NACE MR0175-Carbon Steel: PWHT Issues. Some of them are: a) Based the requirement of UW-2 (a) when our service is lethal and our material is carbon steel or low alloy steel. B) Based the requirement of UW-2 (c) when our pressure vessel is unfired steam boiler and our material is carbon steel or low alloy steel.
by Murali
(UAE)
(UAE)
What are PWHT requirements in pressure vessel inspections?
Bob's Reply: I prefer to answer to this question in two separate questions as below:
1. When and where PWHT is mandatory by code requirement?
2. How PWHT must be done when it is mandatory?
Pressure Vessel Inspections-Answer to question 1:
If we focus only in ASME Code Section 8 Div 1, there are lots of conditions which cause the PWHT to be mandatory. Some of them are:
a) Based the requirement of UW-2(a) when our service is lethal and our material is carbon steel or low alloy steel.
b) Based the requirement of UW-2(c) when our pressure vessel is unfired steam boiler and our material is carbon steel or low alloy steel.
c) Based the requirement of UW-2(d) when our pressure vessel is subjected to direct firing and our material is carbon steel or low alloy steel.
d) Based the requirement of UCS-56 when our nominal thickness exceeds a specific value, for instance 38 mm for P No.1 material or 0 mm for P No.3 material.
UCS-56 also gives min. PWHT temperature and min. holding time (soaking period) based on P-Nos. and thickness respectively.
e) Similarly to the UCS-56, the same apply for other martial groups i.e. UNF-56, UHA-32, UHT-56 and etc.
f) Based the requirement of UCS-68(b) when our MDMT (Minimum Design Metal Temperature) is below -55 Degree F.
Pressure Vessel Inspections-Answer to question 2:
When one of above requirement applies to us, then we must do PHWT based the requirement of UW-40 which detail to us the PHWT procedure.
Some important requirements in this clause are:
a) For Furnace PWHT, Loading Temperature shall not exceed 800°F, heating rate 400 deg F/hr/inch of thickness, cooling rate 500°F /hr/inch of thickness.
Still air cooling permitted below 800°F. During soaking period, temp difference between hottest and coldest part shall not exceed 150°F.
b) Minimum overlap for PWHT in multiple heats is 5 ft.
Bob's Reply: I prefer to answer to this question in two separate questions as below:
1. When and where PWHT is mandatory by code requirement?
2. How PWHT must be done when it is mandatory?
Pressure Vessel Inspections-Answer to question 1:
If we focus only in ASME Code Section 8 Div 1, there are lots of conditions which cause the PWHT to be mandatory. Some of them are:
a) Based the requirement of UW-2(a) when our service is lethal and our material is carbon steel or low alloy steel.
b) Based the requirement of UW-2(c) when our pressure vessel is unfired steam boiler and our material is carbon steel or low alloy steel.
c) Based the requirement of UW-2(d) when our pressure vessel is subjected to direct firing and our material is carbon steel or low alloy steel.
d) Based the requirement of UCS-56 when our nominal thickness exceeds a specific value, for instance 38 mm for P No.1 material or 0 mm for P No.3 material.
UCS-56 also gives min. PWHT temperature and min. holding time (soaking period) based on P-Nos. and thickness respectively.
e) Similarly to the UCS-56, the same apply for other martial groups i.e. UNF-56, UHA-32, UHT-56 and etc.
f) Based the requirement of UCS-68(b) when our MDMT (Minimum Design Metal Temperature) is below -55 Degree F.
Pressure Vessel Inspections-Answer to question 2:
When one of above requirement applies to us, then we must do PHWT based the requirement of UW-40 which detail to us the PHWT procedure.
Some important requirements in this clause are:
a) For Furnace PWHT, Loading Temperature shall not exceed 800°F, heating rate 400 deg F/hr/inch of thickness, cooling rate 500°F /hr/inch of thickness.
Still air cooling permitted below 800°F. During soaking period, temp difference between hottest and coldest part shall not exceed 150°F.
b) Minimum overlap for PWHT in multiple heats is 5 ft.
On Tue, Sep 1, 2015 at 12:02 PM, Raghuram Bathula <[email protected]> wrote:
PWHT is exempted for all thicknesses and weld types of P-No 1 base material, subjected to meeting the requirements of Notes in Table 331.1.3 (such as preheat and multiple layer welds...).
On 1 September 2015 at 12:24, S.Mohammed <[email protected]> wrote:
Dear all,
When Pwht Is Required For Carbon Steel Welding
As old ASME B31.3-2012 we know it was above 19mm req pwht,
![Steel Steel](/uploads/1/1/9/4/119493048/400103085.jpeg)
now i read ASME B31.3-2014,little confused me with pwht exemption and pwht requirements and control thickenss 331.1.3?
q1- what is thik req for pwht for P1 as per b31.3 2014 ?
q2 : for P1,mentioned more than 25mm thk and 95C preheat exemption from pwht so less than 25mm not require pwht ?
mohd.
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When Pwht Is Required For Carbon Steel Conductivity
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