Skip to main content

Re: [MW:35723] PWHT after Hydro

By Materials & Welding
 For main pressure welds on materials like P11, P91, and LTCS, PWHT is essential when prescribed, and the integrity test (hydro) 
must follow all heat treatments unless the code or a client-specific deviation allows. The code does not permit skipping a repeat hydro. 
The logic is that since PWHT can alter the microstructure and relieve stresses, it might reveal or create discontinuities that could 
compromise pressure integrity—meaning a follow-up hydro is generally required.

For P11 (1.25Cr-0.5Mo)
PWHT is mandatory for most thicknesses per ASME.
PWHT after the hydro test is typically acceptable, if permitted by project specs.
For P91 (9Cr-1Mo-V):
Highly sensitive to heat treatment cycles.
Incorrect PWHT can alter microstructure and reduce creep strength.
Often, clients require a hydro test after PWHT, especially in critical service.
LTCS:
Generally, more lenient.
PWHT after hydro test may be acceptable depending on the joint type ,thickness, and low temp. impact.

According to ASME B31.3, Clause 345.4.2, PWHT after hydro testing is allowed, and a repeat hydro test is NOT required if:

The system has not been opened or altered after the hydro test.

PWHT does not weaken or alter the pressure-retaining capacity of the system.

The PWHT is part of the planned fabrication sequence, and the test pressure already applied exceeds the pressure that the 

system would experience at the elevated PWHT temperature.

However, some client specifications override this and may demand a re-hydrotest after PWHT, especially for P91, which is 

sensitive to microstructural changes. PWHT is not required at all for LTCS unless impact testing is required at a low temperature.

C Sridhar.

  


On Thu, 17 Jul 2025 at 16:10, Kannayeram Gnanapandithan <kgpandithan@gmail.com> wrote:
Dears
     Materials P11,P91 & LTCS.
  Is there any provision to perform PWHT after Hydrotest without having to repeat the Hydrotest again ?

THANKS & BEST REGARDS,
KG.PANDITHAN, BE, IWE,  CSWIP 3.1,
ISO 9712 Level 2 in VT,
ASNT-Level II in PT,MT,RT & UT,
LA ISO 9001-2015, ISO 3834, EN 15085, 
International Welding Engineer. 
CONSULTANT-WELDING & QUALITY
Mobile no: +919940739349

--
https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/materials-welding/CAJzm4eO6c%2BFD26ucwQX--8gxLfqTEqT0Q168jPUb2xS%3DcPipqg%40mail.gmail.com.

--
https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/materials-welding/CAHo%3DYiiqNbmdb-4UQVr8QofPZ1XwX%2B9%2BVfkDTE9mu4qVgpQDQg%40mail.gmail.com.

Comments

Post a Comment

Popular posts from this blog

Heat tint (temper) colours on stainless steel surfaces heated in air // Heat tint

By Materials & Welding
Introduction The colour formed when stainless steel is heated, either in a furnace application or in the heat affected zone of welds, is dependent on several factors that are related to the oxidation resistance of the steel. The heat tint or temper colour formed is caused by the progressive thickening of the surface oxide layer and so, as temperature is increased, the colours change.   Oxidation resistance of stainless steels However, there are several factors that affect the degree of colour change and so there is no a single table of colour and temperature that represents all cases. The colours formed can only be used as an indication of the temperature to which the steel has been heated. Factors affecting the heat tint colours formed Steel composition The chromium content is the most important single factor affecting oxidation resistance. The higher the chromium, the more heat resistant the steel and so the development of the heat tint colou...
Post a Comment
Read more

Materails FAQs

By Materials & Welding
Q: What are equivalents for standard Q 235 B (and Q 235 A) for U-channels? (asked by: boris.vielhaber@vait.com) A: DIN Nr. = 2393 T.2, 2394 T.2, EN 10025 W. Nr. DIN 17007 = 1.0038 Design DIN 17006 = RSt 37-2, S235JRG2 (Fe 360 B) Q: What is St DIN 2391 BK material? (asked by: dmcandrews@automaticstamp.com) A: Precision steel tubes, cold-finished/hard. Q: What is C.D.W. Boiler Tube? (asked by: montydude123@yahoo.com) A: Cold Drawn Welded Boiler Tube. Q: WHAT IS W.Nr. 1.4301? PLS TELL US IN EASY LANGUAGUE (asked...
21 comments
Read more

The Schaeffler and Delong diagrams for predicting ferrite levels in austenitic stainless steel welds

By Materials & Welding
Introduction Ferrite is important in avoiding hot cracking in during cooling from welding of austenitic stainless steels. 'Constitution diagrams' are used to predict ferrite levels from the composition by comparing the effects of austenite and ferrite stabilising elements. The Schaeffler and Delong diagrams are the original methods of predicting the phase balances in austenitic stainless steel welds. Nickel and chromium equivalents A 'nickel equivalent' is calculated for the austenite stabilising elements and a 'chromium equivalent' ferrite stabilising elements. These are used as the axes for the diagrams, which show the compositional equivalent areas where the phases austenite, ferrite, martensite (and mixtures of these) should be present. Although intended to show the phase balance of weld fillers, these diagrams can also be used to illustrate the phase balance of the 'parent' material. There are different diagrams for dif...
Post a Comment
Read more