RT vs Design 1

[fazel1]

in ASME secVIII there are some rules to determine the amount of radiography by joint efficiency. But what should we do about the amount of radiography if we want to design base on ASME B31.1?

 

[metengr]

You follow the rules of ASME B31.1. For establishing minimum wall thickness of the pipe, you do have weld joint efficiency factors (see Table 102.4.3).

Regarding RT of finished pipe welds, there are specific examination requirements in Chapter VI, Table 136.4 that pertain to design pressure and temperature of the piping system.

 

[fazel1]

thank you dear metenger , but the joint efficiency which is defined in table 102.4.3 is for longitudinal weld of pipes in the production stage. what about the circumferential welds of pipe to pipe joints?

 

[FIF99]

Hi,

The joint efficiency factor will result, if less than 1.0, in a thicker wall, so the joint factor will also be effective as safety factor for the circumferential joint.

Additional inspection requirements for these joint welds should be found in the end users specification (fabrication, testing and assembly specs), or the relevant design code (such as ASME VIII or B31.1), or authority requirements.

Regards.

 

[metengr]

fazel1
For butt welds, it is assumed that you will exhibit full penetration, and it is typically a single-vee weld joint configuration. For all butt welds in piping, you need to use Table 136.4 of B31.1 to determine nondestructive examination or inspection requirements.

 

[fazel1]

hi,metenger
table 136.4 defines the amount of NDE after design . but there's no relationship between the amount of NDE and thickness in ASME B31.1. As you know in SecVIII div1 there's a frmula which relate the the thickness to the amount of NDE, but there's no such formula in B31.1 for circumferential joints of pipe to pipe.

 

[metengr]

Yes, this is true. The only relationship between NDT (RT) and the minimum wall thickness formula in B31.1 for piping is the efficiency factor "E", which applies to a long seam or spiral seam weld joint design and not a circumferential butt weld joint design.

I believe the reason is that circumferential butt welded joints that are full penetration in piping are as strong as the pipe base material and are under the influence of bending stresses (secondary stresses) versus hoop stresses (primary stresses) from internal pressure. Long seam weld and spiral weld joints are under the influence of hoop stresses, thus, weld joint design is critical.