How to Determine the Acceptability of Boiler Reheater Tubes?

There is no short-cut with safety.

UD15

It seems to me that you have alredy answered your own question. Non-conformance. If you still want to push it, backtrack to the Mfr. How did these out of spec tubes get out their door? Who bought them. Cover your own ass first and then, just as important, KEEP THIS PROJECT SAFE! Boilers are no laughing matter. Are you the engineer of record? If not, Find him!

Yes sir I am the boiler engineering manager for this project and have already rejected these tubes. I was thinking they might be some technical evaluation method eg remnant life assessment, grain structure analysis etc that can be done to see if the tubes are still fit for purpose in order to avoid the delay. The cost of the delay with penalties will definately go to the contractor.

I agree with you guys boilers are not laughing matter. This tube is subjected to 510 deg C and 4.2MPa

With risk assessment, these tubes may be used, and its remaining life can be calculated. But attention should be paid towards the nature of that grooves which cause a reduction in thickness.

I mean if that grooves are a sharp scratches, hence there is an actual risk for stress concentration at these areas at higher temperatures and cracks shall propagate. And in that case the tubes shall be rejected and reinstall a new.

And if that grooves are somewhat smooth, I think you can use that tubes, with short periodic inspection intervals and good monitoring for any changes while in operation.

Thanx Abdel. In my opinion there are not sharp scratches but you never know what the scratch lines realy look like. I am failing to paste the picture here.

Tube image

Thank so much Abdel. Will ask the contractor to do the risk assement and make a decision based on that. As for the groove see the picture below.

The grooves are caused by the ID Weld Bead removal and could be acceptable depending on a few considerations.

First, there is a minimum wall tolerance applied to your tube specification. When the tube manufacturer orders the strip that they plan on using, they have to order it slightly thicker in order to account for the tolerance of making the strip.

Second, by looking at your pictures, your tubes were manufactured using an induction coil welding process. This process creates a current flow along the edge of the strip between the coil location and the weldbox squeeze rolls. This section is called the 'V'. The current flow increases the temperature of the steel which is then squeezed together in the weld rolls.

As a result an internal and external weld bead is formed and then subsequently removed.

A point to consider is the width of the heated steel, referred to as the HAZ 'Heat Affected Zone' is wider than where the weld bead was removed. In the HAZ you will get what we Tubers call 'Heavy-Up' which increases the thickness of the steel adjacent to the weld as a result of squeezing the tube together while his portion of the strip is heated.

Considering the slight increase in original strip gauge to account for the manufacturing tolerance there, and the Heavy-Up adjacent to the Weld Zone during the tube's manufacture, you can safely assume that the wall thickness in the weld zone is thicker than the minimum gauge required by the spec.

The ID weld bead removal has varying acceptable tolerances applied to it depending on the spec it was manufactured to. For example (Flush +.010) infers that no undercut is allowable but a protrusion of .010 is acceptable. Your tubes however appear to have a Flush to min wall spec applied to the ID weld bead removal, where there can be no protrusion but can undercut so long as the thinnest section of wall remaining is not less than the original min wall spec applied to the tube.

So, my recommendation is to first check the spec to which the tubes were ordered and confirm what allowances are provided related to ID weld bead.

You still may have an issue as an incorrect value could have made it to the tube mill for your specific order. But, I wanted to clarify that tubes with conditions such as yours are common, especially where no ID weld bead protrusion is permitted, only flush to undercut.

If you find that your tubes were made with a Flush to Min Wall spec, you'll want to measure the thinnest par of the wall at the undercut and insure that it is equal to or exceeds the min wall spec of the overall tube.

Hope this helps,

JavaHead

Umm, yeah... so I just noticed you said they were seemless so the whole post I wrote above is mute... I should have read rather than just skimming and looking at the pictures.

Sorry.

Umm, yeah... so I just noticed you said they were seemless so the whole post I wrote above is mute... I should have read rather than just skimming and looking at the pictures.

Sorry.

Don't be sorry...There welded! I have seen this before, the tubes are going where???

These tubes were Drawn after welding, which make them look from the outside as if they were extruded. It looks from the picture that is the case. I would check the metallurgy from the location in question and find out who is getting paid to let these tubes find there way into the boiler.

Indeed they are, looking at the picture closer you can see where the 'heavy-up' in the HAZ is a bit more polished as a result of the drawing process.

So, that brings me back to my original post, if it is still readable.

First, the depression was caused by an ID Cutting ring and is not a gouge. Second, the thinnest portion of the wall in this area may still meet whatever min wall spec was provided. Third, there must be some boiler applications where HF Induction Welded Tubing is applicable as we run quite a bit of it for boiler applications. But we sell to service centers and only a few actual boiler makers.

So, I suppose the original purchase spec would clarify if only seamless tubing was permissible. If not… then these tubes may meet spec, both literally and functionally.

JavaHead

Most have answered in the negative, and I certainly agree with them........4.2MPa is not a pressure to stuff around with in steam systems.........or even lower pressures for that matter.

The tubes would/could be dangerous to use........that groove could possibly be a stress raiser........not good. I mean that is why we have standards, which will also include a built in safety factor for the component..........as someone said.........go outside the standards and shit can happen..........and it usually does.

I have had experience on marine boilers up to 8.3 MPa........and one thing we never did was take chances.......it may have been the last one.

If those tubes were used it could certainly aggravate tube wast as shown in this photo here, which could lead to this

A "leaky tube" and the boiler room is no place to be when that happens!!!

Also, just wanted to comment on your 6-months to a year lead time... not sure who you're buying these from, and I will attempt to avoid any direct advertising, but most tube mills have extra capacity right now and would love to have an additional order.

If it pans out that these tubes are not acceptable, I'm sure you'll be able to find some quite a bit quicker than that.

JavaHead

Thanx guys for all tha contributions. Actually there are multiple grooves around the inner circumference. Unfortunately the picture shows only one. To me it looks like a defective extrusion tool or poor lubrication during the process. I do not think I am going to take any chances with these tubes.

JavaHead I am buying these tubes from france and I am in South Africa that is why the lead time is so long. They also have to be manipulated before they are delivered to site.