Protection layers, definition

Protection layer definition Discussed in Clause 3.1.42 and Informative Clauses 4.2.3 and 4.2.4... 

This definition excludes inhibitor films or other corrosion-protecting layers such as paint and so on, which have the same function as passive films but a different origin. Such films are formed from components in the electrolyte (inhibitors) or are deposited in a technical process (e.g. cathodic deposition of paint). 

The fields marked Fe203 and Fe304 are sometimes labeled passivation on the assumption that iron reacts in these regions to form protective oxide films. This is correct only insofar as passivity is accounted for by a diffusion-barrier oxide layer (Definition 2, Section 6.1). Actually, the Flade potential, above which passivity of iron is observed in media such as sulfuric or nitric acid, parallels line a and b, intersecting 0.6 V at pH = 0. For this reason, the passive film (Definition 1, Section 6.1) may not be any of the equilibrium stoichiometric iron oxides, as is further discussed in Chapter 6. 

Ageing (see definition in Sect. 5.1) may limit the life span of geotextiles. Therefore sufficient stability must be available for the special fimc-tionality of the geotextile as a protective layer or as the geotextile component in the protective layer against the effects, which may cause internal... 

Independent protection layer In addition to conditional modifier and mitigating factor (influencing the likelihood of event), IPLs, which reflect the reliability of the protection layer, are responsible for performance of LOPA. In LOPA, the concept of the IPL is important, and should be well-defined and understood. CCPS definition of IPL is An IPL is a device, system or action which is capable of preventing a scenario from proceeding to its undesired consequence-independent of the initiating event or the action of any other layer of protection associated with the scenario. The effectiveness and independence of an IPL must be auditable. ... 

The system starts with project/process definitions and process conceptual design. The event history and application standards are applied to the conceptual design to obtain the process safety information. Now, the entire system is subject to PHA to obtain details about various consequences. After applying the available protection layer the situations are reassessed for SIF. As discussed earlier, target SIL assessments are also done. So, finally, all the following components form the SRS for SIS ... 

In Clause 4.0.2 of Chapter V, the necessary characteristics of independent protection layers (IPLs) were discussed. Definitions are given here again to elaborate further an understanding of the importance of assigning IPLs. The following are major issues ... 

The last two items above are very similar in nature and use formalized definitions of safety layers and protection layers to allow hazard study teams to allocate risk reduction factors to each qualifying layer of protection. 

As microprocessor-based controls displaced hardwired electronic and pneumatic controls, the impac t on plant safety has definitely been positive. When automated procedures replace manual procedures for routine operations, the probability of human errors leading to hazardous situations is lowered. The enhanced capability for presenting information to the process operators in a timely manner and in the most meaningful form increases the operator s awareness of the current conditions in the process. Process operators are expected to exercise due diligence in the supervision of the process, and timely recognition of an abnormal situation reduces the likelihood that the situation will progress to the hazardous state. Figure 8-88 depicts the layers of safety protection in a typical chemical jdant. 

After the inherent hazards are reduced, layers of protection are frequently used to protect the receptors of the hazard—the public, the environment, workers, other processes, or the process itself (Figure 1.1). In the strictest sense, one could argue that the definition of inherently safer applies only to elimination or reduction of the hazard. In the broad sense, the strength of a layer of protection can be improved by features that are permanent and inseparable from that layer. Thus, layers of protection can be classified into three categories, listed in decreasing order of reliability passive, active, and procedural. A passive layer of protection can be described as inherently safer than an active... 

Injection molding requires the barrel temperature to be about 350°C with a barrel pressure in excess of 138 MPa. The mold is maintained at 110°C to ensure uniform flow and high definition, and to discourage an uneven index of refraction, birefringence. The CD is about four one-hundredths of an inch (0.5 mm) thick. For prerecorded CDs, the PC is compression-molded on a stamper imprinted with the recorder information. This takes about 4 sec. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc. Then, a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic surface and the CD is complete. This process is described later in greater detail. 

On the other hand, the resistance of laminates with printed decor papers depends very much on the substance weight of the overlay paper used to protect the ink layers. There is a tendency, unfortunately, for an overlay to impair the definition of print and brightness of colour—which can be undesirable, or, particularly with more exotic designs such as metallized and pearlescent effects, even unacceptable. 

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