ASME B31.3 is the governing code for process piping on most reciprocating compressor installations, but several of its requirements are frequently misapplied or overlooked in compressor piping design. Here are the most common areas where compliance gaps occur.
Dynamic Loading is Not Optional
ASME B31.3 requires that piping systems be evaluated for all applicable loads, explicitly including dynamic loads such as those induced by reciprocating equipment. The code does not specify a particular method for this evaluation, but API 618 fills that role by providing the industry-standard methodology.
In practice, many piping stress analyses for compressor installations are performed as static-only analyses, with dynamic loading either not evaluated or evaluated using highly simplified methods. This is not compliant with B31.3 when dynamic loading is a credible concern — which it always is for reciprocating compressor piping.
Small-Bore Fatigue Evaluation
B31.3 requires that all piping components, including small-bore connections, be evaluated for fatigue when cyclic loading is present. The code provides a fatigue screening procedure and, where screening indicates fatigue is a concern, requires a more detailed evaluation.
This requirement is almost universally ignored for small-bore instrumentation connections on compressor piping, which is why small-bore connection failures are so common.
Weld Quality Requirements
B31.3 specifies minimum weld quality requirements including radiography and inspection levels that depend on the severity classification of the service. Compressor discharge piping in high-pressure gas service is typically Normal fluid service at minimum, and may be Severe Cyclic if the fatigue evaluation indicates high cyclic stress.
Socket welds, which are commonly used for small-bore connections, are not permitted in Severe Cyclic service under B31.3. This is a frequently violated requirement in compressor installations where small-bore connections are routinely made with socket welds without a fatigue evaluation that would identify the appropriate weld category.
