direct welding of CS A333 to CS A106

[suraiya]

For some reasons, a small fabricator who has obtained job for some piping works with my company had run out of low temp CS A333 elbows. As an alternative , they proposed use of CS A106 elbows.
Can anyone tells me if it is okay to use elbows made of normal CS A106 materials , which will be welded to low temp CS A 333 pipe?

 

Hello,

It depends upon the minimum design temperature and how thick it is. See ASME/ANSI B31 Code for Pressure Piping, B31.3, Process Piping, Paragraph 323.2.2(b), Figure 323.2.2A, Table 323.2.2, and Appendix A - Table A-1.

Regards, John.

 

[KernOily]

As John said, as long as the MDMT and wall thicknesses are OK, the next step would be to get a new welding procedure, although since both of those are P1 metals, your existing procedure may cover you. I think if I was doing it I would still ask for a new procedure, PQRs, etc. Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com

 

[jepp]

Among other things that you may want to put in the new welding procedure, in this specific case, I'd like to suggest that you ask them to use welding electrode for CS A333 materials.

rgds,
jepp

 

[GGH]

If I make the assumption that your original design selected A333 with the additional costs (impact testing) that would be incurred over A106 it was because it was necessary. I would therefore be surpised if A106 would meet the design intent. If for some reason A106 is an acceptable substitute for A333 in this case I suggest you make this substitution clear in your records in case temperature re-rates are conducted at a later date.

 

[Teeboog]

GGH is correct. A106 Gr. B and A333 are one in the same. However,the difference is that A333 has been impact tested. I would not allow the substitution if you are operating a low temps.

 

[suraiya]

Thanx for all replies. I'm sorry that I don't make my case clear enough. In my case, the design temp range that we're looking at is -20C to 50C. However operation temp will be around 10C-15C. It is very unlikely that we'll go beyond this operational range.

 

[GGH]

suraiya,

I would not select materials that do not meet the design conditions. Imagine explaining to a court of law if there was a failure that you (not the designer) made a material substitution on the basis that failure was unlikely. Challenge the process designer, if the design temperature range is unduly conservative get it changed, make the whole system from A106 and save some cash.

 

[Seldom]

A subject near and dear to my heart and I agree wholeheartedly with GGH.

I've seen this scenario played out time and time again. The fabricator screws up and wants to take a short cut/substitution at the expense of the design specifications. If you decide to go with using the nonconforming fittings, where's your weakest link? The A106 fittings, that's where! Why waste your company's money specing out A333 for the system in the first place when just because of the fabricator's negligence and pressuring you, forces you to bastardize the system!

You mention:
"In my case, the design temp range that we're looking at is -20C to 50C. However operation temp will be around 10C-15C. It is very unlikely that we'll go beyond this operational range."

OK, you've pretty well got yourself talked into making a change but consider this before you give the go-ahead. Have you considered the possiblitity of a change in the service conditions of your system next month or next year, five years or ten years? You might say that it can't or won't happen. Wrong!!! Are you absolutely sure that if you allow the nonconforming fittings to be used, that the documentation will be adequate or even available for the next engineer? It's been my experience that it won't be there and the "road paved with best intentions" now, won't help him then either!

 

[TD2K]

I would first question why the initial low temperature specification was set at the -20C value if operation below 10C is 'very' unlikely. The margin between design and operating temperature on the low side seems excessive especially if it pushed the piping material to A333 from A106. Is there an autorefrigeration case that may have set the low temperature spec?

As others have suggested, if this isn't well documentated and discussed with the key players, there is more than enough chance later for finger pointing and expensive rework.

Personally, for some elbows, I'd tell the fabricator to install per specification. How they get them is their problem.

 

Tell the fabricator he can use the A106 if he first proves the material meets the minimum impact requirements required of the A333 originally specified.

 

[umamagesh]

On rme1's suggestion is like asking the fabricator to prove that monkey is man. Both material might look alike but not the same. A333 has good property for low temp impact as already explained. But your case of 10 deg is not low temp.
What if youy think of changing the whole to A106. I think A106 is ok for temp 10 deg. Also i agree that you have a big factor if you are suggesting -20 deg as design min. I strongly believe that over engineering is as dangerous as under engineering. Optimising is the best solution.
Any comments.