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CB&I

CBI-Lummus

Coke Drum Innovation

Chicago Bridge & Iron Company (CB&I) has fabricated, erected and repaired Coke Drums for over 50 years. CB&I is well aware of the problem of bulging and cracking in the vicinity of the circumferential weld seam experienced with many Coke Drums. These bulges and cracks are due to the severe operational thermal cycling often experienced in Coke Drums over the life of the vessel.

chicagobridge.com

Coby Stewart
cstewart@cbiepc.com
(832) 513-1636 phone
(713) 466-3182 fax

CB&I Worldwide Administrative Office
One CB&I Plaza
2103 Research Forest Drive
The Woodlands, TX 77380, USA
(832) 513-1000

Chicago Bridge & Iron Company N.V. Corporate Headquarters
Oostduinlaan 75
2596JJ The Hague, Netherlands
+31 70 373 2010


Background

For many years there have been ongoing studies to find ways to lengthen Coke Drum operating life. Thermal cycles occur during filling with hot (approx. 900 ° F) product and during water quenching after the coke has formed. As the surface of the fluid (product or water) rises, a severe moving thermal gradient occurs in the vessel shell as the fluid (hot or cold) is pumped into the vessel.

Thermal and stress analyses of this condition show that the higher strength weld metal in circumferential seams has a stiffening effect which increases stresses leading to distortion and cracking. The effect is similar to having a bellyband around the vessel. Vertical welds do not introduce the same problem since there is a continuity of metal properties in the vertical direction. In order to address this effect, some Coke Drum specifications have required that weld metal yield strength be within a close percentage of base metal yield (e.g. 10%). Because of the many variables involved, such as actual yield strength of base metals and weld metals, and variation of yield strength with temperature, this approach may not provide a practical solution.

Several other methods of minimizing this problem include:

Each of these options has resulted in a significant increase in the installed cost of the Coke Drum with limited success to date.

CB&I’s Solution

CB&I’s solution to this problem is an idea which would eliminate the circumferential seams altogether in the area of concern. Orienting the shell plates with their long direction vertical accomplishes this, providing an increased (up to more than 40 feet) shell length without a girth seam. This section of the vessel can be located in the areas that experience the most severe thermal cycles.

CB&I has developed this method and has applied for a patent for this solution to the bulging and cracking problem. This concept has been discussed with several individuals experienced and knowledgeable in Coke Drum design and operation and has received their endorsement.

Concept Development

Development of the concept has been completed. There are no design or Code issues. CB&I knew clad plates over 40′ long in the thickness ranges desired could be obtained. CB&I has the required manufacturing facilities and know-how to form these plates within the required tolerances. This has been confirmed by forming a test plate (40′ x 8′ x 1.5″) in CB&I’s Houston manufacturing facility. The results showed that the formed plate met the necessary tolerances to fabricate and erect the plates in this manner.

CB&I is prepared to provide Coke Drums built with this innovation. CB&I will:

Advantages:

There are two significant advantages in a Coke Drum built with this innovation

This innovation along with other Coke Drum innovations (i.e. such as skirt to shell attachment welds) will provide vessels with a longer operating life and lower repair costs.


 

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