Library and the Royal Library in The Hague proved the importance of proper storage, as the New York books were found to be in a far more advanced stage of deterioration [5]. 

The potential permanence is built into paper at the time of manufacture it is determined by the materials used and the processes of manufacture. Three important factors are recognized (1) deterioration of the cellulose fibers prior to manufacture into paper and the presence of noncellulose components (2) the introduction of additives (sizing, loading, etc.) to the papermaking stock and (3) the presence of deleterious impurities originating from the fiber furnish, additives, process water, and mill equipment. 

Dr. Amalio Gimeno, another scientist, was probably one of the first to discuss the physical and chemical causes of book deterioration. In 1932, during a presentation before the Spanish Academy of Exact, Physical, and Natural Sciences that he called "Pathology of the Book, he listed the factors that caused deterioration as dust, humidity, excessive temperature, fireplaces, and gaslights (4). Also, he accused the paper industry of planting the seed of destruction in their products and cited a study made in 1924 by the Central School of Industrial Engineers on... 

A much more recent development is the morpholine process in which fifty books per hour are treated in an evacuated chamber with morpholine-water vapor (12). In its present form, it was effective on 95% of the papers treated, prolonging their life on average by a factor of 4-5 (Figure 7). Though it does not leave a titratable alkaline reserve in the paper, acid papers treated in this manner aged in the presence of 5 ppm S02 at 75 °C and 60% relative humidity deteriorate more slowly than if untreated. Recent tests of twenty treated books at the Library of Congress show that their pH has not declined in two years. The equipment for the process was set up in the Virginia State Library where 35,000 books were treated in the first seven months of operation. 

Acidity has long been recognized as a major factor contributing to the deterioration of cellulose-containing materials. In an effort to combat the harmful influence of acidity, researchers have developed a variety of deacidification techniques capable of decreasing the acid content of most paper-containing objects that are found in museums and libraries. These techniques often are used by conservators in the care of books and works of art on paper (I). Nevertheless, the nature of the chemical processes that cause papers to yellow and to lose strength remains somewhat obscure, and the role of acidity in these processes also is not well understood. 

The prime factor in choosing an abradant is its relevance to service, but it also has to be available in a convenient form and, for anything but ad hoc tests, it is essential that it be reproducible. In consequence of these considerations, abrasive wheels and papers or cloths predominate where cutting by sharp asperities is to be simulated. The abrasive wheel is probably the most convenient, because of its low cost, its mechanical stability, and the ease with which it can be refaced to maintain a consistent surface. Abrasive papers and cloths are cheap and easy to use but are not so readily refaced and will deteriorate in cutting power more quickly. Although basically low in cost, both wheels and papers are a considerable c.xpense when bought as standard reference materials. Materials such as textiles or smooth metal plates are more relevant for some applications, but they abrade relatively slowly, and if conditions are accelerated they give rise to excessive heat buildup. 

As seen in Section 1, Kijima Nakagawa (1991) proposed a cumulative damage shock model with imperfect periodic maintenance actions. Each action reduces the deterioration level by 100(1 — b)% of total damage, where b 6 [0,1]. The same authors introduced in Kijima Nakagawa (1992) an improvement factor t. The amount of damage after the preventive maintenance becomes bi Yi when it was T) before the maintenance action. Moreover the imperfect maintenance action can impact the failure rate of the system, this method is called the improvement factor method . This concept had been introduced by Malik (1979). Nicolai et al. (2009) consider different imperfect maintenance actions which have a random impact on the deterioration level of the system. A random improvement according to the residual time on a finite horizon is rarely considered, that is why, in this paper, such a random improvement is considered. 

This paper focuses on how to model the deterioration of static pressurized process equipment to enable efficient inspection and maintenance planning. Such equipment tends to gradually deteriorate over time from erosion, corrosion, fatigue and other mechanisms, and at some point of time inspection, repair or replacement is expedient with respect to safety, production and costs. The deterioration of the equipment is influenced by many factors such as type of equipment, system design, operation and process service, material and environment. For hydrocarbon systems, the most critical deterioration mechanisms are corrosion due to CO2 and H2S, microbially influenced corrosion, sand erosion and external corrosion (DNV 2002). In general, CO2 is the most common factor causing corrosion in oil and gas system of low alloy steel (Singh et al. 2007). 

As indicated by e.g. Allamilla Sosa (2008) and NORSOK M-506 (2005), there are reasons to believe that the lack of knowledge and uncertainty in the influencing factors in the field is the main contributor to the imcertainty in the prediction of the deterioration. With other words, the uncertainty in z(f) will be much larger than the uncertainty of g(), hence we will start to focus on the uncertainty in z(i). Melchers (2005) suggests that even if all test samples in a corrosion experiment are exposed to the same environment, a random behavior ofX f) is experienced. In this paper we suggest to explain this randomness as a result of an unknown z, such that this situation is a variant of the second condition. 

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