p1 to p1 material using p4 electrode

[PMCap]

I have a Section VIII, Div. 1 vessel. I plan on welding P1 to P1 carbon steel material which has a type P4 liner. At the welds I plan on using a P4 material backing bar and P4 type weld material to maintain the integrity of the liner.

Question: Is it a code requirement that I perform Post Weld Heat Treatment or am I exempt as I am welding P1 material to P1 material?

 

[metengr]

PWHT is a function of nominal thickness as defined in ASME Section VIII, Div 1. Hint - look at UW-40 (f) of Section VIII, Div 1 to understand nominal thickness.

Then review Tables UCS-56 for P-No 1 and P-No 4 base materials. Assuming full penentration groove welds for the P-No 4 liner material, you can determine which of the two base materials controls the PWHT requirement. Looks like the liner being P-No 4 base material requires PWHT per UCS-56.

 

[PMCap]

Thanks, but as the liner material is not part of the code pressure boundary this should not govern the PWHT requirement or am I missing someting.

Also, in a case where I do not have a liner but just a P4 backing bar and weld the P1 to P1 material using P4 weld would I have the PWHT?

 

[metengr]

PMCap;
Sorry, but I am now confused by your post. Is the liner being joined to the P1 base material after the pressure boundary vessel welds are completed using carbon steel filler metal? Or is the liner integral with the carbon steel plates (roll formed cladding) and you are performing a combination weld of carbon steel to join P1 and using Cr-Mo filler metal to butt weld the liner? This information would help to ensure a proper response.

 

[PMCap]

metengr - Let me start by saying how please I am that you are addressing my issue as I have read you past responses that have helped many others with Code issues.

I restoring a degraded nozzle (thinned due to flow accelerated corrosion) on a Section VIII,Div. 1, vessel. Restoration will be by encapsulation of the existing nozzle to provide a new Code pressure boundary without removal of the existing degraded nozzle.

The encapsulation component (EC)is P1 carbon steel of 2-piece split nozzle configuration with an inside diameter larger than outside diameter of the degraded nozzle. All parts of the EC are constructed of 3/8" material. The EC replaces the degraded nozzle as the Code pressure boundary.

EC end closure parts are full penetration welded to EC nozzle parts. EC enclosure parts would then be full penetration welded to existing pipe above the degraded nozzle. Pipe above nozzle is P4 material, not degraded, and B31.1. Weld to pipe is exempt from PWHT requirement due pipe and EC end plate thickness (< 1/2") and their carbon content.

EC is lined with P4 material that is attached by fillet and plug welds.

Welds between the 2 halves of the EC, between the vessel shell and the EC, and between the EC end plate to pipe are all full penetration.

I want to maintain the integrity of the P4 liner material which is not subject to degradation by flow accelerated corrosion.

I use backing bars on the welds joining the two halves of the EC components together (nozzle and end plates). Welds between the EC and shell (1/2" thick P1 material)and the pipe (P4 material) do not have backing bars.

I would like to make all welds using P4 weld material so that the lining and backing bars on the inside of the EC protect the inner surface of the carbon steel P1 EC from direct steam impingement should the pressure boundary of the encapsulated degraded nozzle become breached.

Question:

As I read the Code - for Section VIII, Div. 1 pressure boundary material, welds between P1 to P1 material of less than 1 1/4" thick are exempt from PWHT.

However, as I am using P4 weld material - do the weld material and weld thickness govern over the EC material parameters in determining PWHT requirements? I can find no Code direction nor Code interpretations regarding this issue.

Thank you in advance for any advice you can offer.

 

[metengr]

PMCap;
First off, thanks for the kind words. I figured the devil is in the details, which is why I became confused with your original post and response. Not an easy problem because of FAC.
By the way, this is considered a repair to an existing vessel, and as such, the National Board Inspection Code or API would be most applicable versus using the Code of Construction. I have seen this encapsulation concept when it was presented to the NBIC main committee some time ago for acceptance. The Code is silent on this but I do remember a number of Chiefs did not support the concept.

So, first off let me offer some advice;

1. You should have this repair reviewed and approved by the Jurisdiction or regulatory agency before you do anything. Also, the insurer of the vessel should be involved for concurrence.

2. If you have concurrence, I would use carbon steel filler metal to weld all of the EC full penetration welds and weld between the carbon steel shell and that of the P4 pipe. If you have Cr-Mo liner material projecting slightly into the weld root region, there should be enough dilution from weld root tie in to provide the minimum chromium content needed to prevent FAC. All you need is greater than 0.10% by mass content to significantly increase FAC resistance. This would certainly apply to the P4 to P1 nozzle weld. Once the root is pulled between the P4 to P1 butt weld, there will be chromium in the weld root from dilution with the adjacent P4 pipe material.

Last question - Has the shell surrounding the original nozzle been evaluated? If not, this better be performed before any weld repair is executed.

 

[metengr]

PMCap;
Forgot to include the most important answer to your question now that I fully understand your thought process -

If you review ASME Section VIII, Div 1 UCS-56, for P-No 1 base material, look at Note 5. This note applies to welding of cladding or a corrosion resistant applied lining. In this case, your Cr-Mo liner is being used as a corrosion resistant liner, and as such you can use Cr-Mo filler metal to tie in the root, and to fill the weld joint use carbon steel filler metal with no PWHT.

 

[Duwe6]

Agree with all the above. And metengr gives the best repair method: 1 layer of P4 filler, then switch to a top-grade P1 filler to complete the weld. No PWHT required. Additionally, the P1 filler will stress-relieve most of your P4 layer, possibly all of it depending on the heat input and weld-bead overlap.

If it was my nozz, and Engineering forced me to weld all the way out with P4, I would PWHT that weld, or use a temper-bead welding sequence. P4 really needs PWHT, whether it is basemetal or weldmetal.

 

[PMCap]

metengr and Duwe6 - Thank you both

yes - jurisdictional and Code Inspector concurrence to use this restoration method as an Alteration is always obtained. All work is in compliance with NBIC requirements. EC components are Code shop designed, constructed and U-"PART" stamped. Installation is by "R" stamp organization


I appreciate and like your suggested method of welding such that FAC resistance is maintained at the weld joint.

Just for further clarity - I have been told that welding of 2 different P number materials should always be from a higher to a lower number (i.e P4 can be welded to P1 but not P1 to P4) -to avoid cracking. I don't know if this is a Code requirement, general industry good practice, or would even apply in this case as we would only be welding the root pass using P4 weld material.

If you guys don’t think I’ll have a root pass cracking issue – then your suggested welding sequence will be brought to the powers to be for serious consideration.

P.S. –I have the same issue where I use stainless P8 liner material on several applications. Would your recommendations also apply if I used a P8 stainless liner – P8 backing bar and P8 root pass?

 

[metengr]

I have been told that welding of 2 different P number materials should always be from a higher to a lower number (i.e P4 can be welded to P1 but not P1 to P4) -to avoid cracking.

Not true for the Cr-Mo to carbon steel combinations. This only applies to high Cr materials (309, 308) where the dilution of chromium with carbon steel will result in an intermediate alloy composition, which is potentially air hardenable to form martensite - around 5% Cr or higher. Welding 3% Cr or less steels to carbon steel can be done in any order.

 

[PMCap]

metengr - Thank you very much - I understand what you are saying and appreciate your expertise and having taken the time to clearly provide me with answers to my questions.

 

[Duwe6]

Again, metengr is spot-on. I have run into the "gotta match the highest mat'l" horse-pucky in several Code-certified vessel shops. Just increases preheat, usually mandated PWHT, and achieves nothing. This imagined requirement is just an 'old welders tale', with no basis in fact for carbon steels.

The P1 is still P1, and will limit the max temperature and allowable stress of your finished transition weld. If there will be enough welds to make it worthwhile, I sometimes use an intermediate-strength filler - split the difference between the two materials. But on P1 stuff, a top grade of E7018, like AtomArc is my go-to rod. If you can make a successful PQR [within the ASME mat'l limitations] your filler choice is valid.