Stress Analysis Of Column Piping System - 01

          Columns are one of the principal equipment of any processing plant. Columns are cylindrical steel vessels that are used for distilling raw materials in the production of such products as gasoline, diesel, and heating oil. Looking to the construction of column, it has number of trays at different elevation. Temperature at each tray location differs based on process. This article highlights column modeling in CAESAR-II and stress analysis procedure for column connected lines. Same procedure can be adopted for Reactor line, Stripper line stress analysis.

REQUIRED DOCUMENTS FOR COLUMN LINE ANALYSIS

♦ Column G.A. drawing with all dimensions, nozzle orientation, materials etc.

♦ Column temperature profile.

♦ Line Designation Table/ Line list/Line Parameters and P&ID.

♦ Column line ISO.

♦ Allowable nozzle load for column as specified in project.

 Column nozzle is checked for axial force, circumferential moment and longitudinal moment. Nozzle in skewed direction is checked for axial force and resultant moment.

Column Temperature Profile.

           Different organization uses different methods for creating column temperature profile.Generally, Single OPE and DEG temperature case is considered from Mechanical Data Sheet for Column. This is the most conservative approach. 

          But sometime, in large bore piping, huge nozzle load is created by this conservative method, hence we can use following any of these two methods for Stress Analysis by creating temperature profile of column. Different organization uses different methods for creating column temperature profile.  Here I will describe two methods which are most widely used.

Average Method: 

Following Procedure is used for this method;

1. Identify and Mark the nozzle size from P&ID which will make considerable impact in column temperature. Generally, big size process nozzle is considered in it. Instrument Nozzle, utility Nozzles, Small Bore Nozzle and Manhole are not considered.
2. Identify the operating temperate of pipes connected to two beside nozzle.
3. Take average operating temperature of these two lines.
4. Assigned same average temperature to the column portion between this two Nozzle.
5. Repeated the same step for other temperature case Egg. DEG Case.
6. For Skirt temperature is calculation, please follows link : Skirt Temperature/Expansion Calculation

Let’s assume that there are five big size (N1, N2, N3, N4 and N5 as shown in Fig.) outlet nozzles in a typical tower. So, temperature profile for that column can be created as shown in Fig.

Operating Case Temperature Profile is as following;

OPE Case Temperature Profile by Average Method

Design Case Temperature Profile is given as following;

DEG Case Temperature Profile by Averaging Method

            After considering all process line temperature, A master column C-II model is generate which can be used in all different stress system connected to same column.
For particulate system, No need to attached Nozzle and Pipe Model which are not the part of same system. Hence, final column model for our stress system is show in following picture.

 Links for Reference articles: 

• Stress Analysis Of Column Piping System – 02
• Skirt Temperature/Expansion Calculation
• Piping & Column Modeling in CAESAR-II
• Procedure for Pump Modeling