[MW:1826] Reason for RT shall be taken after 24 hours but within 48 hours?

Dear all,

Could anyone please advise, why shell standards are stipulating the
following as supplements for "WELDING OF PIPELINES AND RELATED
FACILITIES-(CLASS-1)", as

"If cellulose electrodes are used, radiographs shall be taken after 24
hours but within 48 hours of weld completion. If a low hydrogen
process is used, radiographs may be taken within 24 hours of weld
completion."

Generally, if other than low hydrogen electrodes are used for
production welding (like cellulose), possibility of hydrogen
entrapment could occur in the WM/HAZ and as a result Delayed/Cold
Cracking could occur after 72 hours. If this is the case, then
radiography should be taken after 72 hours, BUT WHY shell standards
are insisting to take RT after 24 hours, but before 48 hours. If
incase cracking happened after 72 hours means, then how it can be
identified-prior to hydro testing.

Also, whats the reason behind to take RT within 24 hours of weld
completion, if LOW HYD.Electrodes/process utilized.

Please advise.

Thanks,

Ari

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