The overall vibration characteristics of the 60in flare header piping system, based on the first 15 modes, suggested concerns regarding the presence of maxima / minima and ‘Point of Inflections’ on the 60” section of the main header in the vicinity of Node-3383, which is location of actual failure that occurred during the failure incident. The current configuration of the sulfur lateral branch was also found to provide restraint to the 60" header, such that it is believed to impose unfavorable modes characteristics at the location of actual failure that occurred during the failure incident.

Mechanical vibration analysis is part of a Design Approach 3 of API 618, 5th edition. The scope includes calculating Mechanical Natural Frequencies (MNFs) throughout the system and a Forced Response Analysis to predict vibration and stress amplitudes, if necessary.

Accurate FE modeling, including
“super‐element” compressor frame

Reformer Piping Stress Analysis

"STRESS OF LARGE DIAMETER PIPING SYSTEM SHOE SUPPORT"
Proceedings of the ASME 2017 Pressure Vessels & Piping Division Conference, PVP2017, July 16-20, 2017, Waikoloa, Hawaii, United States.

FIG.1 TYPICAL SHOE SUPPORT

FIG.2 SYMMETRY AND MESHED FINITE ELEMENT
MODEL

TOTAL STRESS INTENSITY FOR D/T=200, WRAP
ANGLE 120°, AND b/D=0.5 SHOE SUPPORT

STRESS INTENSITY OF ELASTIC-PLASTIC
ANALYSIS RESULT FOR LOCAL FAILURE EVALUATION

EQUIVALENT PLASTIC STRAIN PLUS COLD
FORMING STRAIN OF ELASTIC-PLASTIC ANALYSIS
RESULT FOR LOCAL FAILURE EVALUATION

LIMITING TRIAXIAL STRAIN FOR ELASTICPLASTIC
ANALYSIS RESULT FOR LOCAL FAILURE
EVALUATION

ASME-B31J-2008-Test Method for Determining Stress Intensification Factor

PVP2015-45378"Stress Intensification Factor for Large Diameter Welding Tee Connections"
Proceedings of the ASME 2015 Pressure Vessels and Piping Conference, July 19-23, 2015, Boston, Massachusetts

Static Method of Wind Analysis of Piping systems in Caesar II using Pressure Vs elevation Method

Wind load is an occasional load which normally occurs less than 20% of plant operating time. There are two methods for wind analysis-Static and Dynamic.

Criteria for selection of lines for Wind Analysis:
Criteria should be mentioned in ITB document. As a guideline the following can be followed after verification from client:
• Lines with outside diameter 16” and larger (including insulation) running on 10 m and above.
• Steam / Flare header on the pipe rack.
• Other lines considered important as per stress engineer’s decision.
However if lines are covered by some shelter or other structures then wind analysis can be ignored for those lines.