Low stress stamping: Definition

[vesselguy]

Hi all,
This is something I never thought much of until I casually talked about material identificaiton stamping with one of our Inspector. We always specify low stress stamping when we ask the fabricator to stamp the material identification or some location marking on a vessel or exchanger. But what exactly is low stress stamping?

The way most of us commonly define Low stress stamping is when a letter is formed by the use of a blunt tip (reads as round tip) continuous or intermittently dotted die stamp. That sounds great because it is obvious that a round indentation makes lower stress than a "V" shaped indentation. However, what is the "offiical" definition of low stress? Less than 0.1x Yield stress (as an example)? At what radius of the indenter will it be "high stress"?

Any thought on this? Know of any Code such as API or ASTM that defines these parameters?

 

[arto]

McMaster's list's "gentle mark" steel stamps on pg 1793:

http://www.mcmaster.com/

"Solid-face stamps meet ANSI specification IN45, 2.2A39 for low-stress impressions."

"Dotted-face stamps produce even lower stress impressions than the solid-face stamps. Nuclear grade, they meet Nuclear American Society of Mechanical Engineers Code Section 3, Div. 1, Paragraph NA-3766.6 (2)."

 

[arto]

p.s. MIL-STD-792 lists tip radii etc. for Low Stress Die Stamps