B31 - steam/cond pipe wall thickness 2

[jph90]

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?

 

[MJCronin]

You have not mentioned the materials of construction.... But lets assume carbon steel.

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/sin...-piping/787db15e4e6be928f01d59744cc6564c.html

http://www.pharmpro.com/product-rel...am-piping-safe10-simple-rules-and-things-look

Specifying a minimum of schedule 40 CS for the steam portion of this system is, IMHO, simply good practice.

MJCronin
Sr. Process Engineer

 

[MJCronin]

Its also important to also note that schedule 10 piping CANNOT be threaded because of it's thin wall.

Schedule 40 fittings can be threaded and socket welded. Socket welding of schedule 10 is somewhat possible, but difficult.





MJCronin
Sr. Process Engineer

 

[LittleInch]

ASME B 31 covers many codes, though I assume you mean either 31.1 or 31.3.

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.

 

[jph90]

Apologies should have stated - yes B31.3 and material specification is SS316 (stainless steel). As for thermal expansion stress, the pipe run is short and only 40-50 m long on the process side (Following PRV). to reduce impact of thermal stresses I assume it comes down to ensuring adequate anchor points on the pipe supports? Typically the lines will be on brackets permitting axial movement, with various anchor points allocated. Is there a good guide to follow on selection of anchor points? Is this covered in Any of the B31 sub codes?

 

[LittleInch]

That makes a big difference - schd 10S is fairly common.

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.

 

[DekDee]

jph90,
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

 

[racookpe1978]

A break in a low pressure cold milk plant near people (and cows) is not really comparable with a crack in a hot steam pipe above people.

 

[EdStainless]

Sch10 SS needs to be supported, but don't constrain it. Allowing for some distortion from thermal expansion is much better than having high stresses in the line (or support).
And yes sch10 SS is common such lines.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[DSB123]

MJCronin,
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.

 

[metengr]

http://www.chemtreat.com/capabilities/boiler-treatment/steam-and-condensate/

 

[MJCronin]

DSB,

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_systems/ch_19_Condensate.jsp

MJCronin
Sr. Process Engineer

 

[KevinNZ]

Note, NZ piping also needs earthquake design as well as the usual thermal and sustained load checks. A piping designer in Malaysia should be using B31.3 or B31.1 but they maybe completely unaware of the seismic design loads. The same applies to the support design. IPENZ PN19 provides guidance on seismic design requirements.

Ask the supplier to provide the piping design calculations and piping models so you can check they are working to local design requirements.

 

[DekDee]

jph90,
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

 

[KevinNZ]

DekDee also note the paragraph above the one you quoted. Piping designed to B331.1 or B31.3 passes AS4041.

This Standard makes use of current American and British Standards such as
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).

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also

Piping complying with BS 806, ANSI/ASME B31.1, ANSI/ASME B31.3 and
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.
​