Piping components are the lifelines of industrial processes, transporting fluids and gases under a range of conditions. Ensuring their durability and reliability is paramount to the success and safety of any operation. In this article, we delve into the essential guidelines for selecting piping components to guarantee a minimum design life of 20 years.
Piping Components Selection for Refinery
a. A 20-Year Design Life
The foundation of a robust piping system begins with the assurance of a design life not less than 20 years. This ensures that investments in infrastructure pay off over the long term and that the system can withstand the rigors of operational demands.
b. Corrosion Allowance
In most cases, a minimum corrosion allowance of 1/8″ should be applied to process piping. This allowance accounts for the gradual material loss due to corrosion, extending the life of the components. However, exceptions can be made for clean hydrocarbon streams below 450°F.
c. Clean Hydrocarbon Streams
Clean hydrocarbon streams are those that operate above the water dew point, contain minimal free water, and have low levels of hydrogen sulfide (H2S) in the vapor phase. These streams, devoid of acidic or corrosive components like chlorides, sulfolane, carbon dioxide, amines, salts, or solids, may utilize a reduced corrosion allowance of 1/16″.
Materials Selection and Corrosion Rate
d. Corrosion Rate Estimation
The selection of materials for process piping should be based on an estimated corrosion rate not exceeding 6 mils per year. Reliable estimation methods, as outlined in technical modules provided in industry standards or those proposed by contractors and approved by relevant authorities, should be employed to assess corrosion rates accurately.
e. Utility Applications
For utility applications, a minimum corrosion allowance of 1/16″ is deemed sufficient, considering the typically less aggressive nature of these services.
f. Avoidance of A53 Low Silicon Pipe
In process applications exceeding 400°F, the use of A53 low silicon pipe is discouraged. However, a case-by-case evaluation should determine its permissibility in applications below 400°F, potentially necessitating positive material identification (PMI) checks with A106 carbon steel pipe.
g. ERW Pipe Restriction
Electric resistance welded (ERW) pipe is unsuitable for process applications due to its inherent limitations.
Joint Efficiency, Temperature, and Valve Trim
h. Joint Efficiency
All piping components, except castings, should possess a joint efficiency equal to 1, ensuring the structural integrity of the system.
i. Temperature Limitations
Carbon steel materials should not be utilized in environments exceeding 800°F, as their mechanical properties can degrade at such high temperatures.
j. Restriction on Ferritic or Martensitic Stainless Steels
Ferritic or martensitic stainless steels containing 12% chrome should not be used for pressure boundary materials, except in specific cases such as pump casings and valve stems.
k. Gasket Selection
Type 316 spiral wound gaskets with flexible graphite filler are the standard choice for gasket materials across various process streams.
l. Valve Trim
Valve trim selection should align with the specific application:
- API Trim 8: Standard trim for API 600 or similar valves.
- API Trim 12: Suitable for 300 series stainless steel piping, sour water with high ammonium bisulfide concentrations, rich amine, sulfolane, or other corrosive applications.
- Trim 5: Ideal for low alloy steels in high-temperature hydrogen applications, high-temperature streams exceeding 600°F, or high-pressure streams above 1500 psig. Special valves with superior metallurgy should match the valve body material and include at least half hard facing.
m. Materials Selection Table
To maintain transparency and accountability in the selection process, a materials selection table should document crucial parameters such as corrosion allowance, estimated corrosion rates, design life, and the technical module used for materials selection.
By adhering to these comprehensive guidelines, industries can ensure the longevity and reliability of their piping components, thus safeguarding their operations and investments for years to come.