How to measure thickness of weld for inspection ASME Section I A250.2

[srijey]

Issues: maximum and allowable reinforcements are not defined; how to measure thick and thinner section welds are not known; whether the thickness of weld or plate includes crown and root penetration is not known; weld thickness t seems to be same as thinner component thickness; surprisingly ASME Section I A-125 defines the same letter ‘t’ differently!

Refer: page 205 of ASME Sec I A 250.2 terminology, ASME Sec V T-434.5.1 h) on page 47, ASME Sec I Fig PG-42.1 on page 36; Page 76 of ASME B31.3 Table 341.3.2; ASME Sec VIII Div 1 page 150 UW-51; ASME Section IX QW 191.2.3.
When the thickness of weld is defined in these sections (say Section 1 A 250.2.3), it's bit wordy and why not just say: Least of
a) Thickness of weld of Pressure retaining material
b) Thickness of weld of thinner of the sections being joined

 

[gtaw]

ASME references AWS A3.0 for terminology not included in the construction code. A3.0 defines the groove weld size as being the joint penetration. As such, the weld reinforcement is not included.

From a practical standpoint, the joint penetration of a butt joint cannot exceed the thickness of the thinner member when two different thickness are jointed together.

Best regards - Al

 

[srijey]

Thank you very much Al. Does that mean, in simple terms, weld thickness is same as the thinner component thickness at the groove or fillet? I'm also confused in understanding what is the thickness of weld of thicker section? ASME Section 1 A-250.2.3 terminology is bit confusing. Do you agree?

 

[gtaw]

The chain is no stronger than the weakest link. In most cases that will be the thickness of the thinner component in the case of a groove weld assuming the weld metal matches the properties of the base metal.

All bets are off if the weld metal is under matching, i.e., not as strong as the base metal.

In the case of a fillet weld, the strength of the weld is dependent on the shortest failure path, i.e. the dimension of the effective throat with no credit for the convexity of the fillet face. Most welding standards use the dimension of the theoretical throat as the determining factor when calculating the strength of the fillet weld. It is conservative, but the effective throat dimension is dependent on current used, diameter of the electrode, etc., so it is variable. AISC only allows the designer to take credit for the effective throat if SAW is used.


Best regards - Al

 

[srijey]

Thanks again Al. In this case, my reference ASME Section 1 A-250.2 is for the radiographic inspection - chiefly to determine the acceptance criteria. Is it not logical to measure the weld rather than component - just to make sure that stringent inspection - large area is covered? I mean acceptance is based on a fraction of thickness (refer A-250.3.2). Assuming that you may not have the section 1 handy, I quote the content: A-250.2.3 Thickness t. t is the thickness of the
weld, of the pressure–retaining material, or of the thinner
of the sections being joined, whichever is least. If a full
penetration weld includes a fillet weld, the thickness of the
fillet weld throat shall be included in t.
Hope I could make my question clear this time. I regret my poor language skill.

Jey

 

[gtaw]

No problem.

Every code is different.

Since sensitivity is a function of the material thickness, using the value of the thinner section/member means that the size of the discontinuity is based on the thinnest section. The thinner the section, the smaller the critical discontinuity.

Compare 2% of a member 50 mm thick to 2% of a member that is 25 mm thick. 2% of 25 mm is 1/2 the value of 2% of 50 mm thick. The bottom line is that the critical discontinuity of the 25 mm member is 1/2 the thickness of the 50 mm. In other words, they are looking for a defect that represent 2% of the material thickness. If the density of the film is darker (indicating reduced thickness) or if either the length or area of the discontinuity is beyond an acceptable limit the part is rejected.

For the sake of discussion, disregarding the code for a minute, consider a 12 mm hole in a 25 mm thick plate versus a 12 mm hole in a 50 mm plate. Clearly the 12 mm hole in the 25 mm plate is more detrimental than the 12 mm hole in 50 mm plate assuming all other dimensions and the magnitude of the loading is the same.


Best regards - Al

 

[srijey]

Thank you Al for the explanation. I meant exactly what you say - in my words 'stringent inspection' (refer A-250.3.2 where the acceptance is a proportion of t. That's not clearly understood in the definition of the terminology t in A-250.2.3. May I know what you interpreted from that paragraph? What is t (not to be confused with the same notation 't' appearing in A-125!)! Because this is a sampling parameter, by including allowable (or maximum?) reinforcement as per code see Table PW-35.1 in Section 1, the volume will be more and of course the acceptance will become lenient. All I need is: What is that t defined in A-250.2.3, how to measure it?

 

[gtaw]

Think of a butt joint between two members. One is 50 mm thick and the other is 25 mm thick. The weld size can be no greater than the thickness of the thinner member. Codes do not give "credit" for face or root reinforcement. Assuming the weld is ground flush with the adjoining surfaces, the thinner member is the weakest link. The weld is the same thickness as the thinner member, so it is the basis of determining which IQI is used and the size fo the critical indication.


If the weld is not ground flush and if the backing bar is left in place, a shim is placed under the hole type IQI or the wire type IQI is placed on the weld so that the "thickness" under the IQI is the same as the weld being tested. Still, the acceptance criteria is based on the thinnest component, i.e. the thinner member.


I hope I've addressed your question.



Best regards - Al

 

[srijey]

My interpretation of your answer: ASME Section 1 A-250.2.3 Thickness t. t is the thickness of the weld, of the pressure–retaining material, or of the thinner of the sections being joined, whichever is least. If a full penetration weld includes a fillet weld, the thickness of the
fillet weld throat shall be included in t. This definition is convoluted and is misleading because of the term 'weld'. To make it simple and clear, t is the thickness of the thinner section at the weld. This applies to both butt or fillet weld. I'm happy if ASME accepts such plain language and willing to correct this!

Just for the benefit of any other reader of this discussion, I'm listing below other 'related' code definitions of similar situation - inspection acceptance criteria.

Page 76 of ASME B31.3 Table 341.3.2 : For groove welds, height is the lesser of the measurements made from the surfaces of the adjacent components; both reinforcement and internal protrusion are permitted in a weld. For fillet welds, height is measured from the theoretical
throat, Fig. 328.5.2A; internal protrusion does not apply.

ASME Sec VIII Div 1 page 150 UW-51: t the thickness of the weld excluding any allowable reinforcement. For a butt weld joining two members
having different thicknesses at the weld, t is the thinner of these two thicknesses. If a full penetration weld includes a fillet weld, the thickness of the throat of the fillet shall be included in t.

ASME Section IX QW 191.2.3: t is the thickness of the weld excluding any allowable reinforcement. For a butt weld joining two members having different thicknesses at the weld, t is the thinner of these two thicknesses. If a full penetration weld includes a fillet weld, the thickness of the throat of the fillet shall be included in t.

ASME Sec I A -250.2.3 Page 205: t is the thickness of the weld, of the pressure–retaining material, or of the thinner
of the sections being joined, whichever is least. If a full penetration weld includes a fillet weld, the thickness of the
fillet weld throat shall be included in t.

ASME Sec V Fig T-434.2.1 page 47 Notes (h)
Weld thickness, t, is the nominal material thickness for welds without reinforcement or, for welds with reinforcement, the nominal material
thickness plus the estimated weld reinforcement not to exceed the maximum permitted by the referencing Code Section. When two or more
base material thicknesses are involved, the calibration block thickness, T, shall be determined by the average thickness of the weld; alternatively, a calibration block based on the greater base material thickness may be used provided the reference reflector size is based upon the average weld thickness.

 

[srijey]

I interpreted ASME Sec I A-250.2.3 as: Least of a) Thickness of weld of pressure retaining material; b) Thickness of weld of thinner of the sections being joined. However I took the definition of thickness of weld from ASME Sec V Fig T-434.2.1 page 47 Notes (h)
Weld thickness, t, is the nominal material thickness for welds without reinforcement or, for welds with reinforcement, the nominal material
thickness plus the estimated weld reinforcement not to exceed the maximum permitted by the referencing Code Section. Of course the contarctor likes this definition, but we, the owner, in an attempt to get stringent inspection, lowered the thickness of weld to the thickness of plate. The contractor argues that this is not code compliance. Whether Al's interprestation is supported by any code section?