Weld Overlay

What your WPS and PQR says about that.

We are using a combination of WPs in the the joint , i.e For weld joint welding(without clad) doin it with 7018 and after that using a diff WPS for weld overlay.

thats wht creatin the confusion at the point , do i need to do the PWHT before overlay or not ?

Further more as per our past experience , we have found that IF we do the PWHT after the weld overlay , we usually find the CRACKs in RT which after grindin turns out to be located near the DIffuion lin ( i.e 309lmo barrier layer)

Any suggestion would be welcome from your side

Thnaks

There are two different conditions as per ASME sec VIII and ASME Sec. IX. As per sec VIII div 1, table UCS 56, note 2 (c)(5), weld overlay PWHT is not mendatory. as below:

TABLE UCS-56

POSTWELD HEAT TREATMENT REQUIREMENTS FOR CARBON AND

LOW ALLOY STEELS

Minimum Holding Time at Normal Temperature

Normal Holding for Nominal Thickness [See UW-40(f)]

Temperature,

Material °F, Minimum Up to 2 in. Over 2 in. to 5 in. Over 5 in.

P-No. 1 1100 1 hr/in., 2 hr plus 15 min 2 hr plus 15 min

Gr. Nos. 1, 2, 3 15 min for each addi- for each addiminimum

tional inch over tional inch over

2 in. 2 in.

Gr. No. 4 NA None None None

NOTES:

(1) When it is impractical to postweld heat treat at the temperature specified in this Table, it is permissible to carry out the postweld heat

treatment at lower temperatures for longer periods of time in accordance with Table UCS-56.1.

(2) Postweld heat treatment is mandatory under the following conditions:

(a) for welded joints over 11⁄2 in. nominal thickness

(b) for welded joints over 11⁄4 in. nominal thickness through 11⁄2 in. nominal thickness unless preheat is applied at a minimum temperature

of 200°F during welding

(c) for welded joints of all thicknesses if required by UW-2, except postweld heat treatment is not mandatory under the conditions specified below:

(1) for groove welds not over 1⁄2 in. size and fillet welds with a throat not over 1⁄2 in. that attach nozzle connections that have a finished inside diameter not greater than 2 in., provided the connections do not form ligaments that require an increase in shell or head thickness, and preheat to a minimum temperature of 200°F is applied;

(2) for groove welds not over 1⁄2 in. in size or fillet welds with a throat thickness of 1⁄2 in. or less that attach tubes to a tubesheet when the tube diameter does not exceed 2 in. A preheat of 200°F must be applied when the carbon content of the tubesheet exceeds 0.22%.

(3) for groove welds not over 1⁄2 in. in size or fillet welds with a throat thickness of 1⁄2 in. or less used for attaching nonpressure parts to pressure parts provided preheat to a minimum temperature of 200°F is applied when the thickness of the pressure part exceeds 11⁄4 in.;

(4) for studs welded to pressure parts provided preheat to a minimum temperature of 200°F is applied when the thickness of the pressure part exceeds 11⁄4 in.;

(5) for corrosion resistant weld metal overly cladding or for welds attaching corrosion resistant applied lining (see UCL-34) provided, preheat to a minimum temperature of 200°F is maintained during application of the first layer when the thickness of the pressure part exceeds 11⁄4 in

But if you see ASME Sec IX QW253/4/5/6.1 and QW 407.6, PWHT of corrosion resistant overlay is neccessary.

My suggestion is you should carry out weld joint PWHT in full compliance and use low carbon version of electrodes for overlay with proper pre heat and interpass temperature and post weld heat up to 300°C for one hour shall give you good results.

Thanks 4 your advice, but my issue is it fine to do the PWHT i.e. stress releiving / normalizing of the claded / overlay joint (SA 516 GR 70 - 50 THK + SA240 T316L - 4 MM).

What about the the sensitization of the SS part ?

Im asking this as we have found cracks all over the Weld near the fusion line of the overlay only after normalizing