Materials Selection – Reliability and Safety

The likelihood and consequences of a failure must be considered in the selection of pressure vessel materials. Consideration of these factors may lead to conclusions on materials and corrosion allowances that differ from these minimum guidelines.

Each individual case warrants consideration of these factors, and judgment is then necessary to choose economical materials.

Various factors to consider include the following:

Likelihood of failure:
1. Past history in same or similar services.
2. Whether onstream inspection can predict failures.
3. Shutdown frequency.

Consequences of failure:
1. Personnel safety: acids, caustic, H2S, HF, etc.
2. Fire hazards: LPG, high pressure H2, proximity to furnace.
3. Lost production (plant profitability).
4. Ease of repair or replacement.
5. Geographic factors: availability of expert craftsmen and replacement material.
6. Will leakage cause catalyst poisoning or affect plant performance?
7. Will plant be shut down, or can equipment be bypassed?
8. Will plant shutdown force related plant shutdowns?
9. Will leakage cause environmental problems such as pollution of navigable waters?

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