B31 - steam/cond pipe wall thickness
B31 - steam/cond pipe wall thickness
(OP)
Probably a pretty simple question for you guys. A supplier designing and installing a low pressure (3barg) steam line for a refinery plant has specified schedule 10 pipe work. The extent of their design currently is that schedule 10 is pressure rated > 3barg, with no calcs in alignment with any code. The demand is as high as 1500kg/hr, and thus to obtain acceptable operating velocities the line size is DN100. We have had a number of issues with this supplier, namely poor understanding of local engineering standards in New Zealand where this project is being complete (they are Malasyia based where standards are typically lower I presume). This and a number of other issues causes me to question their capabilities in some errors. Effectively we follow AS4041, which mirrors ASME B31. I have instructed them to prepare design documentation in accordance with this for us to review, but prior to this I want to check something: Under this code, the pipe will certainly come under hazard class E. I have never though in my short career seen steam and condensate pipe work be installed in schedule 10, even at lower pressures. Alas, a code is a code, what is the industry standard out there and what might you recommend?





RE: B31 - steam/cond pipe wall thickness
Using schedule 10 carbon steel for corrosive condensate return service is asking for disaster.
Condensate return piping is subject to internal corrosion from carbonic acid, as well as many other abrasive and corrosive agents that can be picked up in refinery service. This piping can also undergo flashing and mechanical hammer loads
Schedule 80 piping is commonly specified for condensate return service, even though an ASME B31.1 code based wall thickness calculation indicates a thinner wall thickness is acceptable.
http://www.plantengineering.com/single-article/bes...
http://www.pharmpro.com/product-release/2005/06/ma...
Specifying a minimum of schedule 40 CS for the steam portion of this system is, IMHO, simply good practice.
MJCronin
Sr. Process Engineer
RE: B31 - steam/cond pipe wall thickness
Schedule 40 fittings can be threaded and socket welded. Socket welding of schedule 10 is somewhat possible, but difficult.
MJCronin
Sr. Process Engineer
RE: B31 - steam/cond pipe wall thickness
both f these have sections where it states that for mechanical strength you need to increase the wall thickness above the minimum required for pressure containment.
Thermal expansion stress is another issue seemingly not considered?
I agree at this size the usual minimum is schd 80. Savings in pipe costs are usually minimal compared to the total for the package, but a straightforward pressure containment calculation ( possibly with no corrosion allowance) will show sch 10 is good enough
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: B31 - steam/cond pipe wall thickness
RE: B31 - steam/cond pipe wall thickness
Stress simply needs to be analysed properly. There are no guides within the codes, only from custom and practice.
A lot of times you're better off with fewer anchors and more flexibility. All anchors do is lock in stresses a lot of times.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: B31 - steam/cond pipe wall thickness
The largest dairy factory in the Southern Hemisphere (Kiwi Dairy in Hawera) had Sch 10 S/S lines for Steam and Condensate over 30 years ago.
I was only a newbie then and was working on another part of the plant but I wondered how you could possibly hydrotest something with such a small wall thickness.
No idea if those lines are still in service.
Regards,
DD
RE: B31 - steam/cond pipe wall thickness
RE: B31 - steam/cond pipe wall thickness
And yes sch10 SS is common such lines.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: B31 - steam/cond pipe wall thickness
Can you tell me where the Carbonic acid comes from in a steam/condensate system? Never heard of Carbonic acid in a steam/condensate system in my 37 years in the game.
RE: B31 - steam/cond pipe wall thickness
RE: B31 - steam/cond pipe wall thickness
GE and several other sources discuss Carbonic Acid generation in Boiler water systems...
An excerpt from the GE Boiler Water Systems Handbook:
http://www.gewater.com/handbook/boiler_water_syste...
MJCronin
Sr. Process Engineer
RE: B31 - steam/cond pipe wall thickness
Ask the supplier to provide the piping design calculations and piping models so you can check they are working to local design requirements.
RE: B31 - steam/cond pipe wall thickness
I failed to read your OP properly.
AS 4041 does not mirror ASME B31 (B31.1 or B31.3)- they are hugely different.
They have taken a lot of material out of B31.1 and B31.3 but as codes they are not comparable.
Here is an excerpt from the Preface of AS 4041 that may be applicable to your question.
Comparison of this Standard with ASME B31.1, Power piping and ASME B31.3 shows that
for the same pressure and application, piping to this Standard may be thinner than piping to
the two American Standards at low to medium temperatures.
Regards,
DD
RE: B31 - steam/cond pipe wall thickness
ANSI/ASME B31.3, Process piping, and BS 806, Specification for the design and
construction of ferrous piping installations for and in connection with land boilers, as
well as Australian Standards. This has been done where practicable to align with
international practices to provide flexibility in design and to enable current proven
computer programs for either of the above Standards to be used to satisfy the design
requirements of this Standard (see Clause 1.6).
ANSI/ASME B31.5 are deemed to meet the requirements of this Standard (see
Clause 1.6).
1.6 ALTERNATIVE STANDARDS Piping complying with the following alternative
Standards is deemed to comply with this Standard, according to their particular scope,
provided that any requirement of this Standard nominated by the owner is complied with:
(a) Piping for power plant . . . . . . . . . . . . . . . . . . . BS 806 or ANSI/ASME B31.1.
(b) Piping for chemical plant . . . . . . . . . . . . . . . . . . . . . . . . . ANSI/ASME B31.3.
(c) Piping for refrigeration plant . . . . . . . . . . . . . . . . . . . . . . ANSI/ASME B31.5.
Mixing the content of application Standards is not permitted except where agreed by the
parties concerned. The materials, design, construction, testing and inspection of the
alternative specification shall be used in full unless otherwise agreed.