Sandblasting For Prep of Pipe Fittings For TIG Roots

Date 06-18-2014 20:52

WPS says it all!!!!!!!!! That why it's there........ Why not run a grinder on it anyway , yourself....... If I'm welding it I fitt it and prep it like I want .....(or my helper does) :cool:

By ZCat

Date 06-18-2014 21:16

I've been grinding the lands down, but that stuff is on the inside, too; and sometimes you don't have access to it. The spools come to us already put together by the fitters.

By IowaCWI (*)

Date 06-19-2014 00:00 Edited 06-19-2014 00:42

Is there any chance these fittings are subject to mag particle or dye penetrant any time after sandblasting? I can think of a hand full of reasons why sandblasting should not be used as the final step in joint preparation. One of which is, the peening action of the blast medium very well could be embedding impurities into the base material. That may be why your root pass is turning out the way it is. You have to consider that the blast medium is probably reused several times prior to renewing it. And if it is being scooped off the floor and placed back into the hopper who knows what kind of impurities are getting put in with it. The reason why I ask if it is undergoing NDT after blast is also because of the peening action of the medium. Certain NDT methods are hindered by peening due to the fact that it covers up discontinuities.

Just my 2 cents worth from an NDT point of view. I am more than positive that some of the more experienced individuals on this forum can come up with some valuable information for you.

By Stringer (***)

Date 06-19-2014 00:58

Never heard of such a thing. Probably for good reason.

By IowaCWI (*)

Date 06-19-2014 01:04

Be more specific Stringer

By IowaCWI (*)

Date 06-19-2014 01:46

If it is any help, this topic was discussed some time ago in the "technical" category of this forum. Original post was made by Sloppyjoe86.

By Stringer (***)

Date 06-19-2014 12:03

Well, it doesn't sound like a sound practice if it's dulling edges and embedding contaminants.

By js55

Date 06-19-2014 12:18

Blasting would not be considered preparing a bevel. Its preparing a surface.
I do not see a problem with using it as a cleaning method though residue does need to be considered.
As for landings and such; landings can present problems for some on position GTAW. Other than that I see no problem. In many shops I have been associated with stone saw pipe feather edges were welded to fittings with landings all day long and with less than 1% reject rate.
In other words, you need to make an adjustment but not a big one.

By Superflux (****)

Date 06-19-2014 13:45

Zcat,

As others have said, the blasting is an excellent prep, but NOT the final stage before fitting up for welding.
Supervision needs to be made aware of the noncompliance to the WPS stating that grinding and other methods after the blasting must be followed.
As for bevel prep, are you the only one welding these? Are there other welders involved in this that prefer to have a land on their bevels?
But if the procedure says a 0-1/32 bevel face, you really don't have a leg to stand on by the strictest interpretation if there is a 1/32 land.

FWIW, Blasting is totally a cool method to remove the rust, paint etc. as it can get down into the pores.
It still needs to (should) be followed up by grinding or sanding discs for GTAW work.

By FixaLinc (****)

Date 06-23-2014 00:12

Blasting of any kind leaves a residue. Anyone painting knows you can't just paint over blasted metal it has to be cleaned and prepped first. Same for welding it's leaving a residue coating you can't always see but it's there.

By Superflux (****)

Date 06-19-2014 19:33

Since I am the one that mentioned the "evil" word pore...
pore 1 |pôr|
noun
a minute opening in a surface...

Hmmm, I must have somehow implied that steel was porous and with the aid of a strong enough helper, one might be able wring out all that water that has soaked up in the iron.

By js55

Date 06-19-2014 20:37

Super,
Steel can be porous I suppose if something is small enough.
For example steel is 'porous' to X-ray and gamma radiation. Otherwise radiography would be useless to us.

By 803056

Date 06-19-2014 22:34

We have vacancies in the atomic lattice, we have atoms occupying a volume of space in the atomic lattice call the home position, but there aint no damn pores in sound metal. If there is, it is porosity and it is considered to be a discontinuity. If the porosity exceeds the acceptance limits, it is termed a defect.

Hey, wait a minute. Back the buggy up! Am I contradicting myself?

We can manufacturer molecular sieves using powdered metals. The powdered metal particles are selected and compressed to the proper degree to produce holes of the proper size. I guess one could call that product porous. Porosity with a purpose!

All that aside, I don't believe the porosity that was referenced by the previous post has nothing to do with this particular discussion.

Best regards - Al

By kcd616

Date 06-20-2014 06:57 Edited 06-20-2014 06:59

Al
well put
thank you
sincerely,
Kent
btw, I am glad my little woman coupons, because being on this forum I need lots of bandages and sometimes a pillow for my chair :eek:

By ZCat

Date 06-20-2014 09:33

I never said it was a 1/32" land, I'm talking about a factory bevel on fittings up to 24". It can be on up to about a 3/16" land and they just blast it and fit it. This is the most welder unfriendly big fab shop I've ever worked in. They're clueless. It's all about the production factor to them, they don't care what the welders want.

By 803056

Date 06-20-2014 09:53

I feel your pain ZCat. As I said, there is no cure for stupid.

Al

By js55

Date 06-20-2014 12:02

Oh guys come on!!!!!
Big landings are not that hard.
I've worked (welding and engineering) in fab shops that never touched the landings. And this even with a landing on one side with fittings and feather edges on the other with abrasive cut pipe. And still maintained less than a 1% reject rate. Especially on roll outs when we ran on top at over 200 amps and slightly on the downhill side. But even in position work as well.
I was never a phenom welder either. I was average. Though fast and efficient.

By 803056

Date 06-20-2014 12:21

It all depends on the acceptance criteria being applied.

There are sound welds as defined by API 1104 and there are sound welds as defined by B31.3 for high pressure service. Apples and oranges.

1% reject rate is relative. 1% to one standard is the same as 25% reject rate to a different welding standard. Even you have to admit not all welding standards are created equal.

Al

By js55

Date 06-20-2014 13:40

Al,
I don't understand the 1% 25% point.
Relative perhaps due to diameter, but not without strict limitation.
You shoot or scan 100 welds, one busts, its 1%. We do it the same for ASME, API, or AWS. Eazy peezy.
I can see where this would vary if you were volumetrically examining long seam welds on 40 foot pipe, or long fillets on manufactured columns and beams, where you might judge based upon a linear inch method to be more representative. But we don't manufacture pipe and we don't volumetrically examine fillets very often (once I remember on PV stiffeners). And even if we did I would resist the linear inch method unless they were really long welds. We do up to 42" pipe quite commonly (and even much bigger-we've done as large as 108"-still counts as one) that's over 120" of weld. Counts the same as a 2" weld. Doing this way homogenizes the numbers.
Relative perhaps. But I don't think this an accurate way of saying it. To go from 1% to 25% implies going form a linear method to a joint method. And Vice Versa. I can see going from the joint method to linear method could get you from 25% to 1%. Sounds like cheating but if your program is consistent and your customers know how you measure it its just as legit.
Having said all this 1% or less is superb by anybody's standards, especially utilizing the joint method. And we are proud of it.

By js55

Date 06-20-2014 13:43

Al,
And yes, I agree that not all standards are created equal. But any dealing with pipe that I have been involved in either explicitly or implicitly impose the joint method.

By 803056

Date 06-20-2014 13:45

So, your are saying the acceptance criteria of one piping code is the same as an other? Seriously?

Al

By js55

Date 06-20-2014 14:17

Al,
Of course not. I'm saying it doesn't matter that much. The numbers are meant to measure a level of quality within a Code/Standard context. If API is more lenient on say, IP, than ASME, so what? You compare API to API and ASME to ASME. A contractor who has a rash of IP can't jump to 1104 so his numbers go from 25% to 1% . If he is going to go from 25% to 1% he has to do it in the API or ASME context. And so the measuring standard is valid.
If a fabricator is operating with a variety of Codes and Standards (as we do) the numbers will homogenize over time and the measuring standard is still valid.
Your critique seems to imply there is something artificial or dishonest about the whole thing. While there is a certain arbitrariness in the establishment of the rules for all Codes and Standards, as long as everyone is playing by the same rules the system is valid, viable, and not without considerable accuracy.

By CWI7611 (**)

Date 06-20-2014 15:02 Edited 06-20-2014 15:05

I love this forum, yes js I said Love again. We have gone from sandblasting weld end preps to reject percentages. This comment isn't directed at anyone in particular, just adding fuel to the conversations.

I will say that sandblasting or any type of blasting creates a surface profile and this may have been what was meant when the term "pore" was used. This surface profile can contain some small particles of dust from the blasting process and thus be incorporated into the weld. Probably grinding or sanding (know what you are "sanding" with) is the better way to go. I think we can all agree with that.

Reject Percentage: If I have a 100 inch single pass weld length and I have a 1 inch defect is that a 100% failure or a 1% failure? What if I have a four pass 100 inch weld with a 1 inch defect. Is that 100 % reject rate or .25% reject rate. See what I mean. It all depends on how you calculate your statistics. I have heard of contractors that have figured the reject percentage based on weld length and number of passes. In some instances you could have every weld fail and if you figure it on pass length and number of passes you could have a respectable failure percentage. See, if you figure this "reject rate" correctly you can look as good or as bad as you want to.

By js55

Date 06-20-2014 15:39

CWI,
Those are valid points. And it certainly depends upon the integrity of the contractor as to whether it is legit or shenanigans. I have a tendency to think that those who take advantage of such methods are generally of the shenanigan category. But not necessarily so. They could simply believe they are utilizing the best method for their application.
And it is up to the customer to evaluate perspective suppliers and verify that they are considering apples to apples. It is only relative, as Al states, if you are comparing apples to oranges (especially the manipulative variety), but not inherently so.

As I said, if we ran a 108" diameter circumferential multipass weld (over 300 inches of weld) and had a few spots of porosity as a reject, its a 100% reject. No shenanigans. If our reject rate climbs, we fix it, we don't hide it.

Now, having said all this I would certainly be interested in someone relating which standards are lenient towards such shenanigans. API is not. ASME is not. At least not without really contorting the language and intent of the Code/Standard. An AWS D1X is essentially a VT Code wherein this type of thing is seldom applied (though I have no experience with D1.5).

By 803056

Date 06-20-2014 15:32

I make a distinction between codes knowing that comparing one standard to another is comparing apples to oranges.

A contractor that is fabricating girders that are subject to stringent radiographic acceptance criteria is not playing on the same ball field as a contractor constructing small building that are subject to VT and rarely subject to RT (if ever). A 1% defect rating for the bridge fabricator is very impressive, while the building fabricator, not so much.

The same is true in piping. A contractor that is fabricating to B31.8 and rarely needs to RT the piping is going to claim to have a very low reject rate. Meanwhile, the contractor fabricating and installing piping to B31.3 high pressure fluid service may experience a higher reject rate, but the welds are held to a higher standard. Apples to oranges.

This is where I find it interesting that Section IX's acceptance criteria for VT to be a "hoot." A welder that meets Section IX visual criteria may not be capable of meeting the requirements of the applicable construction code. Granted, with enough grinding and contouring nearly any weld can be made to "pass" the code. I've been involved in a few situations where it would be easier to put lipstick on a pig and sell it as Cameron Diaz than to get some welds to pass the VT requirements, never mind RT. Ultimately, the contractor claimed a high pass rate, but conveniently overlooked the number of "repairs" needed to pass.

The bottom line is that I wait to hear what welding standard the contractor is welding to before I say, "Wow, I'm impressed!"

So, when someone says their welders have a 1% reject rate, I withhold my applause until I know what construction code they are working to and whether volumetric NDT is required. I compare it to graduating from a university with a degree in the arts versus a degree in science. While the degrees may cost the same, I am not overly impressed with the degree in fine arts. Apples to oranges.

I am reminded of the project where a mechanical contractor was awarded a contract to install some piping. When I arrived on the job to qualify the welders I discovered they were required to do orbital welding on a piping system for pharmaceuticals. The stainless tubing was polished and passivated. At the time the contractor, the project management team, and the Owner simply assumed it was "just pipe." I explained to them that the project specification did not call out a construction code for the system they were installing. In the absence of a construction code there were no requirements for the contractor to meet. "First class workmanship" as stated in the project specifications does not tie the contractor to any specific requirements. At a project meeting the Owner described what they wanted. I told the assembly that what they were describing was the ASME BPE code. The system was not "just an other piping job." I told them that the contractor that had the award was not in a position to meet the stringent requirements of BPE. I told them the best thing they could do is let the contractor out of the contract and rewrite the project specification to include BPE as the construction code. The work is specialized and it required a contractor that had the experience and the proper equipment to do the job properly. They all agreed that my suggestion made sense. The contractor thanked me for getting him out of the contract. The contractor was prepared to deliver the apples, but he was not able to deliver the oranges.

Best regards - Al

By js55

Date 06-20-2014 16:00

Al,
A couple things.
I do not agree with what you say of B31.8. First of all percentages do not work the way you state. You may shoot fewer welds but when you bust they have greater significance to the overall numbers. You cannot hide a high real reject rate in low percentage sampling. This is true even within B31.3 when you go from a 5% to a 100% standard. It will all eventually homogenize. This is actually the basis of sampling philosophy.

Second, You argue great concern for VT in Section IX. I do not necessarily disagree with your concerns, however, this to me is still a bit odd, since Section IX requires either destructive or volumetric examination (destructive absolutely for short circuiting) as the primary criteria.
Now, I might attribute this to D1.1 thinking (not an insult) wherein so much emphasis is placed on VT. You are not required to perform volumetric in D1.1 AT ALL unless its cyclic service with the weld transverse to the stresses. D1.1 has this huge section devoted to volumetric examination and it is imposed from one single itty bitty paragraph hidden in the design section. That's a lot of faith in VT. Though having said this I would be glad to turn my own argument against myself and say, if its problematic, where's the failures to prove it.

By IowaCWI (*)

Date 06-20-2014 23:41

Js

I'm trying to see both sides of this debate. I think all Al is trying to say is that, if welder 1 is welding to a code that accepts porosity big enough to throw a cat through. And welder 2 is welding to a code that accepts no porosity, wouldn't it be safe to say welder 1 can claim a lower reject rate? I would have a hard time saying he is wrong about that. I guess I am not fully understanding your position on the subject.

By 46.00

Date 06-21-2014 00:07

......and what exactly has all this discussion, entertaining as it is, have to do with the OP's original question?

By 46.00

Date 06-21-2014 00:14

ZCat, If the WPS says the prep needs grinding or whatever, then that's what is needed, Sand Blasting is not acceptable! From experience, not thats that worth a dime, GTAW over sand blasted material is always a nightmare. The parent material needs to be ground back to clean steel!

By kcd616

Date 06-21-2014 07:21

Glyn,
thank you
my thoughts and experience also
with any metal
sincerely,
Kent

By 46.00

Date 06-21-2014 10:58

welcome Kent!

It aint rocket science after all, just common sense, which aint so common!

By js55

Date 06-23-2014 12:11

Iowa,
My position is that I am not disagreeing with Al. He is absolutely correct. What I am saying is that jumping from one Code to another doesn't matter. Reject rates are intended to be a measure within a giving Code application. The differing acceptance criteria, though certainly arbitrary to some degree still has its base in the service intended.
In essence, who cares what welders claim from Code to Code as long as everyone is playing by the same rules. Its the cheaters and those perpetrating shenanigans that are problematic not Coded variances.
Its a simple enough thing when evaluating a fabricator to determine if the bulk of their work is sewer service or high pressure steam.

By 803056

Date 06-21-2014 01:55

I enjoy these discussions. They make us think outside our comfort zones once in a while.

As for VT, even some of the ASME pipe codes will permit on-going (continuous) VT as a substitute for volumetric examination. Evidently, ASME sees some value in a thorough visual examination of the weld if it includes a material check, fit-up, root bead, intermediate layers, and a final.

By the way, you must be doing something right with 99% of your welds meeting the requirements of the code and project specifications. Now if you could only lower reject rate by another 50% ............

Best regards - Al :grin:

By js55

Date 06-23-2014 12:21

Al,
I enjoy them very much as well.

And I would certainly like to take some credit, but the truth is, these guys I work with were very very good before I came along. We constantly work towards perfection but unless you really slow down production you hit a wall. We have to make money to stay alive so you have diminishing returns on all efforts to improve.

And I would never say VT is not without value. As I posted earlier, given D1.1's requirement for essentially exclusive VT I can turn my oft quoted failure argument against myself and argue that it seems to be working very well.