A106 Gr.B & A105 LT15

[GMN_]

I was reviewing a vessel drawing the other day and noticed that the nozzle necks and flanges were to A106-B LT15 and A105 LT15 respectively. As per table A1-M of ASME B31.3 the standard A106-B and A105 are suitable down to -29degC. My query is why have these been specified as LT15? Is it simply that they have been impact tested as part of the material requisition?

 

[XL83NL]

First of all, what does LT15 mean? Second, is B31.3 your design code? B31.3 has options to use a lower MDMT by reducing the stress, review para 323.2.2.

 

[GMN_]

The query is what does the LT15 mean??

The design code is technically PD 5500 as it is a pressure vessel, however I am a piping engineer and given these are piping components I figured this may be the best place to get an answer.

I am currently undertaking a PD 5500 Annex D assessment on an existing vessel and don't have access to material certs for this particular vessel. I know that from ASME B31.3, these materials are suitable, however I have never seen A106-B and A105 labelled as LT15 before. When looking at older BS material specifications they are labelled LTXX when they have been impact tested at -XXdegC. I was just wondering if this was the same methodology??

 

[Ehzin]

I've never seen that naming convention before but if that format shows up in your companies documents (Not sure what BS means unless your using that in the traditional sense) then I suppose I'd work with that. I would avoid referring to B31.3 for questions related to a vessel. If constructed to Section VIII, I would refer to that code and it's related materials tables.

Thanks,
Ehzin

 

[weldstan]

ASME Section VIII, Div. 1 limits these grade to -29C based on thickness. As thickness increases,empact testing must be done at the MDMT temperature or lower. Sew the material groups (A,B,C,D) curves in UCS-66. The materials may have been impact tested at -15F or -15 C.

 

[DVWE]

Typically in the piping industry LT means "Low Temp", but that is a slang term, and it never refers to A105 or A106 materials. Something like A333 pipe is sometimes referred to as "Low Temp" pipe, in fact, even the ASTM/ASME title of that document has the term low temperature in it.

Just a possibility, and with what weldstan has posted, it could be your answer.

 

[GD2]

GMN,
There are couple of things to look at why the impact testing was done:
1. -29C is good only upto a pipe wall thk up to 12.5mm for A106 gr B pipe. As WT increases. Minimum temp will increase too. For example.if the pipe WT is 25mm. Minimum temp for the pipe will be 0C (zero C).
2. A105 is good upto -29C. It is not dependent on thickness.
3. Even if these two materials can stand upto -29C, impact testing is not required by the material manufacturing standard.
4. Now.this minimum temp set by the code is different than MDMT(Minimum Design Metal Temp). MDMT is set by the process design conditions.
5. For a given WT. If the MDMT is above the min temp.impact testing of the base metal (pipe) is not required.If MDMT is below the minimum temp, impact testing is required.
6. The first part of the rule (MDMT>or= min temp. Donot limit the Owners to do a impact testing. It gives the Owners a more confidence level.

To find the reason why the designer chose to impact test the materials, you need to find out the following data:
A) The MDMT
B) the pipe WT

You said while 'reviewing vessel drawings...'. Is your vessel made of a pipe? Usually. Vessels are made out of plate material.A106 is a pipe designation.A105 is a forged material and widely used for flange.










Ganga D. Deka, P. Eng
Canada