Inspection Intervals for Check valves & Thermowells.

[Nabeel Ahmed Qureshi]

Thermowells & Checkvalves are present at every process plant. These items are thought as less critical & therefore lack due focus in terms of frequent inspections. Few days before at our site, one of the CV's flapper got disengaged from its lever (swing type CV) & got stucked in the line & ultimately plant was shutdown for one complete day to fix the issue. We are now setting inspection intervals for these items at our site. Can any body let us know the guidelines or reference of any code/standard/ best practices which governs the inspection frequencies of these items. Request to share your experience / site practice.
Regards
NAQ

[ben]

I would refer you to Sec. 7 of API 574 "Inspection Practices for Piping System Components".
Inspection interval is to be defined on the basis of following:
1. Consequence of a failure
2. Risk involved (likelihood of a failure)
3. Amount of corrosion allowance remaining
4. Historical data available
5. Regulatory requirements

This is mandatory that each process plant / facility must perform a complete study on their system to determine the right inspection frequency of piping components.

[Inspectengr]

You can also do the following as we practice:

1. High Pressure Loop thermowell to be inspected by DPT during every TA. (Currently we ensure 100% on Urea HP Loop Thermowells and rest of thermowells are checked whenever their equipment is opened)
2. Check Valves to be dismentled once in 4 years. You can prioritzed the high pressure Check valves of 1500 rating and above every TA and rest the frequency can be of 4 years. Checks mainly include flapper / disk and their pin (DPT).

I hope this would help. Regards.

[arcpro]

At our site, we have divided the whole piping components to come either under onstream inspections or T/A inspections.
Onstream are obviously those ones which would not be hitting the plant productionand can be inspected on a set frequency.
T/A inspections include those items which cannot be isolated / taken out of service and to be analyzed through a proper study. This study should include the past histories, criticality of service, corrosion /erosion problems etc.

For those operating in corrosive services or with problematic history, we have set their inspection plan for every turnaround.
For those operating under hazardous services, the frequency has been set as 04 years.
All others are inspected after 06 years.
Sometimes, check valves are also inspected during T/A on Operations personnels' call.

[Nabeel Ahmed Qureshi]

thanx all for giving such a detailed response.
arcpro pls let me know the basis of setting freq as 4 & 6 yrs.

[arcpro]

As I have mentioned the piping components having hazardous services which are not corrosive or causing any type of damage like SCC, hydrogen embrittlement, brittle fracture are inspected after 04 years (every second T/A)
Remaining components with low /mild temperature and pressure,non-hazardous / non-toxic services are inspected after 06 years (every third T/A)

These frequencies have been set after several work out sessions with guys from all disciplines.
Hope this clarifies.

[qaisarabbas]

Exxon's International Practices also list down a inspection scope criteria for CVs:
> All CVs having spring loaded mechanism.
> All CVs having siz of 4 inch & above.

Some fertilizer plants inspect these items purely on Operation's Call both at Onstream & Turnaround situations.

[mechcolor]

Inspection frequencies of one plant / facility cannot be directly implemented to other as it is.
It is imperative that the concerned inspection personnel along with process and plant operators must have a complete study before deciding a set inspection frequency. This study must be done system wise in the light of API 574, API 570, API 580 and API 582.

[Nabeel Ahmed Qureshi]

Thanx all for your valuable inputs. It would surely help us to decide the way forward at our site.
Regards
NAq