Inherently Safer Piping – Best Practices

This paper presents lesser known items in the upstream and midstream industries important to piping stress and overpressure protection.

Compared and contrasted items in the ASME piping codes B31.1/3/4/8 include corrosion allowance, equations, manufacturing tolerance, material choices, maximum allowable pressures, overpressure protection devices, stress values and thread depth. Equations in the codes are adjusted for factors not present in the codes. Calculation results are presented to show the impact of taking all factors into account and the different results for the same system using each code. Inspection, testing and maintenance of over pressure protection devices are discussed. The implications of B31.8 references to B31.1 for water and steam and B31.3 for air, lube oil and hydraulic power are discussed. Many times design pressures are set below the code minimum design pressures, so those are presented for steam, feedwater, blow piping and drains.

Items outside the ASME piping code that should be taken into account, such as surface dead loads, surface live loads, and cyclic loads on buried pipe fatigue are also presented. Failure mechanisms, equations, and acceptance criteria for deflection, ovality, through wall bending, crushing, ring buckling, fatigue, longitudinal, thermal expansion and fluid transients are described. Sources of this information are API Recommended Practice 1102, Steel Pipelines Crossing Railroads and Highways and American Lifelines Alliance, Guidelines for the Design of Buried Steel Pipe. 49 CFR 195 and 49 CFR 192 are also discussed.

Using these presented methods results in inherently safer piping and safer pressure relief system design.