[MW:9206] HEAT EXCHANGE ACCIDENT

Dear all,

 

My company has an EPCC (Engineering, Procurement, Construction and Commissioning) contract for an Ammonia plant with a contractor. During the transportation a shell and tube heat exchanger is faced to an accident which causes a severe damage on its shell side. Major defect has the size of 50 x 50 CM and bighted inside approx. 4 cm (like a bowel but not so smooth).

Repair procedure submitted by the contractor is divided in two sections as follows:

 

: Section 1

1-      Performing the hydrostatic test on shell and tube side.

2-      Performing the MT and UT on dented areas.

3-      Performing the hardness test on all damaged joints (base metal, weld metal and HAZ).

4-      If the mentioned test on this section is approved then heat exchanger is ready for shipment to site

 

 

: section 2

     If the mentioned test in section "A" do not approved then:

1- Damaged tubes shall be replaced.

2- Dented areas on shell shall be cut and patched with the same material.

3- Performing the UT and MT on new weld seams.

4- Performing the hydro-test on shell and tube side.

 

Specification of this heat exchanger is as follow:

·         Size: 1500 ID x 7900 L

·         Type: NEN horizontal

·         Code : ASME SEC viii DIV 1 & TEMA CLASS R

·         Shell and tube side design pressure: 180 barg

·         Shell side design temperature: 240 deg C

·         Tube side design temperature: 335 deg C

·         MDMT: -14 deg C

·         Shell and tube side are in H2 service

·         Shell material: SA-387-11 CL2+S5

·         Channel & tube-sheet material:SA-336-F11 CL2+S13

·         Tube material: SA-213T11

·         PWHT: already done after fabrication.

 

   My request from you:

a-      Please check the submitted procedure for its adequacy in detecting the possible damage/ and have your comment for new test if any.

b-      By my opinion in any case a window on shell side shall be cut to check the condition of heat exchanger tubes and renew the dented area.

c-      Since the heat exchanger is already PWH treated after the fabrication, please let me know your opinion regarding the second PWHT after repair and its effect on properties of base metal.

 

Thank you for your prompt attention,