Heat Treating of 800 Series High Nickle Alloys

[CFDFEAGURU]

Hello all,

In the design of heat exchangers and pressure vessels with the ASME (American Society of Mechanical Engineers) code, if certain materials are used above or at a certain temperature they must be heat treated after welding. This is know as PWHT (Post Weld Heat Treating) Also, if a pipe or tube is bent to too small a radius then heat treating is required. In this sense it is called PFHT (Post Form Heat Treating) However, the heat up rate is not defined by the ASME Section VIII Div. 1 code. There is a small section in the ASME Section III Nuclear code but it is very general. Lastly, the manufacturer of the material doesn't specify a heat rate either due to liability issues.

Anyways, if you are using UNS N08800 series (800, 800H, and 800HT) high nickel alloys at or above 1000 F they must be heat treated after welding. In a heat exchanger, the tube bundle can cause problems because the tubes can bow and bend under the thermal expansion of the heat treating, therefore, a properly supported tube bundle and a low enough but economical heat up rate is desired. Local heat treating is not very economical so it is desired to put the whole bundle in the furnace when it will fit and heat treat it all at once.

I have searched the internet and haven't found any trustworthy information on heat up rates of high nickle alloys. Do any of you know of any information on this?

Ironically, when these heat exchangers are in service they basically heat treat themselves but in order to have a stamped vessel the rules must be followed.

Thanks
Matt

 

[minger]

Have you by any chance checked the API standards?

 

[FredGarvin]

AMS-H-6875 states:

Rate of heating: Heating rates shall be controlled to prevent damage to the material (see 6.2). Pre-
heating at 1000 °F-1200 °F is recommended before heating material above 1300 °F if the material:
(a) Has been previously hardened above Rc 35, or is made of steel of 0.50 (nominal) percent
carbon or over, or
(b) Has abrupt changes of section, or sharp re-entrant angles, or
(c) Has been finish machined.

I can't find anything pertaining to just nickel based alloys though. I'll keep looking.

 

[CFDFEAGURU]

Minger,

Have you by any chance checked the API standards?

I did check the API standards that I have. I only have three of them but the numbers are escaping me. Anyways, didn't find anything.

Fred,

AMS-H-6875

What standard is that?

Thanks
Matt

 

[FredGarvin]

Fred,

What standard is that?

It's about as generic a spec you can have for steel heat treatment. It gets referenced by many, many other heat treat specs.

http://www.sae.org/technical/standards/AMSH6875A

 

[Astronuc]

AMS = Aerospace Material Specifications, which are developed by SAE (Society of Automotive Engineers).

By 1916 the Society of Automobile Engineers membership had grown to 1,800. At the annual meeting that year representatives from the American Society of Aeronautic Engineers, the Society of Tractor Engineers, as well as representatives from the power boating industry made a pitch to SAE for oversight of technical standards in their industries. Aeronautics was a fledgling industry at that time, and few could have been expected to know the essential role it would take in world history in a very short time. Early supporters of the concept of a society to represent aeronautical engineers were Thomas Edison, Glenn Curtiss, Glenn Martin, and Orville Wright.

Out of that fateful meeting in 1916 came a new organization with new horizons. This was to be a new society representing engineers in all types of mobility-related professions. SAE member Elmer Sperry actually created the term "automotive" from Greek autos (self), and Latin motivus (of motion) origins to represent any form of self powered vehicle. The Society of Automobile Engineers became the Society of Automotive Engineers, and the most important chapter in the SAE saga was underway.

. . . .

http://www.sae.org/about/general/history/

There are also similar (and mostly redundant) standards within ASTM.

The applicable ASTM standards for Incoloy 800HT (UNS N08811) are: B163, B366, B407, B408, B409, and one would want the one for tubing - B408 - ASTM B407 - 08a Standard Specification for Nickel-Iron-Chromium Alloy Seamless Pipe and Tube.

Now one must realize that the SAE/ASTM specifications are sufficiently broad because this allows manufacturers to produce material that while it might be not optimal, they don't have to reject the material (which is costly). If one buys any alloy, one is responsible for understanding the behavior in the alloy and products intended environment, and one should, if at all possible, impose tighter specifications.

Under QA/QC programs, particularly nuclear programs, suppliers are required to collect and retain furnace heat treatment charts to assure that the material complies with the appropriate specification. This information may be considered proprietary, but the customer can execute a nondisclosure agreement and by virtue of a purchase agreement (contract) obtain access to the heat treat charts. One might have to pay extra for this type of agreement, and certainly one will have to pay for tighter specs. I should have B407 and others at my office, so I'll see if that has a heatup/cooldown rate.

The ASTM spec doesn't necessarily have requirements on welding however. It's simply a spec for bulk material production. It doesn't go into how the material (tube, sheet, strip) is processed in subsequent manufacture or how it is used in commercial operation.

 

[FredGarvin]

The ASTM spec doesn't necessarily have requirements on welding however. It's simply a spec for bulk material production. It doesn't go into how the material (tube, sheet, strip) is processed in subsequent manufacture or how it is used in commercial operation.

Most specifications I have worked to call out AWS specs to cover weld integrity and inspection criteria.

 

[Astronuc]

Most specifications I have worked to call out AWS specs to cover weld integrity and inspection criteria.

Yes - aerospace and aeronautic companies refer to SAE/AMS specs. Some ASTM specs are effectively identical and redundant. There has been some historical rivalry between SAE and ASTM, which I still don't understand, but it seems to come down to personality conflicts and turf. AWS welding specs are referenced by aerospace and nuclear suppliers and users.

I looked at B407, Standard Specification for Nickel-Iron-Chromium Alloy Seamless Pipe and Tube, which includes Incoloy 800, 810 and 811. It covers the finished tube, not what happens afterward, and it does not address a heatup or cooldown rates. Any mechanical treatment, e.g., bending, and subsquent welding is not addressed in this spec. It might be in a ASME code.

Normally subsequent processing involves a proprietary process, which must meet certain QC/QA and technical requirements. It is up to the purchaser to put requirements in the purchase order or contract, and that should include a right to audit the process (subject to appropriate nondisclosure agreements). How a material is processed will have a profound affect on its mechanical and corrosion performance.

 

[CFDFEAGURU]

Thanks everyone for your help on this.

Astronuc, the ASME doesn't specify the heatup or cool down rates. ASME simply states the rates have to be agreed upon between the fabricator/heat treator and the end user.

The ASME Section III has a Non-Mandatory appendix D that specifies preheat temperatures for the welding.

I have a method that my superior developed, it is in my office, so I will post it Friday.

Thanks
Matt