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ahmednabi
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Weld Joint Strength Reduction Factor (W) in ASME B31.3

01/09/2015 1:20 AM

I attended a training on Process piping last week and I came across this weld joint strength reduction factor (W) in the thickness calculation formula. What is the physical significance of this factor? how is it different then weld joint efficiency factor E?
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Tornado
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#1

Re: Weld joint strength reduction factor (W) in ASME B31.3

01/09/2015 3:15 AM

Can you give us some more context, such as what numbers for W are allowed under what conditions? This does sound similar to how E is used in pressure vessel calculations, but I don't if piping is the same.

Sorry I don't have a full answer, but this may lead you in a good direction.

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ahmednabi
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#2
In reply to #1

Re: Weld joint strength reduction factor (W) in ASME B31.3

01/09/2015 4:57 AM

As per ASME B31.3 para 302.3.5(e) 2006 Revision, W is taken as 1 for metals under service temperature of 510 degree C and 0.5 for 815 degree C. Between these two temperatures linear interpolation is used. This value of W is then used in calculation of required thickness of pipe wall.

t= PD/(SEW+PY)

where E is joint efficiency and Y is a factor dependent on temperature and material (calculated from table, usually taken as 0.4)

My question is we are already using E for joint efficiency why to further increase the thickness further by W? Wouldn't it be too conservative?

Also note that this factor is absent in 2002 edition of B31.3 and adopted in 2006 I guess.

P.S: Thank you for your welcome note :)
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Whitephone
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#4
In reply to #2

Re: Weld joint strength reduction factor (W) in ASME B31.3

01/09/2015 12:44 PM

The weld joint strength reductionfactor is the ratio of the nominal stress to causefailure of the weld joint to that of the base material forthe same duration. Except as provided in (f) below, theweld joint strength reduction factor, W, shall be in accordancewith Table 302.3.5.
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Crabtree
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#3

Re: Weld Joint Strength Reduction Factor (W) in ASME B31.3

01/09/2015 12:32 PM

Substances get weaker with rising temperatures. So in order to contain the same pressure at elevated temperature, there has to be more substance to couner the lower strength.

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Whitephone
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#5

Re: Weld Joint Strength Reduction Factor (W) in ASME B31.3

01/09/2015 12:50 PM

What about Creep test to determine W

http://www.wmtr.com/en.whatisacreepTest.html
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Whitephone
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#6
In reply to #5

Re: Weld Joint Strength Reduction Factor (W) in ASME B31.3

01/09/2015 1:05 PM

WP

ASME B31.3 edition 2010

Appendix V

Larson- Miller parameter

Rupture life

Creep rupture

Example in point V304 is clear .
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ahmednabi
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#7

Re: Weld Joint Strength Reduction Factor (W) in ASME B31.3

01/09/2015 2:46 PM

Thankyou all of you for valuable answers. I am quite clear now about the difference between weld joint efficiency and weld joint reduction factor. here is what i understand

Weld joint efficiency E is a factor which incorporates any deficiency in the joints due to joint structural weaknesses like weld cracks or internal pores which reduces the overall structural stregth hence extra thickness is added.

Weld strength reduction factor incorporates the reduction in strength due to creep phenomenon at elevated temperature
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