HF Acid Service

[rickylee]

1) Does ASME Section VIII Div 1 have requirements depending on the type of process fluid or gas?

2) Specifically, does a fitting designed for HF acid require PWHT?

Thanks, Rick

 

[metengr]

1). ASME Section VIII, Div 1 does make specific reference to lethal service requirements in Part UG - fluid or gas.

2). The answer to your question depends strictly on material of the nozzle, not service conditions

 

[MJCronin]

ricklee...

I think that it might be important here to review what the varoius ASME pressure vessel and piping codes are....and what they are not.

These codes and standards will:

- Enable the design, inspection, fabrication and testing of pressure retaining components.

- Enable the sizing and selection of pressure relief devices

- Specifically ban and sometimes restrict, certain types of materials, designs, constructions and methods of attachment and fabrication

- Provide rules for inspection and service life evaluation after the code-designed components/systems have been placed in service

These codes and standards will NOT:

- Guide the designer/specifyer in the selection of design pressures, temperatures, or loading conditions.

- Guide the designer/specifyer in the selection of coatings or metal finishes or the design of any internal, (non-pressure retaining) structure or feature

- Guide the designer/specifyer in the configuration, volume or shape of the pressure component or system

- Provide guidance in the evaluation and selection of pressure component support types or analysis proceedures

These are only a few of the limitations/restriction that come to mind

My opinion only


MJC

 

[TomEun]

1. ASME Section VIII, Div.1 & B31.3 Requirements for Lethal Service

The ASME Section VIII, Div.1 does not specially call out services which are defined as lethal. This is the responsibility of vessel user-process engineer.

UW-2(a) ; Butt welded joints in vessels to contain lethal substances shall be fully radio-graphed. When fabricated of carbon or low alloy steel shall be post weld heat treated. The joints of various categories shall conform to paragraph UW-2.
UCS-6(b)(1); Steel plates conforming to specifications SA-36, SA-283 shall not be used for pressure parts in pressure vessels..

The definition of lethal service and grouping of the materials are normally addressed in local regulations, such as federal, state, province, and country. Table 1 shows a group of chemicals which are listed as Class A poisons by the Code of US Federal Regulations, Title 49.

Table 1 Class A Poisons
Bromoacetone
Chlorpicrin
Cyanogen
Ethyldichlorarsine
Hydrogen Cyanide
Methyldichlorarsine
Mustard Gas
Nitric Oxide
Nitrogen Dioxide
Nitrogen Peroxide
Nitrogen Tetroxide
Phosgene

These materials in their pure state (100% conc.) would undoubtedly be considered lethal by the Code. For these materials in solution with other non lethal components, however, the process engineer must make a judgement as to the minimum concentration of the lethal component in solution above which the solution would be considered lethal with regard to Code rules.

Meanwhile ASME B31.3 defines the toxic (lethal) service in Categoy M Fluid Service. (See Table 1.1.8.2 and Fig.1.1.8.1)

2. Company Specifications

Even though HF acid is not listed in Table 1, many companies require the PWHT for the facilities to prevent hydrogen blistering, hydrogen embrittlement and SCC in HF acid service. Please find “NACE publ. 5A-171 Receiving, Handling, and Storing HF acid”.(hardness requirements)

Thomas Eun
thomaseun@shaw.ca

 

[MJCronin]

Tom,

There is no one source of information on what chemicals in which concentrations constitute "lethal service" under the ASME code definition.....the whole situation is a big mess, made worse by owners relying on confused pressure vessel designers to tell them if the pressure vessel should be designated that way.....

How about this list of chemicals ? Are they all to be stored in "lethal service" designed vessels ?

http://www.cdc.gov/niosh/idlh/intridl4.html

Other discussions are contained in:

http://www.eng-tips.com/viewthread.cfm?qid=130393&page=2

Others have argued with me, but I stronly feel that there is too much subjectivity in this designation...

My opinion only

MJC

 

[grampi1]

Always PWHT in HF!

 

[stanweld]

My experience with HF Alky Units has been to always PWHT the carbon steel vessels.