Hydrotest+30F from API 510

[kevlar49]

If the shell is to be hydrotested, the tube sheet of an exchanger is 4 inches thick but the shell is 1 inch thick would you add 30 F to the hydrotest temperature in accordance with api 510 2003 ed. para. 6.5 that states the hydrotest should be conducted at 30F over the MDMT if the section is >2 inches thick?

 

[gr2vessels]

Clause 5.8.6.2 of API 510 - 2006 says "To minimize the risk of brittle fracture during a pressure test, the metal temperature should be maintained at least 30ºF (17ºC) above the MDMT for vessels that are more than 2 in. (5 cm) thick, and 10ºF (6ºC) above the MDMT for vessels that have a thickness of 2 in. (5 cm) or less. The test temperature need not exceed 120ºF (50ºC) unless there is information on the brittle characteristics of the vessel material indicating a higher test temperature is needed".

My experience is that the thicker is C/S the material, the more risk of low temp brittle fracture.

There is no description of the 2" reference, as to the shell thickness, flange thickness or tubesheet thickness. However, I would have thought that the thick tubesheet bolted or welded to the shell is part of the hydrotest, isn't it? Then the condition of 30ºF (17ºC)above the MDMT I believe applies to the tubesheet also.
Cheers,
gr2vessels