Hot Tapping of Vessel 1

[ProjEngr]

I would like to hot tap a few 1" connections on an existing tower to install some differential pressure transmitters. To install these hot taps, we would use a Sockolet with a nipple and a valve. My inspection department will not let me do these taps, even though ASME VIII allows it. The tower is made of SA212B material. Inspection is worried about laminations in the metal from the bending process. According to inspection, if a hot tap would take place in a lamination zone, the vessel wall metal thickness could be compromised when the process got into this lamination and started to corrode it. Has anyone else ever heard of this type of failure? Are there ways to externally find these laminations? The vessel is a Debutanizer. The taps are located mid-tower and at the top of the tower.

 

[MJCronin]

proj,

I suggest that you investigate the properties of the SA212 Grade B shell and of the SA212 ASME material specification.

I also suggest that you consider an ultrasonic inspection of the desired area. (Typically, not too expensive)
This should be able to detect laminations in the vessel shell.

Laminations can occur only with steels that are not "fully killed" (all disolved gasses are removed from the ingot by both chemical and mechanical means). "Fully killed" steels were developed many years ago to address the problem of laminations.

While laminations can occur in thick sections of A36 steel,(a structural steel) they are rarely found in in SA516-GR70 (a commonly used pressure vessel grade of steel)

Please let us know what you decide and your reasons .....

Consider posting this question on the "Bolier and Pressure Vessel Engineering Forum

MJC

 

[Rich2001]

>Are there ways to externally find these laminations?
UT ( Ultrasonic ) testing is routinely done to locate laminiations.

 

[athomas236]

I assume that we are talking about laminations that have occured during the bending process of manufacture, what you have to ask yourself is how did these bent plates ever get approval to enter service. Sounds let your inspection dept are more concerned with CYA than doing the job. I would do ultrasonics on the plates and drill the hot taps. If you really want to be sure just buy some replacement plate already rolled and certified to weld in just in case.