Pressure vessel repair 2

[Jayb1]

I have 0.250" thick carbon steel pressure vessel.
Original max pressure rating 90 PSI 320 deg. F
Actual operating 30 PSI at 270 deg F
Vessel has pitting approx nickel size diameter to 0.125"
deep. 1.Can metal be added such as bead welding to rebuild
or fill the pits as a temporary patch, permanant repair, or not at all?
2.If individual doing repair is certified would the vessel need recertification and or pressure test?

 

[stanweld]

NBIC and API 510 both permit such repairs (considered permanenet) to be made. Welding procedure used and welders must be groove weld qualified per ASME IX.

 

[metengr]

Most important, the repair organization better have an R-Certificate.

 

[Mr168]

Assuming the vessel does fall under NBIC jurisdiction, you would likely be looking at a non-routine repair (due to wall thickness), involvement with your AI throughout the process, and additional NDE at a bare minimum.

 

[r6155]

An alternative is Acoustic Emission Examination. Rapair may not be neccesary.

Regards

r6155

 

[ShwaZmoto]

Keep in mind the repair must be made in reference to the year and code by which it was designed, i.e. if it was designed under 1962 Section VIII Div 1 code, then it must also be repaired under that same code. Your R stamped ASME repair shop will know to do this.

Also, if the vessel is a PWHT vessel, then localized PWHT of the welded area (along with NDE) may be required to complete the repair. Alternatively, the vessel can be derated, although most shops will be very reluctant to do so since the quality of the overall original construction, along with the current condition of the vessel, will need to be scrutinized to avoid liability on their part. For these reasons, replacing the vessel with a new construction may be a viable alternative.

 

[metengr]

Keep in mind the repair must be made in reference to the year and code by which it was designed,

Incorrect.

 

[ShwaZmoto]

From "Pressure Vessels: the ASME Code Simplified,"

"When an alteration is made to a vessel, it shall comply with the section of the ASME Code to which the original vessel was constructed to conform."

The last R shop I worked at kept every single revision of the code dating back to the early 1900's precisely because of this requirement.

 

[metengr]

ShwaZmoto;
Are you talking repair or alteration???????????????

Second refer to the interpretation below from the NBIC for repairs and alterations.................

INTERPRETATION 95-19
Subject: RC-1000 General Requirements
1995 Edition
Question: When the NBIC references “the original code of construction,” is it
required to use the edition and addenda of that code as used for
construction?
Reply: No. The term “original code of construction” refers to the document itself,
not the edition/addenda of the document. Repairs and alterations may be
performed to the edition/addenda used for the original construction or a
later edition/addenda most applicable to the work.

 

[ShwaZmoto]

metengr,

You are correct. Engineers can do anything they want under U2(g), so as long as they are not in violation of local law and can convince their allied inspector to sign off on the repair or alteration. However, most reputable shops will not do this. At a minimum, the original ASME design code is referenced for design intent, material properties, and the original design stress allowances. In the particular R shop I used to work at, our boss/owner was a licensed PE with 30+ years of experience, and he required us to run calculations from the original ASME code by which the vessel or boiler was constructed. As you point out, it may not be legally required; however, it is prudent to do so, and most shops will do this and take a conservative approach.

This topic was also covered here in this forum:

http://www.eng-tips.com/viewthread.cfm?qid=278430&page=11

 

[metengr]

ShwaZmoto;

In the particular R shop I used to work at, our boss/owner was a licensed PE with 30+ years of experience, and he required us to run calculations from the original ASME code by which the vessel or boiler was constructed.

Here is some advice, and it has nothing to do with reputable shops or PE's with 30+ years of experience. Let me give you a very brief example of why the approach above is flawed. If you remember the Code committee revised allowable stresses downward for P-No4 base material, 1.25% Cr-1/2%Mo back about 30 years ago, and for a second time after the Mohave hot reheat pipe rupture. Do you realize that if one were to go back and use the earlier code allowable stresses for time dependent properties that this could result in premature failure from creep rupture due to a less conservative design?

As I stated, and will state again, the owner/user and repair organization should evaluate which Edition and Addendum of the code of construction results in the safest condition for a repair or alteration. Simply to refer back to the original edition and addendum is not necessarily the safest condition, as I pointed out in the example above. It is your choice.


EOM

 

[trottiey]

The general trend has been for design rules to get more restrictive over time, while more materials are allowed and allowables go up. So outside of Section II, using an older code is usually less conservative. In fact, I just worked on an alteration where we used an old code edition to avoid the minimum ligament rules that came into effect in 1992. Nothing prudent about that. (We proof-tested a replica to make sure, but the code didn't require it.)

 

[ShwaZmoto]

metengr,

"Simply to refer back to the original edition and addendum is not necessarily the safest condition"

I did not say that it was. I said:

"most shops will do this and take a conservative approach."

For carbon steel vessels and boilers, due to the decrease in the design factor from 4 to 3.5, in most regards, the older code is in fact the more conservative approach, and again, this is for carbon steel vessels as the original poster described. In your high alloy example, the more conservative approach would be to use the newer code.

 

[jte]

if it was designed under 1962 Section VIII Div 1 code

No such thing as Div. 1 in 1962...

I think y'all are in violent agreement. Most folks that I speak with are comfortable using the latest edition of the Code for its "newer, better" rules while using an allowable stress from either the original or latest edition - whichever is lower.

Having said that, I have also replaced heads on a pre-1998 vessel using the post 1998 allowables for physically identical (same material, same thickness) heads. I handled it as an alteration and used the excess thickness as additional corrosion allowance.

There can be a lot of gray area in making these calls.

Finally, let's keep in mind that in many cases, the 2/3 yield criteria governs over the 4 or 3.5 against ultimate so there may not be as much difference in allowable stress as people think.

jt

 

[r6155]

Please, read:

API RP 572
API 579
API 579 Fitness-For- Service Example Problem Manual
and ASME PCC-2

Jayb1, I insist on Acoustic Emission Examination for this pressure vessel

Regards
r6155

 

[CodeRef]

My $0.02 I agree with all opinions so far and would like to add my opinion as well.
The current NBIC defines "Original" as metengr stated. Take note that the Edition and Addenda specific dates are omitted. There should not be any disagreement here as to the intent. Here is the Definition from the NBIC:

Original Code of Construction — Documents
promulgated by recognized national standards
writing bodies that contain technical requirements
for construction of pressure-retaining items
or equivalent to which the pressure-retaining item
was certified by the original manufacturer.

Any limitations specific to Edition and Addenda dates are specified by the Regulatory Authority (i.e..NRC) and the Enforcement Authority (i.e...Jurisdiction) where applicable.


FAQ731-376 A question properly stated is a question half solved.