Proper material grade selection 1

[akbari1358]

Hi all,

The attached pic is material section of a pig trap data sheet. Does anyone know why the material grade changes by changing the size? and is it possible to select same grade for all sizes?

Best regards,
Akbari

 

[BigInch]

As pipe diameter goes up, stress increases when using the same wall thickness. They are probably trying to use the same wall thickness, or as nearly possible, or as thin a wall as possible, hence higher grade material is required with larger diameters.

 

[weldstan]

It is simply more economical to use the higher grades to thin the wall down as diameter increases.

 

[akbari1358]

As far as I know using higher grade especially for high pressure system is always more economical due to decreasing the thickness of the wall; hence why the higher grade is not used for all diameter not only for pipes but also fittings and flanges?

 

[BigInch]

If small diameter pipe used high grade material, it would have an extremely thin wall, making it unsuitable for mechanical forces, wind, soil, shipping and handling, or gravity loads.

The numbers following the WPHY and F specify the grade for fittings and flange materials.

 

[MJCronin]

akbari,

1) Pipe fittings and flanges ratings for particular piping systems are selected based on different rules than for piping

2) Due to manufacturing limitations, not all piping materials are offered in all pipe sizes.

3) Have you discussed this with the engineering author of the pipe spec or is this spec a document from another company ?

4) As explained by BigInch, there are valid reasons to make small bore piping thicker than the minimum required by pressure alone.

MJCronin
Sr. Process Engineer

 

[LittleInch]

For pig traps it is important that the ID of the minor barrel matches the pipeline, which is often a higher grade material than something like Grade B or A105.

After that though it really doesn't matter and the person who created that list is thinking too hard and also being too prescriptive.

Unless your flange is directly connected to a pipe with higher strength, then you should just use the cheapest material available, e.g. all the nozzles and piping coming off the pig trap can be Grade B / A105 as can the Major barrel, providing the ID is still Ok.

You can find that getting pipe with a higher grade / strength is straightforward, but getting flanges and other fittings can take more time & cost more.

otherwise the general philosophy is as described by other above.

Note that A694 material is not included in ASME B16.5. You need to specify that these flanges should be supplied / designed using ANSI/MMSS SP-44 (flanges) and MSS-SP-75 (fittings). The dimensions are the same as B 16.5 / B16.9, but the higher strength materials are included. A plus point is that the pressure/temperature ranges are higher than B16.5...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.