Rewelded Thick Forged Alloy Steel Strength & Life

It should be neccesary a bit more information about the forged material grade and as supplied heat treatment.

Anyway, is quite common to repair welds on any material due to improper electrode composition as in your case or just improper storage of electrodes or a good welder in a bad day.

Usually this doesn't affect the behaviour of the part, but usually is in some way assured too by the welding procedure qualification which be at least includes a simulated repair and the total stress relieving heat treatment time must at least equal to the maximum total heat treatment time expected.

kind regards

Thanks for the response which matches what the manufacturer has proposed. One further statement and two queries:

I read this in some text-book, but don't remember now which, that the Heat Affected Zone (HAZ) in a narrow gap weld does not exceed ~1 mm. Is this true.

Is the HAZ uniformly distributed along the thickness of the weld seam in automated welding? Do you know, heard or have read about what the experience say or research has shown about this?

The HAZ is distributed through complete thickness.The width depends on the material and welding process. Just think that a definition of HAZ is that base metal zone, not melted but which have reached a temperature level which affected his metallurgical structure. So, even for the same welding process it's width can depend on the heat input, the thickness, etc (the thicker the part, the quickest the cooling rate and the thinner the HAZ)

To check the HAZ width in your case you may have a look on the procedure qualification tests if some macro/micrographs were made. If you haven't this information but have a free welded end, just polish it and etch it with nital 2 or 3 (A solution of 2 or 3 % nitric acid in ethanol) The HAZ should appear in a different grey tone than base metal.

Kind regards

The reason you are removing part of the base metal is to try and start the weld on a clean slate so to speak and to remove all of the original HAZ and alloy dilution from using a improper electrode during the previous weld. With any weld you are trying to match the chemical and mechanical chracteristics of the weld metal to the base metal and the weld should be stronger than the base metal. This is true in all types of material and is designed into the proper weld procedure. Being it is a thermal craker I would also assume that you are dealing with an alloy with a high amount of chrom-moly. It is often times required on chrome-moly alloy repairs to gouge out the old weld and then grind to below the HAZ being careful not to over heat the base metal and removing any metal that was affected by the heat from the original welding or gouging process. With these type alloys post weld heat treat is very important or you could run the chance of annealing or hardening an area of the base/weld metal without the proper PWHT. i am not sure why you have porosity though because the cause of porosity is usually caused by a contaminate that burns and displaces the shielding gas of the welding and allows oxegen from the air to touch the weld puddle and not merly an improper filler metal alone. IMO is probably a good thing that the porosity was found in the weld or you may have never known that the wrong alloy electrode was used in the first place.

pipewelder

Thanks for the response. I posted the following queries already:

I read this in some text-book, but don't remember now which, that the Heat Affected Zone (HAZ) in a narrow gap weld does not exceed ~1 mm. Is this true.

Is the HAZ uniformly distributed along the thickness of the weld seam in automated welding? Do you know, heard or have read about what the experience say or research has shown about this?

Can you help in these?

The first step is to ensure a fully qualified metallurgical engineer and vessel design expert consult and agree on the Weld Procedure' to be used in the repair. This analysis will consider all the pertinent information of materials, climatic implications, anticipated service conditions, welding technical details, welder training and certification requirements , weld repair test programs etc.

You certainly want to thoroughly test the weld repair procedure before attempting it on the actual vessel.

Since this is certainly a 'registered vessel' built to ASME or DIN or ?? specifications and has a data plate attached, the original designer and fabricator MUST be involved in designing and approving the repair procedure--including PWHT. If the location is in the U.S. the Process Safety Management law requires fully documented technical evaluation of this repair before it is attempted since this is a significant change to the equipment.

An improper repair could result in catastrophic failure. A proper repair will result in strength and service life equal to original intent or better. THoroughness in the technical evaluation and development of the repair procedure, planning of the repair program to the smallest detail, and complete quality control of ALL elements in the work are necessary to achieve the desired objective. Even a small transient deviation from the required condition may result in tragic consequences. A single defective or wet welding rod could lead to vessel failure.

Thanks for your valuable suggestions which are being taken in to account. You have mentioned some ASME/DIN Standards. I am not aware of these. Please be kind to give their reference numbers if they cover such repair work.

The manufacturer has engaged Designer's original vessel design and metallurgical engineers to give documented technical evaluation of the repair.

I posted the following queries already to other contributors, which are repeated below:

I read this in some text-book, but don't remember now which, that the Heat Affected Zone (HAZ) in a narrow gap weld does not exceed ~1 mm. Is this true?

Is the HAZ uniformly distributed along both the surfaces of the weld seam with the base metal in automated welding? Do you know, heard or have read about what the experience say or research has shown about this?