Allowable thickness for restoring wasted wall thickness of pressure vessel

[Mateeng]

Dear Fellows,
We are in process of repairing a pressure vessel which the wall thinning has happened because of corrosion. We decided to restore the corroded area using weld buildup.
I have refereed to NBC and API 510 to find the maximum thickness is allowable to be restored by buildup welding. In other words under which circumstances we must use flush patch or lap patch?
Does anybody knows the limit based on industry practices, regulatory association like ABSA, BCSA, TSSA or code and standard for in service pressure equipment.
Much appreciated for any thoughts and inputs.
Alireza

 

[racookpe1978]

Rather than look at a rule book, how thick is the PV?

How much area must be restored to original thickness?

Is this one area of destruction, or a wide area? How many sq units (inches or cm) need to be repaired?

What material?
Do you have certified welders and a certified welding process already in place?

 

[chicopee]

One rule that I am familiar with is that if the original thickness has not diminished by more than 50% than you can rebuild the thickness with weld overlays.

 

[TGS4]

Check out ASME PCC-2, Article 2.2. In there, paragraph 4.5.4 states that if the wall thickness is less than the diameter of the weld electrode, then the pressure component should be depressurized. In this Standard, there appears to be no maximum amount of weld-build up, as you asked for. However, racookepe1978 has asked some very valid questions that will guide you to your answer.

 

[Mateeng]

Racookepe1978,
Please see answer to your questions:
How thick is the PV? 05"
How much area must be restored to original thickness? 0.4"
Is this one area of destruction, or a wide area? How many sq units (inches or cm) need to be repaired?Around 5" by 5"

What material? A516-70N Sour services
Do you have certified welders and a certified welding process already in place? Yes

TGS4,
Is that correct ande5rstanding that "Thicknesses less than welding consumable diameter is in risk of burn trough"?

 

[Mateeng]

Racookepe1978,
My mistake. The corrcet original thickness is 0.5"

 

[racookpe1978]

Well there is ALWAYS a risk of burn through (by an unskilled worker trying to exceed his competence level, or by a good welder attempting to work too fast, or by a skilled welder trying to use too high a heat rate (amperage) or too larger diameter rod or too large a filler wire ...

But a skilled welder can join or repair almost any thickness metal by choosing the right diameter wire or rod and the right amperage and the right speed. Your "thumb rule" is both correct and incorrect. Do not let it become a "Thumb rule of law" rather than mere guidance.

Other things that he or she can change: "time" of the current => small, short "taps" of the current let the thin metal cool off before the next little bit is melted on. Longer arc distances help. Lower voltages help. Good gas flow helps cool the metal. Applying shield gas as a coolant to the back side of the base metal helps suck heat away from the joint.

On your PV, 1/2 thick wall is a modest thickness that is workable - even for a significantly deep repair over a modestly small repair area. Check that the weld area is preheated carefully, and that the irregular - and probably very dirty ! - bottom and sides of the repair area are ground completely clear of pits and tears and valleys, and are both chemically and mechanically kept clean. Clean about 1-1/2 inch to 2 inches (35 to 50 mm) around the repair area as well.