NDT on Feed Water supply 3

[fatcobra]

Gentlmen,
I am reviewing or specs for the feed water system(discharge), and have a common practice question. According to our contract specifications we are required to assit the owner in recognizing areas or systems that normally require NDT, even if not specified by code.(@owners request) My feed water line falls under ASME B31.1, The design temp is 334ºF, with design pressure of 3774 PSIG. The temp is low enough so that by code this does not require X-ray. However I have been on projects where the owner required X-ray, and some projects where it was not required. Would you classify the NDT on feed water systems as "common practice"

Thanks,

 

[dtn6770]

I think a better question would be how much x-ray inspection should be performed? To which I would answer, at least 10% of all buttwelds, given the service. Whether or not that amount is common, I don't know, but I've seen 2500 class hydrocarbon systems of carbon steel construction receive 100% x-ray.

 

[fatcobra]

I am leaning toward recommending 100% X-ray, simply because the pressure is high, and the temp is only 16ºF below Table 136.4 in ASME B31.1. However I need to make sure I'm standing on solid ground, as I would hate to be back charged for recommendation and implementation of NDT not required by code.

 

[fatcobra]

The phrase "common Practice" is in our contract specifications, under client notification. Basically refering to industry standards and common practices in similar instances.

 

[metengr]

Common practice, outside of B31.1 specific NDT requirements, in our contract documents is to RT approximately 10% of the butt welds from each welder(s). If the subject welds are clean, that is it.

 

[unclesyd]

metengr,
Putting you on the spot. What if one of the welds falls out due to defects. This is where I've seen and been involved in some hat throwing and table pounding arguments about the additional RT needed. What is the current thinking on this subject.

PS
All our feed water lines are 100% RT. All lines to the Power Boilers are inspected with RT on a 3/4 year period for erosion/corrosion.

 

[metengr]

unclesyd;
Have been down this road before with our mechanical contractors for piping and boiler tubing (field installation) at all of our Generating Stations. If we find defective welds associated with a particular crew or welder we immediately expand RT coverage on their work, and the welder must re-test (in other words they are typically sent back to the hall for another assignment).

 

[unclesyd]

When use the 10% RT rule problems will arise. That's why I like 100% RT.
Personally I think the inspection criteria has to be made clear in the contract in that there will be strict adherence to all aspects of the Piping Code of Construction not just selected sections. I suggested many years ago that preconstruction meetings beheld to specifically iron these problems out prior to commencement of piping fabrication. Not doing so has cost us time and money on several occasions. The company is just starting to have preproject meetings with each bidder concerning all aspects of QC and inspection, especially the welding. Even though construction companies have a copy of the required codes their lack of understanding of same sometimes borders on criminal intent.

 

[stanweld]

fatcobra:
"Common practice" with regard to NDE feed water systems has varied greatly during the past decade. In combined cycle power generating systems with fixed price contracts, it has been either 10% or none (mostly) on the over 30 such projects with which I have been associated. If you are the Engineer of Record acting for the Owner/Operator "common engineering sense" should prevail and guide your decision making, especially with regard to a supercritical steam generating system. If I were the Engineer advising the Owner/Operator in your case, I would specify 100% RT.

 

[fatcobra]

Stanweld,

I am not an engineer, I am a quality control manager. However the engineering on this project are all recent graduates, and have very little experience in the power generation industry. Consequently we are not only the erectors but also assiting the engineers.

 

[dtn6770]

Hit up your or your client's insurance agency; they should have an opinion.

Are there any third party inspector in the loop that you could get some insight from? I remember Section I requiring boiler manufacturers to have their fabrication procedures, as well as the design and material selection, monitored by a third party inspector. That authorized inspector is usually employed by an insurance company and is licensed by the National Board of Boiler and Pressure Vessel Inspectors.

From a liability stand point, I'd wager anyone not paying the bills will recommend 100% radiographic examination.

 

[metengr]

dtn6770;
Ah, dtn6770 you have it the nail on the head. As an owner's Engineer, I need to balance the cost of 100% RT versus selective inspection. I respect the opinions above. However, when it comes to going above and beyond minimum Code requirements one has to treat each project on a case by case basis.

It would certainly be easy for me to recommend 100% RT of the above because it reduces exposure to any liability. For a supercritical unit a higher percentage of welds could be evaluated (30%), versus only 10%. However, I work for an operating company, and project cost is very important.

 

[dtn6770]

metengr,

I did the owner's engineering gig for over 14-years so I know where you're coming from. Often it's a no-win situation; sticking with the theme of this thread, end-user management or project supervision may embrase Code compliant, but limited, NDE but if something goes wrong down the road with a weld that wasn't shot...it's the engineers fault for being too conservative.

It's fair to ask Fatcobra to review the applicable Codes and tender a non-binding opinion but at the end of the day his/her clients are going to have to make the final decision and assume any risk. At best it will be an informed decision that takes into accout safety as well as the short AND long term economic consequences.

 

[rmw]

This is OT but related to the topic. Your feed water temp is 334 F or C ? Sounds low for F. Normally on a supercritical system the FWP discharge is through the highest heater or maybe the last two in the string, but still the BFP suction is from the IP heaters and the pump suction is ~500F.

Even so, if the line you are working on is between the BFP and the last heater(s) you will have higher design temps to deal with downstream of the last heater.

rmw