refer old postings on the group, we have lot of dicussion in the past
on this subject.
refer code case 181
"ASME B31 committee has developed B31 Case 181 to permit the use of
UT, particularly TOFD in lieu of RT for B31.3 applications. ASME B31
case 181 was apparently taken from ASME Code Case 2235, which
addresses the UT examination in lieu of RT for vessels and not piping.
The major difference from what I can see between B31 case 181 and ASME
Code Case 2235 is the minimum wall thickness requirements and maybe
the acceptance criteria.
As we all know ASME B&PV codes looks at flaws by aspect ratios. a/l or
vertical height divided by length. That gives you the aspect ratio
which is then used to determine the maximum flaw size permitted. You
can actually accept cracks per the ASME B&PV code as long as they are
within the acceptable limits, but not with ASME B31.3.
After looking at the acceptance criteria for B31 Case 181, I see that
they are using the same philosophy.
Where ASME B31.3, Table 341.3.2 does not allow any cracks for RT and
in most cases no IF. Why would cracks be permitted with UT and not RT?
I believe the B31 Case 181 was taken from ASME Code Case 2235 and the
reference to cracks was inadvertently missed. When using TOFD you can
differentiate between linear indications and cracks. Does anyone know
of any reference by ASME B31 committee regarding this issue?"
Source: ndt.net
On May 28, 6:37 am, tong tong <tong...@gmail.com> wrote:
> Dear All members,
> I really need you expertise opinion on the above mentioned subject.
> Basically our project(new piping installation) requirement is RT but we
> having a lot of problems to do it. One of the major problem is the window
> which is very limited. To avoid any backlog i purpose to my boss to go for
> UT instead of RT. It is permissible by the code and standards to do UT
> instead of RT. Which code and standard we should refer?. Thank in advance
> for your kind cooperation
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