B31.1 or B31.3 for steam lines? 5

[garfio]

The piping for a chemical plant has to comply with ANSI B31.3, but what specifically applies to the steam
lines?

ANSI B31.3 mentions that it also applies to steam and excludes "boiler external piping" (no mention to non-boiler external piping).

But if you go to ANSI B31.1, is says that it applies to "piping typically found in ... industrial and institutional plants..." (a chemical plant would be included there), and also mentioned that "non-boiler
external piping" shall comply with ANSI B31 codes.

Nayyar's book 7th edition, shows an jurisdictional limits drawing taken from an old B31.3, which shows lines
coming from a power boiler, as covered by B31.3 but with a note: "optional for B31.1".

1) What do you think should be used for steam in a chemical plant? What do you use?

2) Which code would be more conservative in this particular service (150 to 450 psi saturated steam) in regards

to stresses?


Thanks

 

[NozzleTwister]

In a chemical plant, almost all of your steam piping will be per ASME B31.3.

Go to those figures shown in Section 100 at the beginning of ASME B31.1. The sold lines are Boiler External piping and are per B31.1. The Dotted lines are nonboiler external piping and will be per another piping code. For chemical plants and refineries and most other process facilities, this will be ASME B31.3. (In the U.S. anyway and many other parts of the world)

You may find the following useful.

quote from B31.1, section 100.1.2
Boiler external piping shall be considered as that piping
which begins where the boiler proper terminates at
(A) the first circumferential joint for welding end
connections; or
(B) the face of the first flange in bolted flanged
connections; or
(C) the first threaded joint in that type of connection;
and which extends up to and including the valve
or valves required by para. 122.1.
The terminal points themselves are considered part
of the boiler external piping. The terminal points and
piping external to power boilers are illustrated by Figs.
100.1.2(A), 100.1.2(B), and 100.1.2(C).

Many times Code breaks are shown on the P&ID's.

I hope this helps.


NozzleTwister
Houston, Texas

 

[RossABQ]

I don't think it's fair to say B31.1 or B31.3 is more conservative than the other; compare the QA requirements (hydro, radiography, etc) and you'll see they accomplish more or less the same thing but in different ways.

 

[JohnBreen]

Hi garfio,

First and foremost - it is the RESPONSIBILITY of the facility owner to specify what Code he wants to apply to the piping systems. The specification of the required Code should be a part of the owner's original Request for Proposal, so that all those offering a bid (tender) would understand the scope that they are bidding on.

If the consultant to the owner is to assist the owner in deciding and specifying the applicable piping Code it would be common practice for the consultant to advise the owner to specify that all the piping on the petroleum refinery or chemical plant or food processing plant or research facility or................. (excluding power generating facilities and excluding district heating plants) be designed, fabricated, erected, examined and tested in compliance with the ASME B31 Code for Pressure Piping, B31.3, Process Piping.

Having said that, many owners will specify that all on-site (within the process units battery limits) piping and all off-site piping in the refinery, with exception, be constructed in compliance with the B31.3 Code. The exception that is occasionally made is at central boiler plants or central power plants within the facility boundaries. For these central plants (within the boiler/power unit boundary limits) the owner might want all the piping IN THE STEAM/WATER CIRCUIT, again - within the boiler/power unit boundary limits, to be constructed in accordance with the B31.1 Code. In this case the steam/water circuit outside the boiler/power unit boundary limits would revert to construction in accordance with the B31.3 Code. Regardless, all boiler external piping, as defined by ASME B&PV Code, Section 1, and as defined by B31.1, would be ADMINISTRATIVELY Section 1 but for detailed design purposes would be constructed in accordance with B31.1.

Regarding the perceived relative conservatism of the various ASME B31 Codes for Pressure Piping: this is a individual engineer's perception based upon each Code's maximum allowable stress for materials of construction at temperature (see B31.1 Appendix A and B31.3 Appendix A). For a long time, the allowable stresses found in B31.1 were based upon a factor of safety of 4 and the allowable stresses found in B31.3 were based upon a factor of safety of 3. If one will pay attention to the ASME B&PV Code and ASME B31 Codes for Pressure Piping one would see that there have been changes and there will be more changes. Stay tuned!

Regards, John.

 

[garfio]

Thanks for all the input. If I understand correctly, normally it is used B31.3 for all the piping system in a chemical plant, unless is has a power boiler (meaning for the purpose of generation power, not for regular plant consumption), unless different requirement from the owner.

Regarding what RossABQ said, I agree that each B31 section should be interpreted as a unit, but I was trying to get a feeling of the stress requirements. After some more digging, I found what JohnBreen mentioned regarding B31.1 using lower allowable stresses and that they were studying some changes. I also found that besides the allowable stresses, there are some other elements that makes B31.1 more strict (in terms of stresses), like the use of a single SIF, equal to the highest of the two in B31.3.

 

[unclesyd]

Adding a little to JohnBreen's post.
All our steam distribution system of any pressure throughout the site is designed and fabricated to ASME 31.1 and totally under operational and administrative control of the powerhouse up to the block valves at the battery limits of each building. If the building uses high pressure steam (650 psig @ 750F) the piping is still designed and fabricated to ASME 31.1 though it's controlled by the local area from the block valve. Any steam piping beyond the block valves at lower pressure is designed and fabricated to ASME 31.3 and again administered by the local area.

One thing that this system does is that it ensures coordination of any operational or mechanical changes to the steam distribution system is controlled by the powerhouse.

 

[GregLamberson]

JohnBreen is correct,m it is up to the owner to specify B31.1 or B31.3. My experience has been B31.3 is the more common choice.

But one thing that is often missing in the decision is the overall impact it will have on the facility - engineering, procurement, fabrication & installation, and operations.

I do allot of work in constructability. Yes, the codes will differ in wall thicknesses, material selection & stress calcs, but it will also have an impact on fabrication & installation, inspection & NDT, CP considerations, and O&M. Granted some of the distinctions are minor, but in a large facility should not be taken lightly.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com