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How to avoid PWHT

How to avoid PWHT

Postby aliattari » Thu May 30, 2013 6:14 am

We are planning to weld SS pipes , max thickness 50mm with CS temporary blindflanges / end caps for the hydrotest purpose. I want to ask that can I use a WPS without PWHT for THK above 19 mm. Since these welds are temporary , & will not be subject to service stresses and process fluids. After hydro test , these will be cut out.
What will be the possible solution to avoid PWHT for such temporay dissimilar welds?
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Re: How to avoid PWHT

Postby wgadmin » Thu May 30, 2013 7:54 am

If the WPS that you intend to use had originally been qualified by a PQR without PWHT as well as this PQR covers the actual welding variables (thicknesses, base materials, filler metals, positions, preheat, etc) then you can use this WPS. Instead, if the WPS had originally been qualified by a PQR with PWHT, then you shall perform PWHT since the deletion of PWHT may affect the notch-toughness properties of the weldment making it vulnerable to brittle-fracture during the hydro test and thus an accident could happen injuring the nearby personnel and/or causing damage to the nearby equipment.

If you are to take the risk to avoid the PWHT, then you have to take measures to reduce the possibility of welding failure during the hydro test. First of all you have to avoid partial penetration weld since it happens to produce stress concentration points as well as to avoid any other weld practise that generates such vulnerabilities to the weld. Moreover you shall do surface and volumetric NDTs as efficiently as possible (at your case PT and UT may be the most appropriate) preferably after at least 48 hours of the welding completion in order to detect possible hydrogen crack. Additionally I would recommend you perform preheat since it helps to avoid hydrogen cracking and also I suggest you avoid rapid cooling of the weld as it hardens the weldment and the HAZ (post weld hydrogen release may be beneficial). Above all you shall take additional measures to assure the safety of the personnel and of the equipment in case of weld failure during the hydro test.
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Re: How to avoid PWHT

Postby Logosweld » Mon May 26, 2014 3:13 pm

wgadmin wrote:If the WPS that you intend to use had originally been qualified by a PQR without PWHT as well as this PQR covers the actual welding variables (thicknesses, base materials, filler metals, positions, preheat, etc) then you can use this WPS. Instead, if the WPS had originally been qualified by a PQR with PWHT, then you shall perform PWHT since the deletion of PWHT may affect the notch-toughness properties of the weldment making it vulnerable to brittle-fracture during the hydro test and thus an accident could happen injuring the nearby personnel and/or causing damage to the nearby equipment.

If you are to take the risk to avoid the PWHT, then you have to take measures to reduce the possibility of welding failure during the hydro test. First of all you have to avoid partial penetration weld since it happens to produce stress concentration points as well as to avoid any other weld practise that generates such vulnerabilities to the weld. Moreover you shall do surface and volumetric NDTs as efficiently as possible (at your case PT and UT may be the most appropriate) preferably after at least 48 hours of the welding completion in order to detect possible hydrogen crack. Additionally I would recommend you perform preheat since it helps to avoid hydrogen cracking and also I suggest you avoid rapid cooling of the weld as it hardens the weldment and the HAZ (post weld hydrogen release may be beneficial). Above all you shall take additional measures to assure the safety of the personnel and of the equipment in case of weld failure during the hydro test.

good reply with good explanation
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