ASME B31.3 Process Piping is one of the most commonly used design and construction codes for the piping in process plants.  This code today covers what was originally envisaged as 3 separate codes:
  • B31.3 Petroleum Refinery Piping
  • B3.6 Chemical Plant Piping
  • B31.10 Cryogenic Piping
B31.3 was originally developed to serve refineries which in general have low pressures, high temperatures, liquid flows and the piping material is mainly carbon steel.  LNG plants often have much higher design pressures, lower (sometimes cryogenic temperatures), gas flows and a lot of stainless steel piping. Traditional B31.3 pipe stress analysis focuses on checking whether the system has sufficient flexibility to handle thermal expansion.  Formal equations to check longitudinal stress due to sustained and occasional (mechanical) loads were only formally introduced into B31.3 in 2010. However, there many potential failure modes and design cases for which B31.3 does not provide any explicit rules or guidance.  Instead the quantitative assessment if left up to the engineer by the use of phrases such as "shall be taken into account" or "shall be considered".  Some examples are:
  • Vibration
  • Dynamic loads such as fluid transients
  • Thermal bowing
  • Fatigue
  • Local stresses due to attachments such as pipe shoes
Evaluation of a failure mode without a well defined set of rules means that each case needs to be examined based on its particular circumstances.  The consequences of a loss of containment will usually play a role in determining which methods are used. An assessment may be anything from exercising engineering judgement to finite element analysis.  When finite element analysis is used B31.3 prescribes ASME VIII Division 2 Section 5 methods.