Visual Weld Inspections: 1

[smitty9898]

I’m surprised I have not found this topic elsewhere on eng-tips. I'm trying to find out if there are any books that explain structural consequences from weld deficiencies. I will be looking at visual inspection and ultrasonic inspections soon, and I need to know what to reject and/or accept. I’m looking at steel framed building structures. Are there limits in AWS D1.1 that state the amount of porosity or undercut that is acceptable?

Does porosity create a weak point in the weld that could eventually lead to a crack? What about conditions that will reduce the life of the weld?

The obvious solution is to determine the reduced cross section of the weld, and see if the capacity is still acceptable.

From my limited experience, it seems as the SE will ultimately accept or reject the weld? The well inspector will just tell you what is wrong with it, but they wont necessarily access the impacts of the defects on the structural capacity. Any help would be great!

 

[metengr]

smitty9898;
Most Codes of Construction provide guidance on acceptance criteria for weld defects in components. So, you are not alone or are working in the dark.

I'm trying to find out if there are any books that explain structural consequences from weld deficiencies.

Try and Google several key words related to weld defects and failure of welded components, you will find plenty of information.

Does porosity create a weak point in the weld that could eventually lead to a crack? What about conditions that will reduce the life of the weld?

It certainly can, because the tolerance of porosity in welded structures is dependent on application, and type of loads in service.

 

[ndeguy]

KE Easterling's "Introduction to the Physical Metallurgy of Welding" whilst principally an academic text book for welding engineers, has a couple of closing case studies which highlight the potential lethal consequences of an ill-thought out welding strategy.

6 passengers lost their lives in The Ramsgate Walkway Disaster. Google it - it is widely covered on the Web.

For easily-accessible, beautifully-written materials and structural science books for the layperson, Prof J E Gordon's "New Science of Strong Materials" and "Structures" are well worth obtaining even though they do not deal specifically with welding. But after reading them you will certainly understand the theory behind why embedded porosity is generally harmless but planar surface-breaking defects are potentially lethal.

Informed reading smitty!

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[gtaw]

You may want to consider attending a class offered by the American Welding Society call the "CWI Review" or consider the course "Practical Welding Technology" offered by the American Society of Mechanical Engineers.

The AWS course is intended to prepare people to take the AWS Certified Welding Inspector's examination.

The ASME course is directed more toward the engineer that has to have a better working knowledge of welding and how to avoid problems such as defects, the problems that result from defects and how to avoid metallurgical problems.

AWS has a class in San Antonio, Texas this week starting on Tuesday. The AWS D1.1 code is covered starting on Sunday (a little late to get an airline ticket to Sunday's class).

ASME's course in offered in November in Orlando, Florida.

A course offered by International Business and Engineering Consulting (IBEC), Caracas, Venezuela titled "Fundamentals of Welding Engineering" is also a good course. It is taught in both English and Spanish.

Defects such as undercut, overlap, porosity, etc. will influence the service life of a weld. Cyclic loading will often result in a crack initiating at a weld discontinuity more quickly than a static load. The discontinuities act as stress risers and tend to concentrate the stress at the discontinuity.

Best regards - Al

 

[smitty9898]

Metengr: Do you know what specific sections of the building code or AWS code that state the acceptability of weld defects??

Ndeguy: I will check those books out at my University’s library

Maybe I stated my question incorrectly. I’m looking for documentation on strength reductions due to weld defects?? It may be as simple as reduce the cross sectional area of the weld.

I’m also interested in finding a specific AWS reference stating acceptable levels of porosity, undercut, etc., from visual inspection findings? I specifically deal with structural steel buildings. Thanks!!!!

 

[metengr]

Metengr: Do you know what specific sections of the building code or AWS code that state the acceptability of weld defects??

Review AWS D1.1 Structural Welding Code Steel -
Part 6 Inspection, and other parts.

smitty9898;

I’m looking for documentation on strength reductions due to weld defects??

Strength reduction factors (SRF's) are normally assigned by Code committees based on the assumption that cast material (welds or actual castings) contain some level of inherent flaws, in comparison to wrought material, which are assigned a value of 1.

Defects, like porosity, cracks, lack of fusion and inadequate penetration are treated separately as stress risers that could result in crack propagation in service. Acceptable flaw sizes are listed as acceptance criteria based on past experience and testing.

 

[ndeguy]

I dont think it is as simple as you propose Smitty, that is the remanent life of a structure being proportional to its cross-sectional area. Unless the structure is under simple non-cyclic loading, perhaps.

However cyclic loading usually plays a role and in this case Gordon demonstrates through simple mathematics that the stress concentration factor of a material discontinuity increases exponentially with decreasing tip radius. So for the same remaining ligament height in a material under applied stress, a blunt-tipped defect will not propagate as rapidly as a sharp-tipped defect.

In some fatigue situations the remaining life of a structure has been lengthened by radiusing the toes of welds to remove any sharp re-entrants.

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[henri2]

Smitty9898, I concur with GTAW's advice about taking an AWS CWI seminar. Although the primary goal is to prepare candidates for the CWI exam, some of the instructors go beyond that goal and delve into the materials engineering aspects of welding.

The 40 hour seminar is in three segments, namely: code clinic, fundamentals, and practical

In the fundamentals portion, depending on the instructor, topics may deal with: relationships between materials (base metal, filler metal etc), fabrication (cutting, joining, PWHT etc), micro and macrostructure, and resulting properties will be covered depending on the instructor. The instructor I had started going into stress intensity factors and other topics related to fracture mechanics, but he quickly realized the audience he was preaching to, were not that interested....and he got back on track.

Another excellent series of seminars is offered by Robert Shaw of Steel Structures Technology Center

http://www.steelstructures.com/

Bob will certainly get into alternative acceptance criteria. This is useful information for design engineers who have to make a call on an item which does not satisfy D1.1 Section 6 requirements. FYI, D1.1, Table 6.1 provides the VI acceptance criteria.

For UT, both Hellier and Krautkramer offer excellent Level 1 and 2 courses. Other beneficial NDT courses for structural steel welding are: MT, PT and RT Interpretation

 

[deanc]

May find a link or two here:

http://www.khake.com/page89.html

Also ANSI/AWS B1.11 Guide for the Visual Inspection of Welds

 

[deanc]

One more:

http://www.jflf.org/pdfs/papers/qua...ring weld quality in structural applications'