Page 260 - Design of Simple and Robust Process Plants

246 Chapter 6 Process Design Based on Reliability
The reliability analysis was performed by the authors based on an analytical tech-
nique. The same calculations could be carried out using Monte Carlo simulations. In
the last case, different types of failures and its distribution on failure and repair rates
might have been introduced. The overall conclusions would not be any different, but
especially the impact of more specifically identified components and their failure
rates might provide a prioritized picture of causes of the failures and their impact.
The overall conclusions of the above application studies are that reliability engi-
neering tools are very useful in the quantitative analysis and support of design deci-
sions. The weak components with regard to reliability and availability are easily
identified. Often, technical solutions can easily be found or developed to increase
the reliability of these components.

6.5
Reliability, Availability and Maintainability (RAM) Specification

The purchase of equipment and supplies will, next to design specifications, at least
partly be accompanied by RAM specifications. These cover the quality of the equip-
ment in terms of reliability, availability, and maintainability. For supplies such as
power steam (and also other supplies), the RAMs cover the reliability and availability
of the supplies, as well as the reliability and availability of transportation of feed
streams and product streams.
The RAM data require a partnership between the supplier and the receiver, and
strong arguments exist for this statement:
1. The receiver is going to design and optimize his/her facility based on these data.
2. The supplier needs to optimize his/her facility on these data.
3. The data as such should be established in a realistic agreement as they rep-
resent a trade-off between the supplier and the receiver interest.
4. The agreed RAM data need to be realistic and supported by historic data.
5. An agreed measurement system must be established, especially as the data
are subject to fluctuations and require a minimum number of data points
over an extended time horizon. In this respect, a failure should be clearly
defined at this point.
The RAM specification should consist of the following items:

. Scope of the system;
± a description of the system
± the life time
± operating conditions
± failure cases
. Quantitative requirements
± availability
± failure rate
± time to repairs
± scheduled outages