From time to time, questions are asked regarding painting or coating of a pressure vessel or even a pressure retaining item prior to hydrotesting.
I was forwarded this interesting article that was published in Materials Evaluation, September, 1993. The article is titled " Don't Paint Before Hydrostatic Testing" and is authored by Jon Batey.
To summarize, the author explains how the various construction codes and in-service repair codes like the NBIC are either silent or briefly mention caution on the issue of painting or coating before hydrostatic testing.
Several tests were actually conducted on a 4" Schedule 40 carbon steel pipe that was internally pressurized with specific hold times at 1100 (30 min), 2000 (10 min) and 2400 psig (5 min). The pressure was increased in 100 psig increments. The various coating systems that were evaluated consisted of;
- vinyl finish over inorganic zinc primer
- vinyl finish over vinyl primer
- epoxy finish or epoxy primer
The pipe section was pre-dilled with twelve, small diameter thru holes (0.0135" and 0.020") to simulate weld or fabrication defects.
The results of the pressure tests revealed some interesting results;
- in a test pressure range of 325 psi to 1125 psi, the vinyl coating systems failed. At the onset of failure, the vinyl coating locally disbonded into a blister that ruptured.
- the epoxy system adhered and did not disbond even at 2425 psig pressure.
So, you may want to think twice during fabrication of pressure retaining items to coat after hydrostatic testing to make it easier for your AI.
Hi,Thanks a lot, i search in ASME B31.3 below bold sentence,but i couldn't find,can u please help me for this.,where it is exactly so that i can decline this deviation.Please help me if possible uregently because my PM pressuring me to reply that will be appreciated.Waiting for reply.Regards,SatishOn Thu, Sep 30, 2010 at 1:33 PM, Bathula Raghuram (Mumbai - PIPING) <R.Bathula@ticb.com> wrote:
Interesting, and you have a valid point but nothing is proven, until then just go with the flow (tried and tested methods). No Inspector would be happy but bound to accept as per code. remember your company specification prohibits it and you are intended to accept, hence code reference is given, Masking of any discontinuity by thin layer of paint, may be yes perhaps may be not. If you refer the paragraphs of these codes which will give a cautionary statement at the end "painting/coating may mask the leak".
Normally weld joints are left open and rest of the area is painted before hydro.
In my opinion 105 bar is too high for a layer of paint to with stand, or you may allow only blasting and priming before hydro and final coating after hydro. If I remember correctly only Australian code AS1210 prohibits it.
From: Satish Hingalkar [mailto:shingalkar@gmail.com]
Sent: Thursday, September 30, 2010 12:49 PM
To: Bathula Raghuram (Mumbai - PIPING)
Subject: Re: [MW:7283] Can we do painting prior to hydrotest?
Hi,
Thanks for prompt reply
Piping system of having pipe rack near about 4 KM,service-Nitrogen,Code ASME B31.3
As u said,ASME B 31.3 allows,but my query is that whether painting will affect the joint leak detection normally found in hydrotest??
As per my knowledge,Painting has ability to penetrate and plug/ seal off small pin holes which are normally detected in hydro test. After curing, paint can withstand pressure in small pin holes that can obstruct the leaks. But during operation, paint can be decomposed and start leaking,please comment.
Regards,
Satish
On Thu, Sep 30, 2010 at 7:27 AM, Bathula Raghuram (Mumbai - PIPING) <R.Bathula@ticb.com> wrote:
You have not specified the type of component, fluid and design code.
ASME code for both vessels and piping have this provision. Sec VIII div 1 allows except for lethal service (UG 99) and B31.3 allows except for sensitive leak testing (345.3.1)
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Satish Hingalkar
Sent: Wednesday, September 29, 2010 11:55 PM
To: Materials & Welding
Subject: [MW:7276] Can we do painting prior to hydrotest?Dear Members,
Our contractor has raised a design change request for painting prior to hydrotest.As per COMPANY specification,painting to be carried out after successfull complection of hydrotest,but contractor wants to do painting before hydrotest,can we accept this deviation? if we want to accept the deviation,what criteria to be follow??
Our design conditions are 105 barg hydrotest pressure and design temp.85 deg.c,NDT is 10% MT & 10% RT.
Waiting for reply.Pl.respond ASAP.
Regards,
Satish
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