Boiler Terminal Welds - Governing min T

[wizster]

B31.1 clearly states that terminal points themselves (e.g., steam line connection on a header) are considered part of the boiler external piping. However, the code does not clearly define what material may be included in the terminal point.

My question is: can I include the counter-bored region of a weld preparation on the boiler fitting (Section I) side of the connection as part of the 'terminal point', or does the terminal point end at the fusion line of the weld?

The problem arose when NDE was performed on existing terminal welds. Low thickness readings were observed both sides of the weld, due to the counter-bore machined at the weld prep during original construction. Now what should we consider as the governing min T - Section I or B31.1 calculation? Min T is met on the fitting using a B31.1 calculation, but not by Section I (reason: boiler design temp at header is 1035 F, whereas piping design temp is 1005 F).

 

[metengr]

In reviewing ASME B&PV code, Section I, Figure PG-58.3.1 or 2 depending on the type of steam generator, it is my understanding that the boundary for the boiler proper ends at the nozzle weld prep (this is considered the end of the boiler proper). ASME B31.1 assumes technical responsibly for the weld and piping under administrative authority of ASME Section I, until the first isolation point.

You would need to either butter the weld prep region on the boiler nozzle and re-machine or extend the weld cap over the counter bore region on the boiler nozzle side of the weld to increase wall thickness to meet Section I minimum wall requirements.

As a side note to all this, what is your actual operating temperature for the steam line? The difference between 1035 deg F (boiler) and 1005 deg F (piping) is significant. Is the design temperature of 1005 deg F for the steam line adequate for your service conditions?? Normally, design temperatures for main steam or hot reheat piping are selected 10 to 20 deg F above normal operating temperature in the event upsets occur in service.

 

[ApC2Kp]

wizster,
Most people would say the Section I Code applies to new construction, and would not apply to existing welds in the field, even if it is the original weld for attaching BEP piping to the boiler. The opinion of AI will determine.
Question: Is the terminal point that you are examining be located on the boiler to BEP end, or is it at the BEP to NBEP junction? There is less of a question for a weld joint on a new boiler still in the fab shop, that would require the AI approval. A new field assembled boiler would get the AI involved as well. The AI probably would not get involved with the BEP to NBEP junction.

 

[metengr]

Repairs to boilers in service falls under the National Board Inspection Code (NB-23). This code specifically states that weld repairs shall be performed, as possible, following the requirements in the original code of construction. Yes, the AI will and must be involved with Section I components and B31.1/Section I components.

I will tell you this, for issues like minimum wall thickness calculations for pressure-retaining items, the design equations in the code of construction will prevail new construction or otherwise!

 

[wizster]

First thanks, metengr, for the super quick response. I am handling this during a short duration maintenance outage, so we already decided to extend the weld cap to resolve the issue, but your input is greatly appreciated.
The actual operating temp (as obtained through plant historian) is typically 950 to 980 F so, yes, the design is sufficient for the service conditions.

This is drum-type boiler and the connection is hot reheat line (BEP) to a reducer attached to the reheat outlet header tee (boiler proper components). I am in agreement with metengr, where the code of construction must be used for such assessments.

 

[ApC2Kp]

To wizster, and to metengr,
The solution was easy, and we agree that the AI should be involved to accept the repairs.
I should not have made it sound as if the Sec.I Code was no longer valid for equipment in use. The basic design equations, fabrication and inspection requirements still have application. My point is that the minimum wall thickness calculations are for a part with actual thickness so that zero mill tolerance of new pipe would be included. Also the corrosion allowance applied to a new design could be reduced to some smaller value, even almost zero corrosion allowance for anticipated replacement near term. So it provides a little more cushion in remaining wall thickness. Sometimes a repair ends up creating more headaches with testing and inspection, and justifying no action is better.
For the weld cap added, I suppose in-process visual exam of the repair exempted it from RT or MPT/PT. Re-hydrotest of the weld was probably not required. Since this is on reheat line, and material could be P11 or P22, was a PWHT done?

 

[wizster]

Yes, sometimes no action is better than repair. Things change real fast during a shutdown. We contacted the AI just after my last note on this forum and resolved the issue - weld to be left as-is until the next opportunity to change out the reducer, or correct the internal profile. It's been running like that since 1974 and full NDE (UT, fluorescing MPI, replications) revealed no problems.
If repair were required, we were looking at temper bead, since it was only a cap pass repair. Material is P22. NDE would have included MPI and in-process exam (and possibly RT - dependent on the chief inspector's call)

 

[ApC2Kp]

wizster,
Good to hear that things worked out OK with your AI.
The 1974 Code likely would have accepted the wall thickness with the prior allowables. See thread292-114837 about A335-P11 de-ratings of current allowables ('similar' for P22), and some good history provided by metengr.