Level DP on a Pad Flange Connection

Well, that is why the vessel is subject to pressure testing and insurance certification upon construction and at intervals determined by the company responsible for providing burst indemnity insurance cover for the facility.

Obviously, should one pressurise the vessel beyond its test point one is asking for a whole heap of trouble.

Leaking? Drain the vessel, change the joint and torque-up the bolts to the correct tightness; no insurance re-test required. Woss the problem <rhetorical question>?

1. Is your Chemical plant an existing plant or a new plant under erection? 2. Do you have all the specs. of the pharma plant, about which you read in a previous post? 3. What is the basis of your comparison? 4. Who did design the use of a pad flange connection for Level DP on most tanks and exchangers? Was it you?

Your answers to above will help.

ASME/ANSI B16.5 define the flanges and bolt dimensions for Classes 150 to 2500

The dimensions show that the 'pad' is a conventional 3", Class 150 flange:

The flange diameter is 190mm, nominally 7.5"
The distance between the bolt holes in the flange is 152.5mm, nominally 6.0 inches.
The flange face diameter is 127mm, nominally 5 inches.
There are 4 bolts (4 x 5/8-11 UNC).

The temperature and pressure ratings of the 150# flanges are well documented. Are you disputing whether a 150# flange is not adequate for operational temperature and pressure conditions?

3" flanges are widely used for instrumentation access ports in the USA.

As the instrument engineer, I'd say your responsibility would be that the transmitter would physically bolt-up to the pad flange provided. If, as someone noted, this is equivalent to 150# class, is your transmitter 150#? Many instruments I've dealt with aren't available below 300# class. Also, double check that the pad is physically located where your instrument will measure the desired level range. And check, or provide dimensions to the layout designers, that physical installation does not interfere with anything else.