TUBES BOWING ACCEPTANCE CRITERIA IN FIRED HEATERS-API RP573 1

[sappy]

1. Please describe the difference between Bowing and Sagging of tubes in Fired heaters and do the same acceptance limits apply for Bowed as well as sagged tubes.
In both sagging and bowing, tubes deformation is due to creep phenomenon as per API RP 573. So the acceptance limit of both sagged or bowed tubes should be same.

As per API RP 573 Edition 2003, TABLE 3 Acceptance limits for tube Deterioration Mechanisms, the acceptance limit for Sagged Tubes is given as 5 * Tube diameter.
Whereas according to ABSA code AB-507 (Edition: 1999, Revision 02) PAGE NO. 8, Tube Bowing acceptance limit is given as 1* Tube diameter.

2. Acceptance limit of Bowing is required in case of vertical tubes of heaters with reference to applicable code and standard.

 

[chicopee]

Normally tube sagging in horizontal fire tube boilers will happen when low water condition takes place upon which time cold water is introduced into the boiler and setting the tube in permanent deformation. When sagging occurs, there is a good chance that you'll have tube to tube contact upsetting the natural circulation of water around the tubes. I am not familiar with what would cause the tube to bow.

 

[EdStainless]

Bowing is not creep. People use the term bowing to describe when tubes are unevenly heated or excessively constrained when heated. In these cases the tubes will bow as they try to expand.
This usually indicates a mechanical problem.

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P.E. Metallurgy, Plymouth Tube

 

[sappy]

Thanks for your replies. Furthermore, Acceptance limit of Bowing is required in case of vertical tubes of heaters.

As per API RP 573 Edition 2003, TABLE 3 Acceptance limits for tube Deterioration Mechanisms, the acceptance limit for Sagged Tubes is given as 5 * Tube diameter.
As per API RP 573, Both tube sagging and bowing phenomenon are due to CREEP (YIELDING). Is the Acceptance limit same for Bowed OR Sagged tubes ?
Whereas according to ABSA code AB-507 (Edition: 1999, Revision 02) PAGE NO. 8, Tube Bowing acceptance limit is given as 1* Tube diameter.

 

[metengr]

You have your answer above.