Help understanding Section 2 Part D 1

[mengnr]

We are designing a part and trying to clarify for our suppliers and vendors what parts are allowable under Section 2 Part D. I have read the intro, and don't see any explanation about when the temper and thickness given in the charts apply. Is this the temper and thickness of the raw material or the finished part? If we are machining a vessel roughly a 7" cube with 1" thick walls out of a single piece of material and then welding a flange on, is the thickness based on the wall thickness of the part (1") or the thickness of the material used to make it (~8")? And does it have to be one of the allowable tempers before any processing, after machining or after welding? Thanks.

 

[metengr]

It is the temper and thickness of the material used prior to fabrication of the pressure retaining item or connections.

Thermal treatments after welding are followed by construction rules in the applicable code book section.

 

[mengnr]

Thanks for the clarification. Can you tell me the reasoning for requiring a certain temper from the raw material rather than just the part after its in service?

 

[metengr]

Two reasons; first one is in some cases you may have designs that utilize only bolted or threaded connections with no welding during fabrication. Thus, no thermal treatments are performed after final fabrication of the component.

Second, after final fabrication is completed and welding was performed OR you decide to subject the finished component to final heat treatment after welding to achieve actual strength properties makes no sense either because of distortion to the component.

This is why material should be procured with final heat treatment or at least formed and heat treated before final fabrication.

 

[trottiey]

I disagree with metengr. The temper in Section II must represent the material in service because the material properties will apply in service. If the raw material had a different temper, then the vessel manufacturer must comply with UG-93(b) when heat treating the part to meet Section II Part D. (That's if you're using Section VIII Div. 1. Other sections probably have similar clauses.) Distortion should be considered, but the decision to buy raw material in the final heat treatment or heat treat later is usually a commercial one based on availability.

As to thickness, I think that would be the thickness of the raw material. It's the original forming processes that impact material properties the most. For example, SA-240 S31254 1/4" thick has lower strength than 1/8" thick, but you can't improve the material strength just by machining it down; it's the rolling that matters.

Now that's just for the materials. Post-weld heat treatments are a different beast altogether, controlled by testing coupons that are exposed to the same thermal history as the real part.

 

[metengr]

I don't believe there is any disagreement. All you have stated is that heat treatment can be done by a manufacturer after final fabrication to ensure mechanical properties are met in accordance with Section II, Part D. I said this in my second post...

This is why material should be procured with final heat treatment or at least formed and heat treated before final fabrication.

 

[davefitz]

A related problem just occurred with a valve outlet diffuser, specified as SA387 F91. The diffuser was a dished plate, and the foundry that fordged the plate into a dish only performed a 1650 F anneal during hot work ,and did not perform a final N+T at 1900+ F. Their claim is that the wording of SA387 specifically applies only to the original plate prior to hot work.

Of course, a final N+T is required with this alloy, as the anneal at 1650 F for 3 hrs is an example of overtempering for this alloy. But their response now raises a concern regarding every F91 piece form that foundry and every F91 valve from that valve company.

 

[metengr]

Sounds like some poor Purchaser had no clue on what they were buying, which is typical today, and is placing balme on the supplier (LOL).

The mill is absolutely correct in their interpretation, SA 387 is a plate specification and what you do with the plate after it is supplied from the mill or foundry in accordance with the heat treatment requirement below is the Purchaser's problem.

Grade 91 plates shall be normalized at 1900
to 1975°F [1040 to 1080°C] and shall be tempered at 1350
to 1470°F [730 to 800°C].



Seems straightforward to me....

 

[davefitz]

meteng:

Well, almost. The purchase specification had included the requirement for a final N+T following all F91 hot work, but such a requirement either was not forwarded by the valve vendor to the foundry that supplied the outlet diffuser ( dished plate), or it was not read by the foundry. Of greater concern is that the valve mfr believes the part does not require a final N+T, regardless of the material breach of contract and regardless of the metallurgical neccesity, as it is not a "pressure part" subject to ASME code.

We are aware that several bypass valve outlet diffusers had failed afer a few years service at some Florida CC plants ( valves by another vendor ), and now we have a clue as to why such a short life can be expected.

 

[vesselfab]

we purchase a heck of a lot of thick SA-516-70 plate from mill in as rolled condition, by code it must be normalized.

We normalize ourselves and save substantial money.

what we do is buy the plate as rolled, but have the MTR done on coupons that are normalized at mill, then normalize ourselves to the same procedure as mill.

Just like head manufacturers do. Normalize in conjunction with hot forming.

 

[trottiey]

If you're building to ASME code, you need to follow the SA-387 heat treatment after forging, not just on the plate from the mill. Assuming this is a Section VIII Div 1 part, UF-31 is clear: "After all forging is completed, each vessel or forged part fabricated without welding shall be heat treated in accordance with the applicable material specification."

But the valve manufacturer might have a case when they say the ASME code doesn't apply. There is nothing wrong with building a valve that doesn't meet code, and many don't. It's local regulations and system design that determines which things have to meet code or not, which code, and what section. Does this valve have a code stamp on it? Did the purchaser ask for a valve that meets code?