A shell and tube exchanger is operating with an inlet temperature of almost 900 degree Celsius with a short time from a cold start. The gasket around the tubesheet started leaking after a few of these starts. Red-Bag has executed the analysis of the problem in cooperation with partner Wentzel Dynamics. A FEA model was made for the mechanics of the tubesheet and the flow was implemented to predict the correct thermal effects. The overall FEA investigation was a mulit physics quest. The result was that due to the large temperature difference the thick tubesheet started to change shape. Instead of a flat tubesheet the tubesheet became convex shaped. Due to the rotation at the end of the tubesheet gasket facing changed and would deform the gasket. Suggestion have been made to prevent the enormous temperature shock in the heat exchanger.

Shell and tube heat exchangers are complex equipment. The tubesheet is facing on both sides different design conditions and also during start-up different conditions occur. The mechnical model and calculation codes require the engineer to assess the various conditions. Designing a heat exchanger requires experience of the do's and dont's. High pressure differences and high temperture differences at both sides of the tubesheet make heat exchanger design a challenging task. Red-Bag has provided the engineering service to calculate the already designed cover flange and the combination with the gasket at high pressure. Small modifications have been implemented for a successful pressure test. (Exotech)

Red-Bag has calculated many pipe class flanges. The pipe class consists of various piping components, ranging from pipe, all sorts of fittings up to flanges. The flanges are usually the limiting factor, since the flange rating is used as the design condition for the pipe class. The strength limitation of the flange is therefor covered, however the leak tightness of the flange assembly (flanges, bolts, gasket) is not further determined. The bolt load will to a large extend determine the overall quality of the flange assembly. Red-Bag does the flange calculations for example according the EN 1591-1 to obtain the required bolt load for the design conditions and the required leak tightness. The bolt load table and assembly requiremnts are added to the pipe class and is therefor consistent with the quatlity requirements for the welding work. (work done for Borealis and Vopak)

Flanges in and on equipment are calculated according the various calculation codes. The calculation codes such as the ASME VIII div.1, the EN 13445-3 or the EN 1591-1 have a different approach and different assessment criteria. For critical equipment and equipment flanges Red-Bag can execute all these calculations and compare the different results. Based on the strength assessment and the leak tightness assumptions has provided valuable information and suggestions to mitigate troubeled flanges. Manholes on storage tanks have usually a large diameter and a thin flange and cover. The internal pressure is relatively low and the temperatures are ambient. But after years of operation it occurred that the manhole flanges started to show problems. The general assumptions was that the bolt load should be increased but this did not solve the problem. The problem remained and additional problem was that the bolts and manhole were overloaded. Engineering services were provide by Red-Bag resulting in new bolt load and design parameters. (Vopak)

The flange assembly with the bolts/nuts, washer, gasket and flange pair is a mechanical complex assembly. Existing calculations are mostly based on the Taylor Forge method looking at the allowable stress in the flange and bolts. Only a few (static) parameters are used to take the gasket behaviour into account.

A more detailed calculation method is the EN 1591-1. The calculation approach is more detailed and considers the behaviour of all components. The gasket for example is ....

The calculation will also give some indication of the expected leak tightness of the flange assembly ...

Piping ...

Equipment ...

To be continued ...