RE: [PipingDesign] Thread engagement? - Bolt Strength and NACE

From: <Sajit>
Date: Tue Jul 19 2005 - 03:34:00 EDT

"(to the effect that most or all bolting load is normally carried by the first few threads nearest the bearing face,"

This probably must be the reason that ASME B16.5 does not include the free threads in calculating the stud length.

In this context, I have a related question,

Fastners subjected to SOUR service (not exposed bolts) requires bolts to be heat treated to bring the hardness values within the limits of NACE MR 0175. However such bolts are of the intermediate to low strength. The use of these bolts are restricted by B16.5.

It says that, "These bolting materials may be used with all listed materials and gaskets, provided it has been verified that a sealed
joint can be maintained under rated working pressure and temperature."

Many piping classes use the B7M, B8M bolts.

It appears that a flange calcualtion is to be done to verify the gasket seating with the lower strength bolts. If the bolt load turns out to be less (at the allowable stress stated by ASME B31.3 Table A1) than required by the gasket seating and at the flange rating pressure. The bolt size cannot be increased.

Has anyone done, perhaps a representative calculation for say a 12" 2500# with a B8M bolt, to ensure this.

Sajit


You have not stated the specific application, any other specifications, whether regular or heavy hex nuts are involved, nor service etc., but I believe some steel flange specifications do have information that might at least relate to this issue. For example, AWWA C207 talking about steel pipe flanges for waterworks service provides tolerances for many components such as flange thicknesses, states on page 5 that the minimum bolt lengths shall basically be the sum of the maximum thicknesses of mating flange thicknesses, plus the gasket, plus the nut plus 1/8 in., and on pg 6, "If threaded rods are used, they shall be the same length as the bolts determined previously, plus the depth of the nuts, plus 1/8 in. (3.2 mm)."

That being said (and perhaps checked per your specs etc.?) I do suspect the engagement as described will develop substantial bolting strength, as I think I've seen many years ago incomplete thread engagement issues discussed in some technical articles on design of threaded fasteners (to the effect that most or all bolting load is normally carried by the first few threads nearest the bearing face, and of course the bolts and threads have apparently successfully taken whatever torque load the installer has put on them so far!) -- I guess whether that is adequate for your long term service might depend on the service requirements, the actual bolting material properties, or other factors etc. I hope this information is of help.

Randy Conner

-----Original Message-----
From: PipingDesign@yahoogroups.com
[mailto:PipingDesign@yahoogroups.com]On Behalf Of
Davis McConnico
Sent: Friday, July 15, 2005 9:37 AM
To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] Thread engagement?

sorry, replied to Paul as a posted question, should have had a pertinent "subject".

-Davis

   Sent: Friday, July 15, 2005 9:28 AM
   Subject: Re: [PipingDesign] New Current Interesting Links

   Does anyone know of any codes pertinent in the USA which address the engagement of bolt/stud with the nut on ASME B16.5 Class 150 and 300 flanges? I have a customer that recently installed some gaskets in a shutdown. The studs were a bit short and the nuts lacked about a half thread on each end before full engagement. I've asked around and read some literature and found only suggestions stressing the importance ranging from full engagement to having at least two threads showing beyond each nut. But I can't find any relevant codes. Re-installing these gaskets with longer studs would require plant shutdown again.

   Thanks all,

   -Davis

     To:
PipingDesign@yahoogroups.com<mailto:PipingDesign@yahoogroups.com<mailto:PipingDe\ sign@yahoogroups.com<mailto:PipingDesign@yahoogroups.com>>

     Sent: Wednesday, July 13, 2005 9:44 PM
     Subject: [PipingDesign] New Current Interesting
Links

     Linked from the current version of the main page, www.pipingdesign.com<http://www.pipingdesign.com/<http://www.pipingdesigncom<htt\ p://www.pipingdesign.com/>>:

     The Art of Checking Pipe Stress Computer Programs
[PDF]
     Treatment of Support Friction in Pipe Stress Analysis [PDF]

     The Art of Designing Piping Support Systems [PDF]


     An excerpt from one of the above links is quoted below:

     "Pipe stress analysts are normally too timid in challenging a well

     established computer program. However, if we recognize that to err is

     computer program, we may be able to more objectively ensure the quality

     of our analysis. It is important to realize that everything has its so

     called norm. In other words, if something looks unrealistic then it

     probably is unreal. Therefore, it is important to be able to look at the

     output and point out the irregularities that might exist. That is the

     art. From time to time we have seen some experienced engineers who are

     able to judge whether a system is satisfactory just by looking at the

     model. The computer analysis is just confirming a check. However, they

     are the exceptional rather than the normal.

     The inconsistent results in an analysis comes either from the bug in the

     program or from the misapplication of the program. Nowadays, people like

     to boast that you don't even need to read the manual to use their

     computer program. The so called user friendly is probably what they

     intended to say, but somehow the impression they give is not. You type

     in some data, then you get some results. It sounds easy, but is scary."



     PipingOffice - Excel Spreadsheets for Piping Calculations

http://www.pipingoffice.us/<http://www.pipingoffice.us/<http://www.pipingoffice.\ us/<http://www.pipingoffice.us/>>



     Main site:
http://www.pipingdesign.com<http://www.pipingdesign.com/<http://www.pipingdesign\ .com<http://www.pipingdesign.com/>>

     Yahoo! Groups Links

   [Non-text portions of this message have been removed]



   PipingOffice - Excel Spreadsheets for Piping Calculations

http://www.pipingoffice.us/<http://www.pipingoffice.us/>



   Main site:
http://www.pipingdesign.com<http://www.pipingdesign.com/>

   Yahoo! Groups Links

[Non-text portions of this message have been removed]



PipingOffice - Excel Spreadsheets for Piping Calculations
http://www.pipingoffice.us/

Main site: http://www.pipingdesign.com

Yahoo! Groups Links

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