Manaway Davit Arm Made From Pipe 1

[roca]

A vendor of ours is purpose designing some manway davit arms from SA106 Gr.B pipe.
I requested that the -12.5% undertolerance be applied to the pipe - unless of course they do thickness checks to confirm actual pipe thickness.
The davit is for a 24"NB-600# + 5mm Weld Overlay blind flange (circa 570kg / 1250lbs).
Am I being too conservative?
Thanks

 

[r6155]

Inspect before and after bending the pipe.

Regards
r6155

 

[SnTMan]

I would hope a davit was not designed so closely that pipe tolerance was important.

Regards,

Mike




The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[jtseng123]

For 24"-600# blind, using A-106B, 3" Sch 80 davit arm is good. You don't even need to ask for calculation. Many companies or handbooks have davit standards to follow as well as PIP VEFV1117. It is too much by asking for calculation.

 

[EdStainless]

The SF on these is usually high enough that tol is not an issue.
I jsteng123 says, you can find 'pre-designed' versions of these.

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

 

[r6155]

Is a good engineering practice to consider pipe tolerance. Also corrosion, surface protection, NDE of welds………etc.

See ASME BTH-1A "Design of Below-the-Hook Lifting Devices" as a guide for davit (standard drawing as PIP or others configurations).

Regards
r6155

 

[oknow]

If this is for a ASME Section VII Div. 1 Code Item then I suggest to add the calculations (UG-22(c)) to the design package. It is often over looked by the Certificate Holder and the AI.

 

[JStephen]

Is there any code that specifically says what the allowable stress for that davit arm is?

My point is, if the design is based on somebody saying "Let's use...uh...18,000 psi!", that's great- but quibbling over the thickness tolerance is pointless, all they have to do is assume appropriately higher stress and they have the same design and you've both wasted some time.

 

[SnTMan]

JStephen, I wish I'd said that

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

1) @ oknow.
No calculations is required if all dimensions and materials are as PIP.

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES
In an effort to minimize the cost of process industry facilities, this Practice has
been prepared from the technical requirements in the existing standards of major
industrial users, contractors, or standards organizations. By harmonizing these technical
requirements into a single set of Practices, administrative, application, and engineering
costs to both the purchaser and the manufacturer should be reduced.

2) @ JStephen:

See PIP VEFV1107 / 18 and 19 “all thickness shown are based on 36 ksi yield strength”
See AISC for allowable stress.

Regards
r6155

 

[r6155]

According to AISC: Available strengths of round HSS and Pipe are listed in Manual Table 3-14 and 3-15. The tabulated properties and strengths of these shapes in the Manual are calculated using a design wall thickness of 93% of the nominal wall thickness.

Regards
r6155

 

[JStephen]

I'd be curious if the PIP standards were ever updated for the newer AISC standards.
Note that A106-B is a 35ksi material, not 36 ksi.
I expect the 93% is based on A500 structural tubing.

 

[r6155]

JStephen, you can contact with help@pip.org

Regards
r6155

 

[oknow]

@6155,

Your statement would not be acceptable to any accomplished AI/AIS or during a Audit/Review. Most davit arms have some sort of welding on the nozzle or flange (Code weld). If it is considered and applies in UG-22 then some sort of design justification is required. This is normally done by calculation but also have accepted tables from the Pressure Vessel Handbook or other engineering standard (JIS,GB BS).

 

[r6155]

@ oknow
Please, read in full the purpose and use of PIP -

http://www.pip.org

Regards
r6155

 

[oknow]

R6155,

A very nice web site but has no bearing on the ASME Requirements. There is nothing more to be said from my side on this issue.

Regards