ASTM240 304L WPS for ASTM240 304 Material?

By Lawrence (*****)

Date 01-22-2015 12:52 Edited 01-22-2015 12:57

Wow, good question.

Oh... welcome to the Forum Jms !

This would be less of a burden if your procedures were pre-qualified. Then I would be a matter of generating a new WPS and yer done.

I think the difference in "groups" is attributable to the difference in carbon content and how that affects weld and base metal and post weld treatments.

Type 304L is an extra low-carbon variation of Type 304 a lower carbon content that eliminates carbide precipitation due to welding. Because of this it can be used in the ”as-welded“ condition, even in severe corrosive conditions. 304L often eliminates the necessity of annealing weldments except for applications specifying stress relief. It has slightly lower mechanical properties than Type 304.

I never noticed they were in different groups in Table 3.2 But here is your loop hole to explore sir !

I'm looking at a 2007 revision of D1.6 but if you look ever so closely... You will see 304 actually is listed in both groups (A & B)... See 3.2 continued with listings for Pipe, castings, fittings etc.

Now take a look at Table 3.2 footnote "a"
"Several alloy designations appear in both Base Metal Group A and Group B. The correct Base Metal Group for a given base metal depends on the ASTM Specification to which it was purchased."

So it may be that your MTR's (Material Test Reports, for those readers living in Rio Linda) give you the blessing already... If not, maybe explore some supply chain tweaks that provide what you want.

The rest is above my paygrade :)

Again, Welcome to the forum !

.

By Jms99300 Date 01-23-2015 09:04

Thanks for the response and the warm welcome to the forum Lawrence! At this point we were able to close some issues using the pre-qualification route, hopefully all will turn out to be so easy.

Thanks for the info, it all checks out with my understanding of the situation as it is. Our 304L product, the one we started with years ago, is made to be put in corrosive environments, thus the design requirement for low carbon material. For the ones that we can't pre-qualify according to D1.6 we're now looking at having to perform a series of necessary tests in order to prove that using a WPS for a mechanically 'weaker' material will not affect the functionality of the product calling for the 'stronger' 304. Any thoughts on that? From an engineering stand point I feel like its a bit of a joke, but for the quality aspect its a bit of a nightmare - this is for the nuclear industry as well, which amplifies that.

Regarding the loophole you mention - I had considered that before myself, but unfortunately, upon realizing that the foot note for superscript a) from table 3.2 says:

"Several alloy designations appear in both Base Metal Group A and Group B. The correct Base Metal Group for a given base metal depends upon the ASTM Specification to which it was purchased."

this becomes a dead end since I'm looking at both products using A240 specification.

By js55

Date 01-30-2015 19:44

First of all keep in mind that 304L is not necessarily a weaker material. It simply has a lower 'SPECIFIED' tensile strength requirement. The C content of 304 may be the EXACT same as that which is used in a 304L. And in fact, in many cases it is. They try and dual cert that stuff as much as possible, not to mention save money on alloying.
Also, the L is not necessarily related to its application in corrosive service as opposed to non L grades. It has to do with its tendency to sensitization. Stainless steels as a whole are intended predominantly for corrosive service. All of them.

By ssbn727 (*****)

Date 01-31-2015 01:05

Very well described and explained Js! That is so common with 304 SS pipe flanges having dual certs... Very well said indeed with regards to the sensitization tendency with respect to the L grades.

Respectfully,
Henry

By 803056

Date 01-31-2015 13:20 Edited 01-31-2015 13:22

JS, isn't the allowable stress for "L" grades of austenitic stainless steel lower at elevated temperatures per ASME construction codes? If I remember correctly, above temperatures of 350 degrees F or so, the allowable stress for the "L" grades is somewhat lower that that permitted for the non "L" grades. The highest allowable stress (at elevated) temperatures is assigned to the "H" grades of austenitic stainless steel. Hence the idea that the "L" are not as strong as the non "L" grades. The point missed by some people is that the difference in allowable stress is for applications where the service temperature is elevated.

Best regards - Al

By ssbn727 (*****)

Date 02-01-2015 00:28 Edited 02-01-2015 01:00

Isn't that what H sub-grades or variants of SS primarily used for - elevated temps? please let me elaborate further...

Within the usual designations of the common austenitic grades of stainless steel, such as 304 and 316, there are "sub-grades" - "L" and "H" variants - with particular applications...

The low carbon "L" grades are useful where welding or other high temperature exposure will occur, particularly welding of medium or heavy sections... The low carbon is one way of delaying or preventing grain boundary chromium carbide precipitation (often referred to as sensitization) which can result in intergranular corrosion in many corrosive service environments... As shown in the time temperature- sensitization curves below, the precipitation of carbides occurs over time at temperatures in the range of about 450-850°C... The time for damaging precipitation to occur is highly dependant upon the amount of carbon present in the steel, so low carbon content increases resistance to this problem... Because of their application area the "L" grades are most readily available in plate and pipe, but often also in round bar... In the absence of heavy section welding, or of high temperature exposure, the corrosion resistances of the standard and "L" grades are usually identical...

Composition limits for 304 and 304L are identical in all respects except for carbon content (304L does permit up to 12.0%Ni, compared to 10.5% max for 304 - but given the cost of nickel it is usual for both grades to have close to the minimum of 8.0%, so there is no practical difference)... Neither 304 nor 304L has a minimum carbon content specified... A carbon content of 0.02% therefore fully complies with both 304 and 304L specifications... The Tensile and Yield strengths for 304 are slightly higher than that of 304L...

"H" grades are the higher carbon versions of each of the standard grades... The high carbon results in increased strength of the steel, particularly at elevated temperatures (generally above about 500°C)... Both short term tensile strengths and long term "creep" strengths are higher for these high carbon grades... "H" grades are produced primarily in plate and pipe, but may be available in some other products... Applicable grades are most commonly 304H and 316H, but high carbon versions of 309, 310, 321 and 347 are also specified in ASTM A240/A240M... The specialist high temperature grade 253MA (S30815) has no low or standard carbon version at all. As discussed above, these high carbon content grades are susceptible to sensitization if held in the temperature range of about 450-850°C... If it occurs this will result in impaired aqueous corrosion resistance... In general however, this is not an issue for a steel that is primarily intended for high temperature strength... The grades that are “stabilized” by addition of titanium (321 or 316Ti) or niobium (347) do not suffer from sensitization even after exposure at 450 – 850°C because the Ti or Nb combines preferentially with the carbon... Even the high carbon versions (321H) resist sensitization...

The high carbon version of 304 is 304H... This has the same composition specification as standard 304 except that 304H does not have the 0.10% nitrogen maximum limit which applies to both standard and "L" grades and there is a slightly different chromium content range... In addition all austenitic "H" grades must have a grain size of ASTM No 7 or coarser...

The three grades 316, 316L and 316H are exact counterparts to the 304 series... Again only the carbon contents differentiate these grades (and the nitrogen and grain size limits mentioned above)... Compositions of the alternatives are therefore as in the following table (from ASTM A240/A240M-07; for full compositions refer to the standard)... Specifications for some other products, particularly tube and pipe, have a carbon limit of 0.035% or 0.040% maximum for 304L and 316L, but are otherwise the same as for flat rolled products...

In practice, steel mills generally ensure that the "L" grade heats meet the strength requirements of the standard grades, ie. 304L and 316L will almost always have yield / tensile properties above 205 / 515MPa, so will meet both standard and "L" grade requirements...

A note about Dual Certification: It is common practice for certain products including plate, pipe and some bar to be stocked as “dual certified”... Such product is certified by the manufacturer as fully compliant with both 304 and 304L or 316 and 316L... Thus it has the resistance to sensitization expected of an “L” grade plus the higher strength of a standard grade.... Dual certified products are generally precluded from use at high temperatures (over about 500°C) because of their low carbon content, the same as other “L” products... There is also a dual certified 321 / 321H, but there is no “L” version of 321...

There are many differences between the two variants, but in order to avoid posting up another of my famous walls of text, I'm going to stop here and see if anyone else has something to add here. :grin:

Respectfully,
Henry

By js55

Date 02-02-2015 21:45

Henry, Just to add, there is no L version of 321 because it is stabilized with Ti. Same as with 347 with Cb.

By 46.00

Date 02-14-2015 13:52

Not quite a wall of text!

By js55

Date 02-02-2015 19:54

Al,
Yes it is, exactly as you say. But again its specification thing, not a real material property thing. I was simply trying to clarify for the OP the difference in specs and real material properties. As a short hand way of saying it I have no problem with saying its 'weaker', so to speak. We all do short hand like that, myself included. I just thought it important to clarify.
And allowable stresses are an odd thing. You never really know how much data has gone into the numbers in the tables unless you're involved in its acceptance. But having said this I would guess that with a large enough sampling the carbon would overall be lower in L grades and therefore justify not only lower tensiles but lower allowables as well, though there would I think be considerable overlap.
And now I have rambled on too long.

By 803056

Date 02-10-2015 16:40 Edited 02-10-2015 16:43

Never, you always add insight to our understanding of code issues. I never skip your posts.

Sometimes I feel like we are cheerleaders for a specific few contributors, but there is a reason for it. Those contributors know what they are talking about and offer value to this forum. They deserve the recognition. You are one of those that deserves our recognition and our thanks for your contributions. That isn't intended to be a slight to other contributors (you know who you are), they also get their well deserved gold star now and again.

Best regards - Al

By js55

Date 02-13-2015 14:42

Al,
To receive such comments from someone that I have such tremendous respect for is a compliment of the highest order.
Someone once said something about standing on the shoulders of giants. I have been most fortunate in knowing a few giants.
But luck counts too.