Welding procedure qualification

[waqasmalik]

Hi all, I have question regarding minimum tensile strength requirement of a tensile test specimen for welding procedure qualification according to ASME Section IX BPVC. The base material i am using is aluminum 6061 T6. For this material the minimum tensile strength requirement as specified by the section IX is 24 Ksi, but, infact the strength of base material is higher( 43Ksi) than that of as specified. The same trend i observe in other grades of aluminium.

I am aware of the strength loss due to welding of aluminium in its heat treated condition because of partial annealing/overaging. Strength of annealed base material 6061 is 18 Ksi.I also know that after welding in heat treated condition,there must be complete reheat treatment to regain the lost strength in fusion zone and HAZ. But, then why ASME states that welding procedure will be qualified if the specimen ruptures at or above the 24 Ksi strength.?

Thanx all in advance.

 

[metengr]

Section IX states nothing about the specific strength requirement for aluminum. Acceptance of the tensile test is based on the following obtained from the actual tensile test results from tensile specimens removed from the weld coupon;

QW-151.3
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.

 

[waqasmalik]

Spec UNS ALLOY Min Tensile strength Welding P number
B345 A96061 6061 24 (165) 23

Metenger

The above specs has been taken from ASME section IX 2010 . Page # 121.

 

[waqasmalik]

AWS D1.2 quotes the minimum tensile strength of the tensile specimen be 26 ksi. Basically, i want to ask that what will happen metallurgicaly if tensile test specimen ruptures at value below 24 or 26. Strngth of base material is 43 Ksi.Specimens fail at HAZ.

 

[metengr]

Metallugically, you have over-aged the base metal in the heat affected zone. In this type of situation, (d) would apply

(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.

SO, you have 5% margin regarding the base metal heat affected zone regarding the MINIMUM tensile strength of 23 Ksi. ASME Code only concerns with minimum values and not values that well exceed the minimum value, so you cannot take credit for stronger material.

 

[waqasmalik]

Thanx metenger. I have two more questions if u dont mind plz.

1)The reference for 5% calculation would be 24 Ksi or 43Ksi?

5% of 43 is 2.15.
5% of 24 is 1.2.

so 43-2.15 40.85 and 24-1.2= 22.8 Ksi.

2) Why the minimum requirement of 24 is given? Of course we cannot use the production weld in this condition, we need to get it heat treated again to gain strength of 43 uniformly. Can't the complete strength be obtained after reheat treatment if tensile strength is less than 24, 20 lets say?

 

[metengr]

You need to go back and review the material specification because the minimum tensile requirement is from the material specification in accordance with specified heat treatment, and not Section IX or other published values for 6061.

The 5% would apply to the minimum specified tensile strength. In this case it would be 23 Ksi, per ASTM B 345. So, if the base material comes in at 30 Ksi or even 35 Ksi you don't use these values, the 5% value is based on 23 Ksi, if the failure occurs in the heat affected zone.