Chemical Engineering August 2021 - 41

P = (2 × 0.107 × 20,000)/1.315
= 3,254 psig
= Theoretical burst pressure
By then applying a safety, Sf, of
4, as recommended in the ASME
Pressure Vessel Code Section VIII-1
2019, para. UG-101, the calculation
would look like the following:
Pa = 3,254/4 = 813.5 psig, or say
810 psig MAWP
The resulting 810 psig MAWP
applies to the pipe only. The flange
joints, or the lowest rated component
in the system will be the governing
factor in determining the allowable
pressure for the system.
Based on ASME B16.5, at temperatures
from -20°F to 100°F, the
Class 150 carbon-steel flange joint
has a maximum allowable working
pressure of 285 psig. Class 300 has
a maximum allowable working pressure
of 740 psig. This will be the
limiting pressure-containing factor
for the system as per the following
material specification example. And
additionally, those values can be exceeded
by a factor of 1.5 for hydrotesting
only.
Example specification
As an example for a basic carbonsteel
material specification, a pipe
specification for gaseous H2 service
operating at ambient temperatures
with design pressures below
740 psig might consist of the material
requirements shown in Table
3. The following are the types of
notes that might be included in the
specification:
1. Examination shall include 100%
radiography or ultrasonic examination
of all welds.
2. Installation should minimize
or eliminate the use of breakout
flanges. Flange joints should only
exist at flanged equipment, including
instruments, and flanged valves.
3. When a carbon-steel-to-carbon
steel
threaded connection
is
required,
do not apply thread compound
during assembly.
Seal-weld
after full thread engagement.
4. Examine 100% of buttwelds by
non-destructive testing (NDT) methods,
such as radiography or ultrasonic,
prior to PWHT. Document the
examination process.
5. Welds shall be post weld heat
treated. PWHT is required to prevent
HTHA of the pipe weld seam and
material around the heat affected
zone at weld joints. The service provider
shall provide documentation
of the PWHT process. As an alternative,
weld metal hardness controls
can be put in place such that
the maximum weld metal hardness
in carbon steel is equal to or less
than 200BHN and weld procedure
qualification testing shall be done
to ensure that the hardness of the
heat-affected zone (HAZ) at each
weld does not exceed 248 VHN (reference:
NACE RP0472).
6. The maximum design limit is
based on the weakest component in
the system. It is not based strictly on
the maximum temperature or maximum
pressure of the component,
but on the highest allowable coincident
of the two.
Honorable mention
There are many elements, other
than the pipe itself, that make up
a piping system, such as fittings,
valves, inline equipment, and so
on. And while many of these items
would be incorporated to make up
a piping system to discuss them at
length would require more pages
than this article can accommodate.
Having said that, the same information
found in this article can also
be applied to the fittings, valves
and inline equipment that make up
a gaseous hydrogen piping system.
Leak testing
When installing a piping system for a
material as potentially volatile as H2 a
procedure for leak testing should be
established that not only sets forth
thorough and definitive guidelines,
but also identifies the best suitable
means of assuring system integrity.
Part of that assurance lies with the
leak testing procedure. Using a twoLooking
for that dream
job in the chemical
process industries?
Post your resume and cover letter at chemengonline.com/chemploy today!
» Chemploy job center focuses exclusively on jobs in the CPI
» Receive job alerts directly to your email of any new jobs
posted that match your search preferences
» Access the Careers Resources library which offers you
valuable coaching and career guides
If interested in posting a job, please contact:
TERRY DAVIS
404-634-5123 | tdavis@accessintel.com
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
AUGUST 2021
JASON BULLOCK
713-974-0911| jbullock@chemengonline.com
31701
39
Create an account
now and never miss
a new opportunity!
Don't let the competition
score that perfect
position you deserve.
http://www.chemengonline.com/chemploy http://WWW.CHEMENGONLINE.COM
Chemical Engineering August 2021

Table of Contents for the Digital Edition of Chemical Engineering August 2021
