8/5/2015 ASME Impact Test Requirement

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ASME Impact Test RequirementThe ASME Impact Test Requirement article provides you with informationabout impact test requirements in pressure vessel design and construction.

Let's say, you have a pressure vessel underdesign, process and construction has not startedyet.

Based on the ASME impact test requirement,you need to make assessment to see that eitheryour pressure vessel is exempted from impacttesting, or you need to carry out the test.

There are 4 steps for impact test exemption assessment. You need to knowthese steps. You might be exempted in the first, second or third steps andmight not be exempted even in step 4.

So if you are in step 4 and you have not exempted, then you need to carryout the test. I will explain the process for exemption in this article.

Basic Concept:

You may know carbon steels and low alloy steels exhibit a drastic change intheir room temperature ductility at subzero service temperatures. Differenttypes of materials exhibit different types of transition behavior.

We can see there is a sudden, phenomenal drop in their notchtoughnessproperties below the "transition" range of temperature, which should be amatter of concern for us.

Body centered cubic or Ferritic alloys exhibit a significant transition inbehavior when impact tested over a range of temperatures. Above transitiontemperature range, impact specimens fracture in a "ductile" manner,absorbing relatively large amounts of energy.

At lower temperatures, i.e. below thetransition temperature range, the impacttest specimens are found to fracture in abrittle (cleavage) manner, absorbing lessenergy.

And within the transition temperature range,the fracture is a mixture of ductile and brittle

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nature.

A material would be invulnerable to a sudden drop in notchtoughness at thelowest specified service (or design) temperature, if it is proved by conductingCharpy Vnotch Impact tests on representative test samples, at reference(the lowest service) temperature.

Grain refined carbon steel forgings and wrought materials (thoroughlyworked and normalized) generally exhibit good notch toughness.

ASME Code Section VIII Div 1 exemption rules for ASME Impact TestRequirement:

There are specific rules in ASME Code for exemption from ASME ImpactTest Requirement. This test is very expensive, so pressure vesselmanufacturers are trying to be exempted for this costly test.

You need to follow the following clauses to make exemption assessment forASME impact test requirement:

UG20(f) →→→UCS66(a) →→→ UCS66(b) →→→UCS68(c)

First you have to keep your pressure vessel design data available and thenrefer to UG20 (f). If you are exempted from this clause, you do not needproceed further.

But if you are not exempted by UG20 (f), you have to proceed to UCS66(a), but again if you are exempted, there is no need for more assessment.

But if not, you have to proceed to UCS66(b). If you are exempted now,there is no need for more assessment; otherwise, you have to proceed toUCS68(c), and again if you are still not exempted, you have to carry outimpact testing.

For some cases, You might be exempted from the ASME impact testrequirement in the first stage in UG20 (f). In others, You might be exemptedin UCS66(a) or UCS66(b) or UCS68(c). If you are not exempted, you mustprepare yourself for doing this costly test.

This test would be more costly out of the US because of LaboratoryAccreditation requirements. Also, there are fewer accredited labs in Europeand the Middle East, and their price is high as well.

UG20(f)

We will start with UG20(f) for the ASME impact test requirement. If yourMOC (Material of Construction) is categorized in PNo. 1 or 2 (Refer toASME Code Section IX for PNo Definition) and your MOC thickness has thelimited value defined in this clause, then you might be exempted from impacttesting.

But you need to refer to Fig UCS66 in ASME Code Section VIII Div 1 andsee in which A, B, C or D curves your MOC is listed. All ASME carbon steeland low alloy steel material is distributed in these 4 groups (Curves) ofmaterials.

You need to know that the materials listed in curve D have the besttoughness property, better than the materials listed in curve C. Similarlymaterials listed in curve C have better toughness properties compared to

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8/5/2015 ASME Impact Test Requirement

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materials listed in curve B and materials listed in Curve B have bettertoughness than materials listed in Curve A .

See Following Fig UCS66(a):

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When you determine your MOC curve, then you have to review UG20(f)and look for the possibility of exemption from the ASME impact testrequirement. There are some other conditions in this clause, which youshould consider for exemption.

For instance, the vessel should be hydrostatically tested after completion,and the thermal and mechanical loading can not be a design controllingfactor.

For example, if your MOC is a normalized SA 516 Gr.70 with 0.75 inchthickness you will be exempted from ASME impact test requirement.

Your thickness, in this example, is 0.75 of an inch, and is listed in curve Dwhich is up to 1 inch, you are exempted by this clause. Of course, you willbe carry out hydrostatic test and ensure that the mentioned loadings are nota design controlling factor in your considered pressure vessel.

UCS66(a)

So assume that in the above example, your MOC thickness is 1.125 inchinstead of 1 inch, you will not be exempted by UG20(f) and you have torefer to UCS66(a);

But for assessment, based on this clause, you need to know your pressurevessel MDMT (Minimum Design Metal Temperature). Assume that is 20degree F, so you should now go to Fig. UCS66 and locate 1.125 inch in thehorizontal axis and draw a vertical line.

In a similar way, locate 20 degree F in the vertical axes and draw ahorizontal line. These two lines will cross each other.

See above Figure, the lines are identified in red.

If the cross point falls above the curve D (because your MOC is listed in

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curve D) you are exempted. Otherwise you are not, but for the currentexample, you are above the curve D so you are exempted from impacttesting.

To simplify your assessment for the ASME impact test requirement, the Fig66 has been converted to the table(table UCS66). For any MOC withspecific thickness you can go to this table and see what is the minimumpermissible temperature without impact testing.

See following UCS66(a) Table:

In the above example (normalized SA 516 Gr.70, Curve D, 1.125 inchthickness), the minimum permissible temperature without impact test is 26degree F. This means that, if in the above example your MDMT changesfrom 20 degree F to 27 degree F, then you cannot be exempted from theASME impact test requirement by UCS66(a), and you have to proceed toUCS66(b)

UCS66(b)

Let us explain this clause with the above example. Your MDMT from aboveis 27 degree F, nominal thickness is 1.125 inch, normalized SA 516 Gr.70listed in curve D and you are not exempted by UCS66(a)

So you are here to continue your assessment to find a chance forexemption. You have to refer to Fig UCS66.1 and calculate the followingformula:

Ratio= tr E / (tn –c)

tr is the required design thickness for all applicable loading. We assume forthe above example that is 0.95 inch. E is your joint efficiency, and weassume for this vessel it is 1. This means your vessel is RT2, tn is yournominal thinness, which in the example from above it is 1.125 inches, and Cis corrosion allowance, and we assume it is 0.125 inches; so let calculate:

Ratio = 0.95x1/(1.125 – 0.125) Ratio= 0.95

See following Fig UCS66(b):

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Then go to the Figure UCS66(b) and in the vertical axes locate Ratio anddraw a horizontal line. Then locate the cross point with the graph and draw avertical line to cross the horizontal axis.

You will be able to reach a value of 8 in the horizontal axes. This 8, is your 8degree F bonus from table UCS66, which you can reduce by 8 degrees Fminimum permissible temperature in table without impact testing.

In the above example, your MDMT is 27 degree F, and in the UCS 66 table,the minimum permissible temperature without impact testing designated 26degree F. So with this clause you can reduce it to 36 degree F(26 8 = 34).Your MDMT is 27 degree F, so you are exempted from impact testing withthis clause.

UCS68(c)

Let us change one variable in the above example. Let's assume you need tohave 45 degree F for your MDMT. Other variable are the same; it meansnormalized SA 516 Gr.70 listed in curve D, thickness 1.125, so you can seeyou are not exempted by UCS66(b);

This is because the minimum permissible temperature is 36 degree F, butyour MDMT is 45 degree F, so UCS68(c) might be helpful.

It says that if post weld heat treatment is not a code requirement and your PNo is 1 and you carry out post weld heat treatment, a 30 degree F bonus willbe granted to you to reduce the minimum permissible temperature in tableUCS66.

So when post weld heat treatment is code requirement?

It is code requirement when your service is lethal and when your thicknessfor PNo. 1 is greater than 1.5 inch;

So, for our example, our service is not lethal and our PNo. is 1 andthickness is 1.125 and it is less than 1.5 inch: therefore, post weld heattreatment is not code requirement.

It means if you carry out post heat treatment, a 30 degree F bonus will begranted by this clause. For this example our minimum permissibletemperature would be 3630=66 degree F, and your MDMT is 45 degree

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F, so you are exempted from impact testing.

Now the worst case: in the above, assume you need to have 70 degree Ffor your MDMT; you can see with this new condition you cannot beexempted even by UCS68(c) and you have to carry out impact testing.

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19 Comments Sort by

Azhar Yusuf ·Mechanical Engineering at Ocean Rubber Factory LLC

100 likesLike · Reply · Jul 22, 2015 10:46pm

Phani Sridhar Ch ·National Institute of Technology Trichy

excellent explanation and interpretationLike · Reply · Mar 13, 2015 10:24pm

Gogulakrishnan Appunni ·Regional Engineering College

impact test requirementsLike · Reply · Jan 23, 2015 2:13am

Mauricio Radtke ·Universidad de Concepción

Thanks a lotLike · Reply · Sep 20, 2014 6:53am

John McqueenStraight to the point and very informative

Like · Reply · 1 · Feb 26, 2014 1:35pm

Monzur Abu Emon ·Marine Academy, Chittagong

Could you please address PQR, welding consumables, andproduction impact test requirement as well? Very good writeup indeed. Thanks.Like · Reply · Feb 22, 2014 11:29am

Jingsong HUVery good article for new pressure vessel engineer.Like · Reply · Feb 14, 2014 1:26pm

Chung Youngyin ·Geoje

Thank you so much for good and detail explanation.Like · Reply · Dec 27, 2013 1:21am

Bipin Singh ·Dubai, United Arab Emirates

Really very good by example ,

Like · Reply · 1 · Dec 13, 2013 2:30am

Faizur Rahman ·Gmam inter college

realy vry nice 1... itsvery easy to understnd, thks alot.....

Like · Reply · 1 · Sep 24, 2013 5:17am

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