Please, I´d need to know the applicable standard for UT on A240 Tp 316L, 3/4" thick plates. I see that ASTM A578 is for rolled carbon and alloy steel plates.
Just remember that you need two things if you are calling out this test, a test method (usually an E spec) and an acceptance criteria (usually found in a general requirements or product spec). Without both you don't have a real test.
Some companies have internal specs which call for UT of stainless for specific reasons/applications. The internal spec provides method and acceptance criteria.
Why write ones when they already exist? Use references that someone else in maintaining for you.
With testing of plate the issue of extent of coverage is usually one that gets overlooked.
SA-435
1.1 This specification covers the procedure and acceptance
standards for straight-beam, pulse-echo, ultrasonic examination
of rolled fully killed carbon and alloy steel plates, 1⁄2 in.
[12.5 mm] and over in thickness. It was developed to ASSURE
DELIVERY of steel plates free of gross internal discontinuities
such as pipe, ruptures, or laminations and is to be used
whenever the inquiry, contract, order, or specification states
that the plates are to be subjected to ultrasonic examination.
During fabrication of pressure vessel you can use SA-577 or SA. 578. UT is used before and after cutting a hole for a nozzle