Tensile Test Failure in Weld Metal

[zacharialamsyah]

Dear All

In tensile test, Failure or Break should occur in Base Metal, because the Weld Metal shall have greater strength than weld metal.

But, when i searching in some reference and even occur in my fabrication, failure could be located in Weld Metal and the result was OK (acceptable)

What limitation and criteria so failure on Weld Metal in Tensile Test can be acceptable?? (It's bothering me)

Thanks for your response and answer

Regards
Zachari Alamsyah

 

[weldstan]

As long as failure occurred at a tensile strength greater than or equal to the minimum specified tensile strength of the base metal, it's OK. The actual base metal tensile strength may be considerably greater than that of the weld metal.

 

[metengr]

Look at ASME Boiler and Pressure Vessel Code, Section IX, excerpt below, which supports the recommendation by weldstan

QW-153.1 Tensile Strength
......In order to pass the tension test, the
specimen shall have a tensile strength that is not less than
(a) the minimum specified tensile strength of the base
metal; or
(b) the minimum specified tensile strength of the weaker
of the two, if base metals of different minimum tensile
strengths are used; or
(c) the minimum specified tensile strength of the weld
metal when the applicable Section provides for the use of
weld metal having lower room temperature strength than
the base metal;
(d) if the specimen breaks in the base metal outside of
the weld or weld interface, the test shall be accepted as
meeting the requirements, provided the strength is not
more than 5% below the minimum specified tensile
strength of the base metal.
(e) the specified minimum tensile strength is for full
thickness specimens including cladding for Aluminum Alclad
materials (P‐No. 21 through P‐No. 23) less than 1/2 in.
(13 mm). For Aluminum Alclad materials 1/2 in. (13 mm)
and greater, the specified minimum tensile strength is
for both full thickness specimens that include cladding
and specimens taken from the core.

 

[davefitz]

There may be some exceptions to the classic criteria for the case of some newer creep strength enhanced alloys. The weld metal may be stronger than the base alloy at the elevated operating temperature but perhaps not at room temperature.

"Whom the gods would destroy, they first make mad "

 

[zacharialamsyah]

Ok I got the point..Failure in Tensile test can located in weld metal and also base metal...The acceptable tensile test is depend on the value of Tensile Test

But If we use Qualitative method only, ignore the value of Tensile stress (quantitative)...The tensile test failure (break) should be located on Base Metal, right?

 

[weldstan]

You cannot ignore the minimum specified tensile strength of the base metal.

 

[Guest102023]

Failure within or without the weld deposit is not a concern.
Section IX reduced section tension tests are designed to try and force failure in the weld zone, hence the very small dimension (1/4") of base metal permitted outside the weld toe on either side. Exceeding this actually puts you at a disadvantage in the case of slightly under-spec base metal.
The Code allows for the unlikely occurrence of slighty under-strength base metal. Metengr has reproduced all of the applicable rules w.r.t. minimum strength.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[FennLane]

Tensile Testing is not the most searching of tests depending of the properties you require from the finished component.

I think that we need to bear in mind tensile tests at room temperature do not always reliably indicate how a component will behave at low temperature or when dynamic loading occurs.

If the failure occurs in the weld I would be interested in the nature of the failure and its ductility compared to the parent materials regardless of strength.

Brittle welds may also be relatively strong when loaded slowly but fail catastrophically when there is an impact. This could mean slow monotonic testing could cause failure in the base metal but failure at a weld when a part is used outside in the cold and subjected to impacts.

I worked in the Boiler Industry for around 10 years and was responsible for Weld Procedure Development for both Pressure Vessels and Pipework.

We always tested welds using Tensile, bend and impact tests and for the last few years that I was involved also looked at CTOD and other Fracture Toughness testing to consider fitness for purpose.

I think a tensile test failure in the base metal is a good first approach but the materials being welded, the type of loading and the components duty all need thinking about if there is no developed procedure.

 

[Guest102023]

FennLane,
I have often wondered why welding engineers must repeatedly prove the properties of materials that have been thoroughly tested at the mill.
A PQR basically examines whether the welder has a pulse, is not inebriated, and has a modicum of skill.
The only two times I have had weld tensiles fail on me were due to gross casting defects in base material and poor welding.
.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[FennLane]

As a metallurgist that spent 6 years working in a steel mill, 7-8 years in Power Station Boilers and Pipework, 5 years research in Elasto-Plastic Fracture mechanics and the 25 years selling material testing machines (tensile/fatigue etc., etc)I would always worry about Mill Test certificates when used to assess materials that are used for Safety Critical applications.

The fact that a mill certificate implies thoroughly tested seems a bit if a stretch.

We introduced a range of computer controlled test machines in the mid-Eighties and the first question we were asked by a typical end-user (steel mill) was how do we 'edit' the results.

The reason for this question was simple and the explanation always given straightforward. "If the material only just fails we need to change the result so it just passes". The end user always insisted that they would only do this when they 'knew' this would not cause any problems.

I thought in this modern world of QA and ISO9000 that obtaining a signed concession was the correct approach.

Despite this the point I was making that depending on the duty of the weldment being considered simple tensile tests are not always searching enough.

Having run a three year programme testing welds in Grade E Drill Pipe tensile testing proved to be the least searching compared to Charpy Impact and bend tests.