piping

In addition - according to ASME B31.3 - the bevel must be no greater than 30 deg. taken from the pipe wall. That is, it must be a fairly shallow bevel from the root.

hello,

I have one doubt that in ASME B16.25,for welding of thickness over 3mm to 22mm,it has given two things.First,it says slope of 1:3 is maximum has to given and Second it also says to have 30 degree angle(maximum) between root and inside diameter.So,when and which one i have to follow.They also have mention to give 15MM minimum distance from root,so this distance is for backing ring? and if i am not putting any backing ring and still i am giving this distance ,is there will be any problem?Kindly can you explain in detail.

Thanks

Dear Lahane82,

Per ASME Code, the max. slope shall be 1:3 (that means you can use slopes 1:4, 1:5, ... etc.), and this taper is measured from the center of the groove weld. That means that the ASME code accepts that the weld bead can be located at the portion of tapering. For me, I prefer (and I do that in all my designs) that the taper to be measured from the end point of the groove weld angle (toe) to avoid the "high-low" markings through the image of x-ray film. Otherwise the unexperienced inspectors will say that there is a "high-low" defect in the weld.

Thanks for reply,

So i can go for taper with slope as you have mentioned above with backing ring also?.In B16.25 it has mentioned some 15MM minimum distance ,is that for backing ring placement or for something else and after that it has mentioned taper with maximum 30 degree angle upto inside surface of pipe.Can you explain me what is purpose of this arrangement when we can use procedure as you have mentioned above.If possible kindly can you give me any clarification document if you do not mind it on my mail id nandkumarashok.lahane@siemens.com

Thanks for giving your precious time to me.

Thanks

Nandkumar

Thanks for reply,

So I can go for taper with slope as you have mentioned above with backing ring also?.In B16.25 it has mentioned some 15MM minimum distance, Is this for backing ring placement or something else and after that it has also mentioned taper with maximum 30 degree angle upto inside surface of pipe.Can you explain me what is purpose of this arrangement. If possible kindly can you provide some documents regarding this topic.

Thanks for giving your precious time to me.

Thanks

The solution is very simple as I explained:

1. Use taper from inside of thicker pipe with a max. slope of 1:3 (18.5^o).

2. Using a backing ring is an optional depending on the WPS's & PQR's.

3. The slope 1:3 makes an angle about 18.5^o. And ASME code recommend to use that max. slope because it will makes a gradually sloping between the two differ thicknesses which is recommended to facilitate transmission of stresses without local stress concentration at that portion.

4. Using an angle of 30^o will create a slope of 1:1.73, which is greater than 1:3, and that is not recommended, where the max. slope must be not more than 1:3.

Thanks for your reply,

What is purpose of mentioning of 30 degree maximum angle in ASME B16.25 (Kindly,See Figure.1 Maximum Envelope for Welding End Transition in ASME B16.25),if with slope of 1:3 ,angle is coming 18.5 degree maximum as you have mentioned above.Then ASME B 16.25 suppose to mention this angle not 30 degree.

Thanks

The term "max. envelope 30^o" doesn't means that this angle is the only one accepted, it means that there are a lot of envelopes smaller than 30^o are acceptable. So you can select any slope with a max. of 30^o angle.

Important note: angle 30^o is the max. angle with slope 1:1.73 (which stated by ASME B16.25), where 18.5^o is also accepted angle with slope 1:3 (which recommended by ASME VIII), and angle 14^o with slope 1:4 is also accepted, where angle 45^o is not accepted by both codes.

Dear Galala,

Thanks for your reply earlier. As we know for seamless and welded pipe we are taking +/-12.5% mill tolerance addition to minimum pipe wall thickness.We know ERW Pipe is rolled from plate,in this case vendor is taking or not plate tolerance as 0.01 inch or 6% of plate thickness ordered ,whichever is smaller(as per ASME)in addition to mill tolerance for that pipe while manufacturing .If answer is yes then why?and if vendor is not taking it then why not?

Thanks

A. For Pressure vessels in accordance with ASME code, Section VIII, the mill undertolerances are:

1. Plate Thickness Undertolerance, per UG-16(c) :

Plate material shall be ordered with thickness ≥ design thickness, and vessels made of plate shall be furnished with an undertolerance ≤ 0.01" (0.25 mm) or 6% T whichever is less. (where, T = The ordered thickness of plate).

Note : If the specification to which the plate is ordered allows a greater under tolerance, the ordered thickness of the materials shall be sufficiently greater than the design thickness, so that the thickness of the material furnished is not more than the smaller of 0.01" (0.25 mm) or 6% under the design thickness. And the term vessel here means the whole vessel and/or any pressure part like as shell course, formed head, nozzle fabricated from a plate, where the prescribed tolerance shall be applied.

2. Pipe Wall Thickness Undertolerance, UG-16(d), ASME/ANSI B36.10M & ASME BPVC Section II, Part A, SA106-Para. X2, Min. Wall Thickness, Table X-2:

After the minimum wall thickness is determined for pipe or tube, it shall be increased by an amount sufficient to provide the manufacturing undertolerance allowed in the pipe or tube specification (tn = tm / 0.875, i.e. Tolerance shall be : ± 12.5% t)

Note : An exception of that tolerance is for nozzle wall reinforcement area requirements for compensation in accordance with UG-37 and UG-40.

(where, tn = The ordered nominal average wall thickness of pipe or tube & tm = min. wall thickness).

B. For Pressure Piping in accordance with ASME Section II, Part A, the mill undertolerance is ± 12.5% t which indicates that tn = tm / 0.875, and applied for pipes or tubes for both seamless and seamwelded (fabricated from plates or sheets) as clear from ASME SA53 & SA 106.

Conclusion:

For BVPC, Section VIII, the undertolerance shall be:

• 0.01" (0.25 mm) for plates, and cylindrical shells or heads fabricated from plate or sheet.

• ± 12.5% t for pipes or tubes seamless or seamwelded which produced under name of pipe and/or tube (see exception as per UG-37 and UG-40).

For B31, Pressure Piping, the undertolerance shall be ± 12.5% t for both pipes or tubes seamless or seamwelded.

Dear Galala,

Can you explain me what is difference between hot load design Variable spring hanger and cold load design variable spring hanger if we see this in installment(Erection)point of view.What is erection procedure difference for this two design.Kindly,reply.

Thanks,

Nandkumar

Dear Lahane82,

"hot load design Variable spring hanger": this means the load inserted on that hanger while the hanger in service (in operation).

"cold load design variable spring hanger": this means the load inserted on that hanger while the hanger out of service (or during installation/erection).

Dear Galala,

Reducer of 10"X6" size ,but schedule of 10" pipe different than schedule of 6" pipe,then reducer(available in market) ends thickness will be different i.e maching with pipe schedule or it will be of thickness of higher/lower schedule.If available reducer thickness is of higher scedule thickness ,then are you do end preparation of reducer as per B.16.25 at the connection of lower schedule pipe.

Thanks,

Nandkumar

Hi Galala,

I hope you are well,

First of all I appreciate your great effort about helping us.

I have a question about "mill under tolerance".

Do I have to consider %12,5-mill under tolerance when making calculations according to ASME Piping Code B.31.8?

Because in B31.8 Paragrapgh 804.222, it says "Under this code, pipe may be ordered to this computed wall thickness without adding allowance to compensate for underthickness tolerance permitted in approved specifications"

So could I ignore to consider "Mill Undertolerance" in my calculations?

Regards

Cemal Tardu

Yes, that is true, because the equation for calculating the thickness for gas pipelines per ASME B31.8 is differ than the similar equations which used in B31.1, B31.3 and B31.4, where in B31.8: t = PD/(2 SFET) and many factors of safety already included at S, F & T.

And therefore it is an option for the designer to consider that tolerance or not (see the statement itself of para. 804.222: Under this code, pipe may be ordered to this computed wall thickness without adding allowance to compensate for the underthickness tolerance permitted in approved specifications), so it is the decision of the designer and/or owner with a contractual agreement with the installer to define that under tolerance in the contract.

In para. 804.222 I noted that no clear definition for that mill tolerance, and is it considered one of those "underthickness tolerance permitted in approved specifications" or not. Whatever, for me as a designer, I prefer to add any under tolerance in any design calculations.

Dear Mr.Galala,

In ASME B31.1,under fabrication and erection chapter it had shown that if internal mis-alignment of pipe is more 2 mm then ,pipe has trimmed inside.

My doubt is that, internal mis-alignment can be taken same as inside thickness difference of pipe.

or

Internal mis-alignment and inside thickness difference of pipe both are different concept.

I don't believe I have ever heard anyone explain this better than Abdel Halim Galala. I was gonna take a stab at it but it has already been said. Thanks for having the experiance and the patiance to stay with it and get it all said. You get my GA.

pipewelder

My dear pipewelder,

Thank you very much.

Dear Sir,

Reducer of 10"X6" size ,but schedule of 10" pipe different than schedule of 6" pipe,then reducer(available in market) ends thickness will be different i.e maching with pipe schedule or it will be of thickness of higher/lower schedule.If available reducer thickness is of higher scedule thickness ,then are you do end preparation of reducer as per B.16.25 at the connection of lower schedule pipe.

Thanks,

Nandkumar

Hi,

Reducers have mostly two different end thicknesses. (ASME B.16.9 - 1993)

For example reducer 10"x6" Sch XS ------>

Small side has 10,97mm

and

Large side has 12,70mm

When using reducers in pig launcher and receivers, as you know we put it between

minor and major barrels, and many times reducer thicknesses' may be differ from pipe thicknesses which they attached. And at this time we have to make taper inside pipes for smooth transition.

But in pigging process, we must to provide very smooth transition between pipes and reducers avoid stucking pig device.

Minimum taper height, Maximum smootness transition!

There are transition tolerance values for pigging units.

Dear Sir,

In B16.9 ,where it has mentioned about reducer having two diff.thickness.(I am thinking it might be having same thickness throughout the reducer available in market as large pipe schedule thickness)

One more doubt I would like to ask that Pipe comes with end preparation from factory,so to make end preparation again do you cut the end of pipe or Is there any other arrangement?

Regards,

Nandkumar

Hi,

If you make a end preperation, it will be obviıusly better for the strength.

You can also follow the well-known end preparation methods for flanges.

According to ASME B.16.25;

1- Up to 22mm

1,6mm height and 37,5 degree weld angle from one side.

2- Above 22mm

First 1,6mm vertical height and 17,4mm with 37,5 degree welding angle.

Then provide 10 degree angle till material surface.

Cheers

Cemal