RE: [MW:24171] RE: 24163] Material properties

Please think about where you are on a stress strain curve.

 

Elasticity is the ability of the material to stretch and return to its original length. You can regard the steel as being elastic up to its yield stress. [I am sure someone will add to this but I want to explain in simple terms].

 

The elongation is a measure of plasticity or ductility (not elasticity) – how much it will stretch and flow before it breaks when stretched beyond the elastic limit. The elongation figure is the total level of elongation [measured over the standard gauge length] on the tensile test specimen at failure – measured after it breaks.

 

Bolts are used at a stress below the yield stress (or 0.2% proof stress) [Check what is meant by the 0.2% proof stress if this is not clear to you] – i.e. they work at stresses within the range where they are elastic. The corresponding level of strain to the yield stress (i.e. the x-axis value on the stress strain curve) is about 0.5%. Compare that with the elongation to failure figure of 16% which you mention as being the specification minimum to understand the difference – scale out 0.5 cm against 16 cm to get the measure of the difference.

 

A high yield stress and high UTS does not correlate with a high figure of elongation to fracture.

 

In specifications a minimum figure of elasticity is stated and a high figure of ductility is good because it means there is a high margin between when the steel yields and when it breaks – as could occur in the case of accidental overload. There is no maximum figure stated in specifications for components working in the elastic range because it is simply unimportant – this is the case in the case of bolts and most engineering components.

 

You to ask for clarification with respect to national and international standards – but you already have that when you state 'SA-193, as per standard elongation % should be min 16% but test certificate shows 20%'.

The standard states a minimum value. Your tests have met that minimum value. There is no maximum value. You have met the requirement of the specification.

 

Best wishes

 

Alan Denney

AKD Materials Consulting Ltd

 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Karthi Shanmugananthan
Sent: 23 January 2016 12:54
To: materials-welding@googlegroups.com
Subject: Re: [MW:24169] RE: 24163] Material properties

 

Dear sir

Since UT & YS also found higher side, so I felt elasticity properties of material may higher and it may create problem during service conditions. .... regarding this I need clarification with reference to national /international standards

Regards
S.karthikeyan

On Jan 23, 2016 6:15 PM, "'Bijay' via Materials & Welding" <materials-welding@googlegroups.com> wrote:

Dear, 

As per TC the elongation is min 16% and you got 20% then you should accept it.

Sent from Yahoo Mail on Android

 

On Sat, 23 Jan, 2016 at 6:01 pm, Karthikeyan Shanmugananthan

<skkn133@gmail.com> wrote:

Dear sir
Thanks for ur response,recently myself reviewed a test reports of bolts as per SA-193, as per standard elongation % should be min 16% but test certificate shows 20% whether can I accept material or not. All bolts are pertaining to pressure vessel application.
Also suggest, maximum limit of elongation %

Regards
S.karthikeyan

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